Sunday, August 31, 2008
Model LE Velocette Twin ...An article reproduced from “Motorcyle Engines”,First series, by staff of The Motor Cycle
0 comments Posted by car 2011 at 3:37 AMGEORGE WILSON Probes into the “Reasons Why” of the lightweight Velocette Design-the 149c.c. Model, Forerunner 
of the Similar 192c.c. Mount-and CHARLES UDALL, Development Engineer, Provides the Answers..
“The component parts of the LE engine are all straightforward. It is the fact that they have been ‘gathered together’-shall we say?-in the way that they have that makes the machine appear unorthodox. It is true to say that in the complete machine not a single departure has been made from what is regarded today as normal engineering principles; obviously to depart from these would have spelt trouble-in large capital letters!”
The photo at the top shows Anne Frampton, daughter of Bertie Goodman last managing director of Veloce Ltd ( himself son of Percy Goodman, the brilliant designer of so many early Velocette engines and inovations) astride Peter Wolfenden's Mk.2 LE at the NSW section of the Australian Velocette Owners Club Show Day at "Fagan Park", on the Northern outskirts of Sydney, 31st August 2008.
Anne is the Club Patron and lives in Sydney.
Thus spoke Mr. Charles Udall, Velocette development Engineer, when I called at the works to discuss the whys and wherefores behind the ingenious design of the 150 c.c. LE Velocette- the most revolutionary lightweight of the day.
“In discussing the LE unit,” he continued, “ I’m afraid that it may be necessary to depart from the strict confines of your ‘Modern Engines’ series. You see, the LE is a conceived-as-a-whole design. The engine, gear box, propeller-shaft, and bevel box all form an integral unit; an entity; a single unit designed to do a specific job. And it is impossible to discuss on ‘section’ of the unit without bringing in a sister section.”
From this stimulating gambit we passed on to a discussion that carried us non-stop through an absorbingly interesting afternoon.
My first question was a multiple one: “Why did you decide on a flat-twin and why, indeed, on a twin at all? Did you ever consider employing a single- a two stroke for instance?”
“Well, first of all,” replied Mr. Udall, “one of the primary aims was elimination, in so far as was possible, of all forms of vibration. There are only three types of engine which could be considered, and of those the flat-twin is really suitable for use in a small-capacity motor cycle. The four-cylinder engine also, of course, eliminates vibration, but obviously the LE is not the sort of machine which could be fitted with a “four.” Whit single, the whole machine would have had to have been made heavier to withstand the inherent vibration, and the steel frame as it exists in the LE today would have proved quite useless. So the question of using a single was never considered, nor was the question of making the engine a two-stroke.
“Again,” Mr. Udall continued, “we come to my other point about one thing leading to another. Since one of the chief aims as I have said, was the elimination of vibration, a flat-twin was decided upon. Since the unit had to be as simple as possible, and lage mileages with a minimum of attention were an important proviso, side-by-side valves were preferred. An objection to overhead-valves was that even a small-capacity engine, the width would considerably be increased, making the engine much more vulnerable. The cylinder heads, in fact, would probably have protected beyond the legshields.
“Linked with the question of ease of maintenance was the decision to use shaft-drive. True, shaft-drive is more expensive than chain. But having a shaft greatly simplifies maintenance for the non-mechanically minded rider, who may be using the machine every day. And the chief aim, after all, was to provide for low maintenance cost as opposed to the lowest production cost.
“The decision to employ shaft-drive arrived at mounting the engine transversely in the frame was a sine qua non. Cooling? Water-cooling was the obvious answer for two reasons; the first was that it is possible to obtain a much higher degree of mechanical quietness when the cylinders are shrouded by water jackets. Taking the conception of the machine as a whole again, legshields must be regarded in the light of essentials, and if air-cooling had been employed, gaps in the shields for the air stream would have been necessary. And that, of course, would have affected weather protection. Another point was that the engine temperature of a small side-valve unit is more easily controlled by means of water-cooling.”
Going into his last point in greater detail, Mr. Udall pointed out that had air-cooling been employed, it would have been next to impossible to incorporate air passages round the exhaust ports.
“The manufacture of engine, clutch, gear box, and final drive as a single unit promised simplification in assembly and manufacturing problems which could not be ignored. Hence the unit construction.”
In one fell swoop, as it were, Mr. Udall had answered about a dozen of the points listed on the rough questionnaire I had prepared. I decided I had better scrap it right away, and deal with each field of inquiry as it cropped up!
Leaving generalities, Mr. Udall went on to point out that the crankshaft is of the two-throw type with the cranks at 180 deg. Since the aim was to keep the offset on the cylinders as low as possible in order to reduce the out-of-balance couple to a minimum, it was desirable to keep down the width of the big-ends. Thus roller-bearings were used. Had plain bearings been adopted, the cylinders would have required to be considerably more offset than they are now, since, in order to achieve the desired load-carrying capacity, considerably wider bearings would have been needed.
The rollers in the big-end bearings are uncaged. There are 28 rollers per bearing. The size of the big-end track on the crankpin is 1in dia. When talking of the big-end track, Udall was referring not to the crankpin itself, but to the hardened sleeve which is pressed on the crankpin.
The obvious question to all of this was: “But why use these sleeves at all- why not a plain, hardened pin of larger sections and grind the bearing surface?”
“Ah!” said Charles, “ that requires some explanation. As you can see. The crankpins and crank discs are a one-piece forging. The metal used is a 3 ½ per cent nickel steel, in fact, B.E.S.69. This is a steel with a high tensile strength and one that is quite ductile. In order to minimize the risk of fracture, and avoid cracks in the angles formed by the pin and disc, these corners have to be radiused. And, of course, since a roller bearing cannot bear on a surface with radiused ends, the big-end tracks, or sleeves, have their inner ends likewise radiused to allow them to be pressed up close to the cheek of the crank disc. An incidental point is that even if it were possible to have the bearings running direct on the crankpin, it would not be possible to use B.E.S.69, since the material cannot be hardened to the necessary degree.”
“I see, and what is the material used for the tracks?”
“It is carbon-chrome steel, turned from bar material, heat-treated and then ground. Incidentally, the sleeves are approximately 1/8in thick.”
I drew Mr. Udall’s attention to the crankshaft bob-weights and what asked: “Why are bob-weights fitted since, surely, with this type of engine, the primary out-of-balance forces are nil?”
“A good point,” answered Charles with a smile. “I grant you that, as the piston and connecting rods in a flat-twin move at the same speed in opposite directions, their inertia forces cancel each other out. But owing to the fact that the cylinders are offset in relation to one another, there exists a slight out-of-balance couple. And this can be reduced by adding bob-weights to the crankshaft. The effect is to reduce the couple in the horizontal plane and introduce a rather higher couple in the vertical plane; but since a motor cycle is very much stiffer in the vertical plane, its effect is nothing like so marked. In other words, it is much to have the couple in the vertical plane than in horizontal.”
“And how are the bob-weights fitted to the crankpins?” I asked.
“The pins are a push fit into the bob-weights. They are locked up by a clamp bolt and lock nut. Then the pins and bob-weight are drilled in position and round, hardened dowels pressed in.”
“With this layout the attractions of adopting the car practice of a combined flywheel and clutch at the rear of the engine seem too good to miss, yet you have ignored them. Any special reason for doing so?” I asked.
“The present arrangement with the flywheel at the front is much better, since, with the existing layout, there is a primary reduction gear between the mainshaft and the clutch. With the clutch running at roughly one-third engine speed, we have a slow-running gear box. This reduces the inertia of the clutch and other rotating parts and makes the great gear-change easier.”
“Fair enough. Is there anything extra ordinary about the main bearings?”
“No, they are perfectly standard ball bearings at both ends with a plain, steady bearing on the driving shaft. It was decided to use ball bearings so that there would be the minimum resistance to starting. The diameter of the ball journal is 3/4in.”
“what material is used for the pistons?”
“They are Y-alloy die-castings; rather unusual in so far as they use a one-piece core in the die. Normally a piston is constructed as a die-casting with anything up to nine separate pieces in the core. Because of the shape of the bosses, the core has to be collapsed when the piston is cast. The LE pistons are made in such a way that the bosses as ‘Dee’d’ up the piston crown.”
I noted that the gudgeon-pin bosses were situated roughly half-way down the piston skirt. “Why is that?” I asked.
Charles replied : “In order to get a proper distribution of load on the piston skirt. If the gudgeon pin is carried high up in the skirt immediately below the slotted oil-control ring, there is intense pressure just at that point and it can lead to seizure. Redistribution of the load makes it possible to use smaller clearances. We use 1 ½ thou. at the skirt.”
“Is the camshaft a forging?”
“Yes, it carries four integral cams. The material is ordinary, case-hardening mild-steel and the cams are casse hardened. The shaft is carried on a ball journal at each end. Diameter of the bearings is 5/16in bore.”
I picked up on of the tiny 10-mm sparking plugs and inquired : “Why use light-alloy heads when the engine is water-cooled?”
“It is generally agreed that light-alloy heads give improved cooling. One can use a slightly higher compression ratio than with an iron head and, of course, there is an advantage of the weight saving.”
I remarked on the fact that the valves were inclined to the bores. Was that as a result of using only a single camshaft or was it also, perhaps, done purposely, in order to get more water round the valve seats?
“Yes, those are the answers. The valve seats are machined in the cylinder casting. Valve-guide material? Plain cast-iron, pressed in. The material used for the valves is normal Silchrome valve steel. Inlet and exhaust valves are made from the same material and the sizes are 13/16in. The compression ratio 6 to 1 Valve springs are of ordinary helical type of 35lb seated strength. Cotters are of the straightforward split type of orthodox design.
“Long tappets of square section with radiused ends are used, and tappet bushes are of sintered cast-iron pressed into the crankcase. Why square-section tappets? Because we wanted to use the widest tappets and cams possible in order to reduce wear to a minimum.”
In answer to a question on how lubrication was carried out, Mr. Udall explained the system thoroughly. “A great-type pump draws oil from the 1 ½-pint capacity sump through a large-capacity gauze filter and delivers to a jet feeding oil to the middle web of the crankshaft. Two scallops formed in the outer diameter of the web direct the oil in to the big-ends. A further feed from the pump leads to the plain, steady bearing on the end of the crankshaft, and to two subsidiary jets: one of these feeds to the camshaft gears, while the other lubricates the reduction drive. Further lubrication is by means of splash and mist.”
We turned to the rear of the engine and I pointed to the primary reduction gear. “Why do you use helical gearing here when a straight-tooth gear would probably do the job just as efficiently?” I asked.
“The answer to that one, of course, is that helical gears are much quieter. An interesting point about the production of the gears is that each pair is lapped on a special machine. This ensures the high degree of accuracy which is essential to really quiet running. It is a procedure used quite a lot in the car world.”
“What material is used for the gears?”
“it is used a 3 percent nickel-chrome-molybdenum steel of 70-80 tons tensile strength.”
“Is it used because of its toughness?”
“The answer to that is ‘yes’-partly; but the real reason it is used is to give a high-core strength the teeth.”
“With this method of unit construction,” I asked, “do you have any troubles owing to the heat transference to the clutch?”
Charles answered that he had experienced none at all. The friction plates themselves are of a high-fade-point material- one which, in other words, can withstand very much higher than normal temperatures before it loses its frictional properties.
“What is the material?” “It is a Ferodo material known as V.M.41.”
“I note that you have interposed the starting mechanism between the clutch and the engine. Why?” “The real reason for that, of course, is to make control easy in difficult circumstances. For instance, if, with the normal starter, the engine stalled during a get-away, it would mean selecting neutral, starting the engine, then re-engaging the gear before getting under way. In this case, all that is necessary is to lift the clutch lever, start the engine and set off.”
“How is the reduction helical fitted to the mainshaft? Is it keyed or fitted on a taper?” I asked.
“It is actually pressed on the present shaft, but it used to be held by splines. It is now pressed on to a very much larger shaft.”
“What is the interference?” “1-1 ½ thou.” “How is it pressed on? “There is a very slight taper in the bore of the gear and on the shaft0, which means that the two can be pushed together so far, and then the operation is completed in a press.”
Pointing to the clutch, Mr. Udall continued, “The clutch, on the other hand, is fitted on splines on the end of the reduction gear shaft and the shaft is carried in one ball journal and one plain bearing.”
“You use a two-plate clutch,” I cut in. “Is there any special reason for that?”
“Well, yes,” he replied. “A single plate clutch of this dimension would have required a much heavier spring pressure to transmit the power. This, of course, would have meant very much heavier clutch operation as light as was humanly possible. We found that with the two plate clutch we had ability to transmit all the power we wanted with the desired lightness of operation.”
“what are the outstanding features of the gear box?”
“Well, it is a constant-mesh, offset box of normal type, but not, of course, a normal gear box as we know it in the motor cycle world. It is one in which the drive is taken in on one shaft and the output taken from the other; in other words, it is not a straight through box, and the drive is always transmitted by one pair of gears only in any gear.”
“Yes, I see that,” I replied, “but is there any reason for using an offset box apart from that of achieving the necessary offset required for the shaft-drive?”
“Yes,” Mr. Udall pointed out, “ there is the additional advantage of low frictional losses since, in the indirect ratios, the power is being transmitted, as I have said, through only one pair of gears- as opposed t two pairs in the normal type of box.”
“What material do you use for the gear pinions?” I asked.
“It is nickel-chrome steel, exactly as used for the reduction helicals, and it is used for the same reasons.”
“What are the shafts made of?” “It is a nickel-chrome case-hardeining steel, known as E.M.39.” “Any special points about its heat-treatment?” “None whatever. It is a perfectly normal case-hardening steel, chosen for its high tensile strength.”
Asking what material was used for the propeller shaft, I was told that it was nickel-chrome oil-hardened steel, also employed because of its high tensile strength-which is about 65 tons per sq in. the shaft operates between a Hardy-Spicer, needle-roller universal joint at the front end, and a splined muff-coupling at the rear.
“What size of bearing is used for the bevel pinion?”
“It is a 3/4in duplex type; a special thrust bearing carrying thrust in both directions. Normal spiral bevels are employed.’
“How is the bearing locked?” “Quite simply,” I was told. “it is shrunk into the housing and locked in position by a screwed ring. The bevel pinion is also carried by a needle roller bearing situated as close up to the teeth as it will go.”
“Any special points about the spiral bevel crown wheel?”
“not really. It is a perfectly normal type, carried by one needle roller bearing and one ball bearing. There is provisions for adjustment in the mesh, which is carried out at the factory. What might be described as an unusual feature is that, since it has a fairly high ratio, it is possible to use a very small bevel box. Drive to the rear wheel is transmitted by a series of dogs.”
All that remained to discuss was the ignition and carburettor.
Dealing with the ignition set first, it will be recalled that a B.T.-H generator is employed. Situated immediately forward of the forged-steel, dished portion, the generator unit is driven on a forward parallel extension of the tapered shaft by a Woodruff key. The casing is held by four bolts extending form the flywheel housing and easily accessible from the front of the engine. In the casing are contained the D.C. generator, h.t. coil, distributor, contact-breaker and auto-timing device, all concealed, all accessible in single compartment.
The carburettor? It had to be one that would provide the perfect tickover. The engine must spring to life at the lightest pull on its starting handle, and it must respond to the most ham-fisted opening up. The result is the special fixed-jet carburettor. It contains only one moving part-a butterfly throttle, and its features a separate starter jet system with in-built push-pull operation. This furnishes the correct mixture for starting and dispenses with the need for a tickler.
Thus spoke Mr. Charles Udall, Velocette development Engineer, when I called at the works to discuss the whys and wherefores behind the ingenious design of the 150 c.c. LE Velocette- the most revolutionary lightweight of the day.
“In discussing the LE unit,” he continued, “ I’m afraid that it may be necessary to depart from the strict confines of your ‘Modern Engines’ series. You see, the LE is a conceived-as-a-whole design. The engine, gear box, propeller-shaft, and bevel box all form an integral unit; an entity; a single unit designed to do a specific job. And it is impossible to discuss on ‘section’ of the unit without bringing in a sister section.”
From this stimulating gambit we passed on to a discussion that carried us non-stop through an absorbingly interesting afternoon.My first question was a multiple one: “Why did you decide on a flat-twin and why, indeed, on a twin at all? Did you ever consider employing a single- a two stroke for instance?”
“Well, first of all,” replied Mr. Udall, “one of the primary aims was elimination, in so far as was possible, of all forms of vibration. There are only three types of engine which could be considered, and of those the flat-twin is really suitable for use in a small-capacity motor cycle. The four-cylinder engine also, of course, eliminates vibration, but obviously the LE is not the sort of machine which could be fitted with a “four.” Whit single, the whole machine would have had to have been made heavier to withstand the inherent vibration, and the steel frame as it exists in the LE today would have proved quite useless. So the question of using a single was never considered, nor was the question of making the engine a two-stroke.
“Again,” Mr. Udall continued, “we come to my other point about one thing leading to another. Since one of the chief aims as I have said, was the elimination of vibration, a flat-twin was decided upon. Since the unit had to be as simple as possible, and lage mileages with a minimum of attention were an important proviso, side-by-side valves were preferred. An objection to overhead-valves was that even a small-capacity engine, the width would considerably be increased, making the engine much more vulnerable. The cylinder heads, in fact, would probably have protected beyond the legshields.“Linked with the question of ease of maintenance was the decision to use shaft-drive. True, shaft-drive is more expensive than chain. But having a shaft greatly simplifies maintenance for the non-mechanically minded rider, who may be using the machine every day. And the chief aim, after all, was to provide for low maintenance cost as opposed to the lowest production cost.
“The decision to employ shaft-drive arrived at mounting the engine transversely in the frame was a sine qua non. Cooling? Water-cooling was the obvious answer for two reasons; the first was that it is possible to obtain a much higher degree of mechanical quietness when the cylinders are shrouded by water jackets. Taking the conception of the machine as a whole again, legshields must be regarded in the light of essentials, and if air-cooling had been employed, gaps in the shields for the air stream would have been necessary. And that, of course, would have affected weather protection. Another point was that the engine temperature of a small side-valve unit is more easily controlled by means of water-cooling.”
Going into his last point in greater detail, Mr. Udall pointed out that had air-cooling been employed, it would have been next to impossible to incorporate air passages round the exhaust ports.
“The manufacture of engine, clutch, gear box, and final drive as a single unit promised simplification in assembly and manufacturing problems which could not be ignored. Hence the unit construction.”
In one fell swoop, as it were, Mr. Udall had answered about a dozen of the points listed on the rough questionnaire I had prepared. I decided I had better scrap it right away, and deal with each field of inquiry as it cropped up!Leaving generalities, Mr. Udall went on to point out that the crankshaft is of the two-throw type with the cranks at 180 deg. Since the aim was to keep the offset on the cylinders as low as possible in order to reduce the out-of-balance couple to a minimum, it was desirable to keep down the width of the big-ends. Thus roller-bearings were used. Had plain bearings been adopted, the cylinders would have required to be considerably more offset than they are now, since, in order to achieve the desired load-carrying capacity, considerably wider bearings would have been needed.
The rollers in the big-end bearings are uncaged. There are 28 rollers per bearing. The size of the big-end track on the crankpin is 1in dia. When talking of the big-end track, Udall was referring not to the crankpin itself, but to the hardened sleeve which is pressed on the crankpin.
The obvious question to all of this was: “But why use these sleeves at all- why not a plain, hardened pin of larger sections and grind the bearing surface?”
“Ah!” said Charles, “ that requires some explanation. As you can see. The crankpins and crank discs are a one-piece forging. The metal used is a 3 ½ per cent nickel steel, in fact, B.E.S.69. This is a steel with a high tensile strength and one that is quite ductile. In order to minimize the risk of fracture, and avoid cracks in the angles formed by the pin and disc, these corners have to be radiused. And, of course, since a roller bearing cannot bear on a surface with radiused ends, the big-end tracks, or sleeves, have their inner ends likewise radiused to allow them to be pressed up close to the cheek of the crank disc. An incidental point is that even if it were possible to have the bearings running direct on the crankpin, it would not be possible to use B.E.S.69, since the material cannot be hardened to the necessary degree.”
“I see, and what is the material used for the tracks?”
“It is carbon-chrome steel, turned from bar material, heat-treated and then ground. Incidentally, the sleeves are approximately 1/8in thick.”
I drew Mr. Udall’s attention to the crankshaft bob-weights and what asked: “Why are bob-weights fitted since, surely, with this type of engine, the primary out-of-balance forces are nil?”
“A good point,” answered Charles with a smile. “I grant you that, as the piston and connecting rods in a flat-twin move at the same speed in opposite directions, their inertia forces cancel each other out. But owing to the fact that the cylinders are offset in relation to one another, there exists a slight out-of-balance couple. And this can be reduced by adding bob-weights to the crankshaft. The effect is to reduce the couple in the horizontal plane and introduce a rather higher couple in the vertical plane; but since a motor cycle is very much stiffer in the vertical plane, its effect is nothing like so marked. In other words, it is much to have the couple in the vertical plane than in horizontal.”
“And how are the bob-weights fitted to the crankpins?” I asked.
“The pins are a push fit into the bob-weights. They are locked up by a clamp bolt and lock nut. Then the pins and bob-weight are drilled in position and round, hardened dowels pressed in.”
“With this layout the attractions of adopting the car practice of a combined flywheel and clutch at the rear of the engine seem too good to miss, yet you have ignored them. Any special reason for doing so?” I asked.
“The present arrangement with the flywheel at the front is much better, since, with the existing layout, there is a primary reduction gear between the mainshaft and the clutch. With the clutch running at roughly one-third engine speed, we have a slow-running gear box. This reduces the inertia of the clutch and other rotating parts and makes the great gear-change easier.”
“Fair enough. Is there anything extra ordinary about the main bearings?”
“No, they are perfectly standard ball bearings at both ends with a plain, steady bearing on the driving shaft. It was decided to use ball bearings so that there would be the minimum resistance to starting. The diameter of the ball journal is 3/4in.”
“what material is used for the pistons?”
“They are Y-alloy die-castings; rather unusual in so far as they use a one-piece core in the die. Normally a piston is constructed as a die-casting with anything up to nine separate pieces in the core. Because of the shape of the bosses, the core has to be collapsed when the piston is cast. The LE pistons are made in such a way that the bosses as ‘Dee’d’ up the piston crown.”
I noted that the gudgeon-pin bosses were situated roughly half-way down the piston skirt. “Why is that?” I asked.
Charles replied : “In order to get a proper distribution of load on the piston skirt. If the gudgeon pin is carried high up in the skirt immediately below the slotted oil-control ring, there is intense pressure just at that point and it can lead to seizure. Redistribution of the load makes it possible to use smaller clearances. We use 1 ½ thou. at the skirt.”“Is the camshaft a forging?”
“Yes, it carries four integral cams. The material is ordinary, case-hardening mild-steel and the cams are casse hardened. The shaft is carried on a ball journal at each end. Diameter of the bearings is 5/16in bore.”
I picked up on of the tiny 10-mm sparking plugs and inquired : “Why use light-alloy heads when the engine is water-cooled?”
“It is generally agreed that light-alloy heads give improved cooling. One can use a slightly higher compression ratio than with an iron head and, of course, there is an advantage of the weight saving.”
I remarked on the fact that the valves were inclined to the bores. Was that as a result of using only a single camshaft or was it also, perhaps, done purposely, in order to get more water round the valve seats?
“Yes, those are the answers. The valve seats are machined in the cylinder casting. Valve-guide material? Plain cast-iron, pressed in. The material used for the valves is normal Silchrome valve steel. Inlet and exhaust valves are made from the same material and the sizes are 13/16in. The compression ratio 6 to 1 Valve springs are of ordinary helical type of 35lb seated strength. Cotters are of the straightforward split type of orthodox design.
“Long tappets of square section with radiused ends are used, and tappet bushes are of sintered cast-iron pressed into the crankcase. Why square-section tappets? Because we wanted to use the widest tappets and cams possible in order to reduce wear to a minimum.”
In answer to a question on how lubrication was carried out, Mr. Udall explained the system thoroughly. “A great-type pump draws oil from the 1 ½-pint capacity sump through a large-capacity gauze filter and delivers to a jet feeding oil to the middle web of the crankshaft. Two scallops formed in the outer diameter of the web direct the oil in to the big-ends. A further feed from the pump leads to the plain, steady bearing on the end of the crankshaft, and to two subsidiary jets: one of these feeds to the camshaft gears, while the other lubricates the reduction drive. Further lubrication is by means of splash and mist.”
We turned to the rear of the engine and I pointed to the primary reduction gear. “Why do you use helical gearing here when a straight-tooth gear would probably do the job just as efficiently?” I asked.
“The answer to that one, of course, is that helical gears are much quieter. An interesting point about the production of the gears is that each pair is lapped on a special machine. This ensures the high degree of accuracy which is essential to really quiet running. It is a procedure used quite a lot in the car world.”
“What material is used for the gears?”
“it is used a 3 percent nickel-chrome-molybdenum steel of 70-80 tons tensile strength.”
“Is it used because of its toughness?”
“The answer to that is ‘yes’-partly; but the real reason it is used is to give a high-core strength the teeth.”
“With this method of unit construction,” I asked, “do you have any troubles owing to the heat transference to the clutch?”
Charles answered that he had experienced none at all. The friction plates themselves are of a high-fade-point material- one which, in other words, can withstand very much higher than normal temperatures before it loses its frictional properties.
“What is the material?” “It is a Ferodo material known as V.M.41.”
“I note that you have interposed the starting mechanism between the clutch and the engine. Why?” “The real reason for that, of course, is to make control easy in difficult circumstances. For instance, if, with the normal starter, the engine stalled during a get-away, it would mean selecting neutral, starting the engine, then re-engaging the gear before getting under way. In this case, all that is necessary is to lift the clutch lever, start the engine and set off.”
“How is the reduction helical fitted to the mainshaft? Is it keyed or fitted on a taper?” I asked.
“It is actually pressed on the present shaft, but it used to be held by splines. It is now pressed on to a very much larger shaft.”
“What is the interference?” “1-1 ½ thou.” “How is it pressed on? “There is a very slight taper in the bore of the gear and on the shaft0, which means that the two can be pushed together so far, and then the operation is completed in a press.”
Pointing to the clutch, Mr. Udall continued, “The clutch, on the other hand, is fitted on splines on the end of the reduction gear shaft and the shaft is carried in one ball journal and one plain bearing.”
“You use a two-plate clutch,” I cut in. “Is there any special reason for that?”
“Well, yes,” he replied. “A single plate clutch of this dimension would have required a much heavier spring pressure to transmit the power. This, of course, would have meant very much heavier clutch operation as light as was humanly possible. We found that with the two plate clutch we had ability to transmit all the power we wanted with the desired lightness of operation.”
“what are the outstanding features of the gear box?”
“Well, it is a constant-mesh, offset box of normal type, but not, of course, a normal gear box as we know it in the motor cycle world. It is one in which the drive is taken in on one shaft and the output taken from the other; in other words, it is not a straight through box, and the drive is always transmitted by one pair of gears only in any gear.”
“Yes, I see that,” I replied, “but is there any reason for using an offset box apart from that of achieving the necessary offset required for the shaft-drive?”
“Yes,” Mr. Udall pointed out, “ there is the additional advantage of low frictional losses since, in the indirect ratios, the power is being transmitted, as I have said, through only one pair of gears- as opposed t two pairs in the normal type of box.”
“What material do you use for the gear pinions?” I asked.
“It is nickel-chrome steel, exactly as used for the reduction helicals, and it is used for the same reasons.”
“What are the shafts made of?” “It is a nickel-chrome case-hardeining steel, known as E.M.39.” “Any special points about its heat-treatment?” “None whatever. It is a perfectly normal case-hardening steel, chosen for its high tensile strength.”
Asking what material was used for the propeller shaft, I was told that it was nickel-chrome oil-hardened steel, also employed because of its high tensile strength-which is about 65 tons per sq in. the shaft operates between a Hardy-Spicer, needle-roller universal joint at the front end, and a splined muff-coupling at the rear.
“What size of bearing is used for the bevel pinion?”
“It is a 3/4in duplex type; a special thrust bearing carrying thrust in both directions. Normal spiral bevels are employed.’
“How is the bearing locked?” “Quite simply,” I was told. “it is shrunk into the housing and locked in position by a screwed ring. The bevel pinion is also carried by a needle roller bearing situated as close up to the teeth as it will go.”
“Any special points about the spiral bevel crown wheel?”
“not really. It is a perfectly normal type, carried by one needle roller bearing and one ball bearing. There is provisions for adjustment in the mesh, which is carried out at the factory. What might be described as an unusual feature is that, since it has a fairly high ratio, it is possible to use a very small bevel box. Drive to the rear wheel is transmitted by a series of dogs.”
All that remained to discuss was the ignition and carburettor.
Dealing with the ignition set first, it will be recalled that a B.T.-H generator is employed. Situated immediately forward of the forged-steel, dished portion, the generator unit is driven on a forward parallel extension of the tapered shaft by a Woodruff key. The casing is held by four bolts extending form the flywheel housing and easily accessible from the front of the engine. In the casing are contained the D.C. generator, h.t. coil, distributor, contact-breaker and auto-timing device, all concealed, all accessible in single compartment.
The carburettor? It had to be one that would provide the perfect tickover. The engine must spring to life at the lightest pull on its starting handle, and it must respond to the most ham-fisted opening up. The result is the special fixed-jet carburettor. It contains only one moving part-a butterfly throttle, and its features a separate starter jet system with in-built push-pull operation. This furnishes the correct mixture for starting and dispenses with the need for a tickler.
Acknowledgement is made to Mortons Motorcycle Media owners of the copyright for "The Motorcycle" and "Motor Cycling" material.
Left click on images to enlarge...
Wednesday, August 27, 2008
I've been a regular visitor to the annual NZ Historic Racing Register race classic race meeting at the Pukekohe circuit, south of Auckland, NZ.
In fact Hugh Anderson ( four times world champion in the "tiddler" classes on the European GP circuits) visited the annual Easter race meeting at Bathurst, NSW in possibly 1978 to view the historic machine race and speak with some of us over the plans to run a similar event in NZ.
The inaugeral meeting took place in early Feb.1980 and three Aussies were invited to attend, Elmer McCable on a 7R AJS, Eric Debenham on a 1000cc Norton Vincent special and myself on a 1939 Mk.8 KTT Velocette.
We had a great time.
I took Velocettes over for the next few years, borrowed bikes for a few more years then went over regularly to spectate from then on.
The NZ HRR were very astute with the promotion and after accumulating some funds from successful meetings, started inviting overseas riders with famous racing motorcycles to be guests at the meeting.
Ivan Rhodes and the 1939 Velocette Roarer, Sammy Miller on the 1939 supercharged AJS 4, John Surtees on several occasions with a Vincent "Grey Flash", the 1939 supercharged BMW, Paul Smart on the 75o Imola Ducati, the ex Hailwood 500cc Honda-4 racer...the list goes on.
This blog features some photos from the 2003 event, where the special guest machine was a Moto Guzzi V8 500cc racer.
There are always very inovative ideas in NZ..and Pukekohe is the place to see many of them.
In these photos you will see new Manx Norton engines with desmo valve operation, special Venom Velo racers etc...as well the special Velocette trophy, donated by Veloce Ltd in the 1930s to White's the Auckland based Velo importers, left idle for many years and now resurfaced to be presented annually at the meeting.
Left click on the photos to enlarge.
Saturday, August 23, 2008
Time for another foray into pen and ink drawings from the motorcycle media, 
graphic art has changed dramatically …. lets have another look into 1931 and 1933 when graphic artists, cartoonists and the like, armed with pen, ink and pencil recorded the images of the day in concert with the film camera.
Acknowledgement is made to Mortons Motorcycle Media owners of the copyright for "The Motorcycle" and "MotorCycling" and to the families of the artists for use of the images.
Left click on images to enlarge..
Thursday, August 21, 2008
The Motorcycle trade in the UK held motorcycle shows
annually, with the exception of the war years from the 1920s into the late 1970s, initially at the Olympia venue in London, then from the latter 1930s at the Earls Court venue also in London.
annually, with the exception of the war years from the 1920s into the late 1970s, initially at the Olympia venue in London, then from the latter 1930s at the Earls Court venue also in London.Usually held in November, it showcased the next years models.
This blog features the 1938 Earls Court show catalogue, featuring the 1939 ranges of motorcycle, bicycles and associated accessories ...listed for 6d and ½" thick for the show held over the period 7th to 12th November and I've scanned in some of the contents for a look back then...
This blog features the 1938 Earls Court show catalogue, featuring the 1939 ranges of motorcycle, bicycles and associated accessories ...listed for 6d and ½" thick for the show held over the period 7th to 12th November and I've scanned in some of the contents for a look back then...
Left click to enlarge the illustrations.
Wednesday, August 20, 2008
Velocette data from a variety of sources....Velocette Lucas automatic advance unit information...
0 comments Posted by car 2011 at 5:18 AMWhen Veloce Ltd introduced the "alloy" MAC in a spring frame in 1953, they fitted Lucas K1F magnetos to their engines and continued with this until Lucas ceased supply of magnetos in the late 1960s...the exception being the scrambler and some Clubman Venom and Viper Clubmans models ( 1958-62) which had manual advance TT BTH magnetos..likely some old stock held by Veloce.
They also utilised the new Lucas automatic advance unit on these magnetos.
Prior to this, in 1937, in collaboration with BTH, the first automatic advance inits were introduced to the MOV,MAC and MSS range.
Illustrated is one from the Bob Burgess "Red book" on Velocette.
Most Velocette riders assume there is only one Lucas automatic advance unit type used on the engines mentioned above, however there are three... for years I also was ignorant of this fact.
But between 1952-54 on the "alloy" MAC and the newly introduced "alloy" MSS, Lucas automatic advance unit 47522A was fitted...it had an advance range of 16½ ° to 18½ °, which is 33° to 37° at the crankshaft.
This meant that if you timed the ignition at the recommended full advance, in the case of the MAC, 38° BTDC, you had only 1° to 5°BTDC at full retard when you were starting the motorcycle. Worse still the MSS had 36° full advance BTDC so if you were lucky you had 3° of advance BTDC fully retarded or even 0° or less.
Velocette's have a low kickstarter ratio, so when kicking, the engine often didn't easily start. When pushed, and so with a faster engine speed and the auto advance unit starting to advance you had more ignition advance, the bike would start.
Many a carburettor was blamed for the poor starting.
In 1955, Lucas introduced the 47545A unit with 11° to 13° span or 22° to 26° at the crankshaft.
This meant at full retard you had around 15° plus BTDC advance and starting was easier.
You do need a minimum advance to easily start a Velocette....
Both these units used the same advance springs, and regretably I cannot find any information on their characteristics.
With the Venom and Viper introduction in 1956, Lucas introduced another unit, type 47576A with the same advance range as the replaced unit 47545A, but different advance unit springs.
Again there appears to be no information on this spring characteristics.
All we can surmise is that the advance curve varied between these units.
Problem is all the units look identical.....
You would need to discover a brand new, old stock unit in its box, with the part number on it and then you could have the spring tension measured.
Interesting stuff....
Back to the BTH advance unit, and again I have no information on it, but it appears to suffer from wear and often has up to 50° advance span, so timing it on full advance, means for sure the unit will fire after TDC and the bike will be a pig to start.
A Venom I had, fitted with such a unit caused me so much anguish... I tried three carburettors, including a brand new Amal Monobloc before I looked at the auto advance unit, a BTH and removed it , checked its advance span...it was around 40°, so I had no hope.
A replacement Lucas made a better starter of it, but now I utilise fixed ignition timing, with a bronze gear, 34° advance all the time.
The bike starts OK providing you leave the throttle alone and fully closed, allowing the pilot system only to work.
Finally the details of these units...
The teeth are 92 teeth, 32D.P. ( diametrical pitch), 16° helix angle. ( Veloce used other angles but these were in the early 1930s).
The magneto taper...another piece of information which eluded me for years is.. a 1 in 5 taper.
Left click on images to enlarge for better viewing.
Monday, August 18, 2008
Over the years I've collected lots of Velocette data, some from the usual sources such as Bob Burgess's red book on 
Velocette ( more on this in a later book review blog ), others from proprietary suppliers catalogues, lots of which I photocopied and pasted onto cardboard pages, making up a folder and from there I further photocopied into files to share with others... so I'm going to run a series from them, not in any particular order and this first lot are from the control lever people Doherty, the grease nipple and grease gun people Tecalamit and the tyre pump people Apex Inflaters....
An interesting point about control levers is that the pivot point 
to the centre of the cable nipple was made in several sizes..7/8"(0.875"), 1 and 1/16"(1.0625") etc.
to the centre of the cable nipple was made in several sizes..7/8"(0.875"), 1 and 1/16"(1.0625") etc.Velocette use 7/8" on the front brake lever, but 1 and 1/16" on the clutch.
You can get 7/8" clutch lever centre to centre dimensioned levers and this has caused many a headache for Velocette people whose clutch appears to not fully release....
Left click on the images to enlarge and to access the data.
Sunday, August 17, 2008
499cc MSS...An article reproduced from “Motorcycle Engines”, Second series, by staff of The Motor Cycle
0 comments Posted by car 2011 at 4:39 AMAlan Baker, journalist,questions the “Reasons Why” of the new swinging arm 
Velocette design-the 499c.c. Model MSS, a new all alloy engine-and CHARLES UDALL, Development Engineer, Provides the Answers. ( introduced for the 1954 season by Veloce Ltd.).
For many years Velocette machines have rightly had a special place in the regard of the more technically minded enthusiast. Not only have Velocettes amassed as impressive list of racing successes, but the level of engineering quality and technique applied to production models has always been of an unusually high order. Introduced towards the end of the 1935 season, the original 495 c.c. MSS engine was a logical development from the 348 c.c. MAC model, which in turn was evolved from the 248c.c. MOV- the first push-rod over-head valve unit to be introduced by the concern. The MSS quickly earned itself an enviable reputation as a quiet, docile machine which, although it had excellent manners, lacked nothing in sheer performance in comparison with its contemporaries. 
In the early post-war years, the model was reintroduced in virtually its 1939 form, but was dropped after 1948; such were the manufacturing difficulties at the time that it was decided to concentrate production resources on the LE and MAC models. In 1951, the MAC engine appeared in a considerably redesigned form, with light-alloy cylinder and cylinder head.
As a result of the easing of manufacturing problems during the last two or three years, and the demand from Velocette adherents for a larger-capacity machine, it was decided to work on a new MSS power unit. In the interests of economic production, the MSS engine would be housed in the newly developed MAC rear-sprung frame, and would embody the proven features of its ancestors together with the lessons learned from the MAC.
Although it bore a similarity to the earlier version, the new MSS engine differed considerably there from in its internal details. Possibly the most obvious change concerned the bore and stroke which, from being 81mm x 96mm, became “square” at 86mm x 86mm. The engine had the familiar high-camshaft operation of the overhead valves, and emerged as a functional and efficient-looking unit
Charles Udall, who was responsible for the design, has been with Veloce, Ltd., since 1927 and, in pre-war years, was on the racing side under the late Harold Willis; on Willis’ death in 1939, Mr. Udall took over the racing department and, after the war, became development engineer. In this capacity he is concerned not only with laying out a design on paper but also with ensuring that it comes up to expectations after its translation into metal- an ideal combination to a technician in search of information.
To after the bore and stroke of a successful engine is a major step, not to be undertaken lightly by any designer. Hence my first query:
Question: “Does the 86mm bore and stroke mean that you are now in favour of comparatively short strokes and big bores, or is some other consideration involved?”
Answer: “The reason for the changed dimensions is very simple. We decided to use the current spring frame to house the new MSS engine, and the size of this frame is such that the old “long-stroke” engine was too tall to go in- so we shortened its stroke until it would fit. Where very high rpm. are necessary, as on a racing engine, a short stroke is essential, but the average roadster engine is in a different category and there is, in my opinion, no intrinsic advantage, in a bore/stroke ratio approaching or exceeding unity. A very tall engine will tend to be heavier than a short one and, if the stroke is over-long, difficulty will be encountered in getting adequate sizes of valves. With in certain limits, however, I consider that I could get almost identical characteristics and performance from any bore/stroke ratio.”
I had expected a technical lecture and had received a straightforward admission of expediency! We then considered the crankshaft assembly, and Mr. Udall pointed out that the flywheels, though comparatively narrow, are of large diameter with rims of fairly deep section, thus providing maximum flywheel effect with minimum weight.
Shallow-Taper Fit
Question: “I notice that there are no nuts for securing the mainshaft or the crankpin in the flywheels. Presumably you employ interference fits, but the absence of nuts is unusual in the case of the crankpin, and represents a difference from the earlier MSS engine. Why have you adopted this particular method of construction?”
Answer: “The mating parts have a taper of 0.008" per inch. This taper enables each shaft to be entered in its hole without difficulty during assembly and gives an interference fir of 0.003" to 0.0035" when fully home-ample for complete security. The elimination of the crankpin nuts has meant that we no longer have to counter-bore the flywheels to accommodate the nuts, and thus have almost twice the length of crankpin shank held in each wheel than we had before. In addition, we have increased the diameter of the shank; the combined effect of the two alterations, plus the reduced throw of the crank, is a very much stiffer flywheel assembly. Incidentally, we have employed the shallow-taper method of construction since 1925.”
It is of the utmost importance that the materials used for the various components of the crankshaft assembly should be up to the loading imposed on them. For this reason, the flywheels are stampings in a 0.3%, carbon steel, the crankpin is a 3 %, nickel-chromium, case-hardening steel, and the drive-side and timing-side shaft a direct-hardening steel is employed.
For the connecting rod En18, a 1% chromium steel, is employed and the forging is heat-treated to 60 tons/sq in tensile strength. The heat treatment is carried out before machining, to avoid distortion, and the usual hardened sleeve is pressed in to form the outer race of the big-end bearing.
Question: “On the ‘iron’ engine you balanced 70% of the reciprocating weight, whereas on the new engine only 55% is balanced. Does this alteration result from the reduced weight of the engine?”
Answer: “While the reduced weight might have had an effect, one cannot say that there is an optimum balance factor for an engine on its own: there is only an optimum factor for a giver engine-and-frame combination, which includes the method of mounting the engine in the frame. Here we have an engine of altered dimensions and weight from the earlier model, housed in a completely different frame. It would have been most surprising had the best balance factor proved to be the same for both machines. There is no known method of forecasting the best balance factor for any particular combination so it has to be ascertained by experiment.”
Interesting comment, as the balance factor was changed back to 70% around the introduction of the Venom in 1956. DQ.
High Load Capacity
The MSS engine is probably unique in that it has taper-roller bearings to support the mainshafts, in place of the more usual ball or parallel-roller pattern. These taper-roller bearings were first introduced on the post-war “long-stroke” MSS engine and proved so satisfactory that they were retained in the new design.
Bearings of this type have a high load-carrying capacity for their size, and are less affected than are other varieties by out-of-line forces caused by shaft deflection, which cannot be completely avoided in any engine. Also, the taper-roller bearing is intended to withstand axial as well as radial loading and so is admirably suited to dealing with the end-thrust imposed by the helical timing gears.
With quiet operation in mind, a degree of pre-loading is applied to the main bearings; this “nip”, as it is called, is not in any way harmful to the bearings. It ensures absence of play between rollers and races, so that “grumbling” during running is avoided.
The inner races are pressed on to the mainshafts. The outer races are pressed into the crankcase halves, where they are shimmed to provide a nip of 0.004" when the engine is cold. At normal running temperatures this nip comes down to between ½ and ¾ thou. It is recommended by the makers that after 10 to 15,000 miles, by which time the bearings will have thoroughly bedded down, the crankcase should be dismantled and the outer races re-shimmed to restore the pre-loading to its original figure. Thereafter no further attention should be necessary for the rest of this life of the bearing.
Question: “In this new engine you retain the traditional, narrow crankcase, with only one bearing for each mainshaft. Since so many other manufactures employ two bearings, at least on the drive side, can you tell me the reasons for your layout?”
Second Bearing Unnecessary
Answer: “Many years ago we decided to keep the primary chain line as close as possible to the engine centre line. This necessitated our putting the primary drive inside the final drive. Although this feature resulted in a more complicated clutch-operating mechanism, the absence of overhang and the consequently short, stiff mainshaft enabled us to dispense with a second drive-side main bearing which would undoubtedly be necessary if we had a conventional drive layout. On the timing side, the mainshaft pinion is located right up against the outside of the bearing, so that here, too, the shaft is short and stiff enough to require no out board support.”
Question : “For the big-end bearing you employ a single row of 3/16" x 9/16" rollers in a Duralumin cage, in place of the more common two rows (or even three) of shorter rollers. What benefit do you consider to accrue from the use of these long rollers?”
Answer: “All bearing rollers have radiused- or chamfered-ends, to avoid flaking of the case at these points. These end radii reduce appreciably the effective length of the roller, so that three rows of 3/16" x 3/16" rollers would have a lower bearing capacity than has our single row. You will note that the ends of the cage which runs on the crankpin, are located in shallow recesses in the flywheels, so that the rollers virtually fill the gap between the wheels. This avoidance of wasted width assists in achieving a narrow rigid crankshaft assembly.”
Engine lubrication is by gear-type pump driven by a bronze worm on the end of the timing-side mainshaft; to ensure through scavenging of the crankcase, the scavenge-pump capacity has been increased and is nearly two and a half times that of the pressure side.
On leaving the pump, the oil is forced to a gallery in the timing cover, whence it passes to four separate feeds: one leads to a big-end bearing via the mainshaft, another lubricates the cam-spindle bearing, the third directs oil to the cam faces, and the last takes oil to the rocker gear. Oil is supplied in the desired quantity and at a suitable pressure for each duty by means of jets and metering holes.
Several features requiring comment emerged from a study of the lubrication system, so I put the following questions to Mr. Udall.
Non-return valve
Question: “A disadvantage of the gear-type oil pump is its tendency to let oil seep past it into the crankcase, so that over-oiling can result on starting after the engine has not been running for some time. Have you made any provision to deal with this difficulty?”
Answer : “We encountered the trouble on earlier engines, and have taken two steps to eliminate it on the MSS unit. In non-return ball valve, held on its seat by a light spring when the engine is not running. Pump suction is sufficient to take the ball off its seat so that oil can flow from the tank to engine. Though unusual, this method has proved entirely satisfactory, provided only that the feed pipe is fully primed with oil before it is coupled to the tank. On the scavenge side, the oil is returned through a fabric filter in the tank and, to prevent the oil in the filter from draining back, the return pipe is extended above the top of the filter.”
Improved Lubrication
Question: “Big-end lubrication on the earlier engines was by the usual drill ways in mainshaft, flywheel and crankpin, but I note that the crankpin is no longer drilled. Instead, the drill way in the flywheel is inclined and emerges at the inner face slightly nearer to the centre than the crankpin. What is the advantage of this over the former method?”
Answer: “Where the crankpin is drilled axially, centrifugal force results in the oil tending to go only to the outer part of the bearing, so that the rollers nearer the axis of the flywheel may be under-lubricated. By supplying the oil to the point of the bearing nearest to the centrifuged through the whole of the bearing, so that more through lubrication is obtained.”
Question: “The rocker gear is fed from the pressure side of the oil pump, and not from the scavenge side as on many other engines popular today. Also, the pipe from the timing chest is no less than 5/16in in outside diameter. Why do you not lubricate from the scavenge pump, and why is the pipe so large?”
Answer : “Lubrication from the scavenge pump may result in some restriction in efficiency and hence inadequate scavenging. Also the pressure is so low that, in conjunction with a fair length of small-bore piping, little real lubrication can result, particularly when the oil is cold.
“We prefer to use the pressure pump to make sure the oil gets to where it is wanted, to give it passages of adequate size through which to flow, and to restrict the quantity by the use of metering holes at the component in concerned-in this case the rocker bearings, where the oil emerges through 0.046" holes.
Another feature to be carried on unchanged from the earlier-series engines is the timing gear. All push-rod Velocette engines have had small-pitch, helical-cut teeth in the timing train; despite their rather higher manufacturing cost, such gears are considered to be well worth while since they operate more quietly than do straight-toothed gears. The reason for this quieter running is that more than one tooth is always in full engagement over part if its length; thus, the driving load is not transferred suddenly from one tooth to the next but the changeover is relatively gradual and smooth.
Adjustment of Backlash
A diametral pitch (number of teeth divided by pitch circle diameter) of 32 is employed, and the intermediate idler gear between the crankshaft pinion and the cam wheel has a hunting tooth to distribute wear. This idler also has an adjustable mounting whereby backlash can be taken up-a further point making for quiet running. The fixed spindle on which it revolves has a circular back plate with three tapped holes; there are three similarly spaced holes in the crankcase wall through which pass the set-screws securing the back plate. Adequate clearance is allowed in these second three holes to give the necessary meshing adjustment which is held when the screws are tightened. On erection, the adjustment is set so that all backlash is just taken up with the engine cold.
Spindle Support
As mentioned earlier by Mr. Udall, the mainshaft pinion is carried close up to the main bearing. It follows that the intermediate and cam gears also have little overhang from the crankcase wall; both are bronze bushed, and the cam spindle is pressed into the case. An outboard steady plate supports the outer ends of the two gear spindles and that carrying the cam followers. The steady plate is tied to the crankcase at two points, and thus not only maintains the spindles in correct relation with each other but also with the crankshaft.
The taper-interference fit mentioned in connection with the crankpin and mainshafts is also found between the cam wheel and the sleeve on which the cams are formed. In this case the taper that the parts are self-gauging: if the fit is correct, the sleeve will enter exactly half-way through the wheel when inserted by hand. If it went less far, the interference fit on pressing it home would be too heavy, while entry beyond the halfway point would result in too light an interference.
Question: Compared with that of many other engines, the valve timing of the MSS engine is very ‘moderate’ and provides only 38 degrees of overlap. This reduction from the 60 degrees of earlier MSS engines was presumably made with a view to economy and good torque lower down the speed range. Has any serious loss in top-end performance resulted and, if not, how have you avoided the loss?”
Increased Radius
Answer: “ You are right in your assumption that we were guided primarily by the need for economy and better low speed pulling. However, there is no serious loss at the top, as is indicated by the peak power output of 23b.h.p. at 5,000rpm, with air cleaner and standard silencer. We have obtained this peak performance by an alteration to the bottom rockers (cam followers). These rockers have a radius of 1" instead of 3/8" as with the former engine. This larger radius results in quicker acceleration of the valve off its seat, and a longer deceleration period towards full lift.
“With a fairly high valve lift, the deceleration period must be as long as possible if the valve mechanism is going to follow the cam motion at high rpm. which it must do if float is to be avoided. Softer timing means that the total period available for opening (or closing) the valve is lessened, so that only by speeding up the acceleration stage was it possible to maintain an adequate valve lift with the new timing.”
While the fuel consumption under road conditions must await an independent road test, Charles Udall is confident that the MSS will prove economical. The effect of the modified valve timing on the torque curve has been most marked. Although the actual torque peak occurs as before at about 4,000 rpm the torque is very nearly constant between 3000 and 4,500rpm. after which it falls off rather sharply. Since the torque figure is still good at as low as 2,500 rpm. it should obviously be possible to drive the MSS largely as a top-gear machine if desired, and it should have excellent characteristics for sidecar work.
The cam followers referred to by Mr. Udall are of 3% nickel, case hardening steel and have a hard-facing alloy in the rubbing radius. Push rods are of Duralumin tubing with hardened steel ball-ends pressed into the lower ends.
Checking the Clearance
An unusual arrangement is employed at the rocker adjusters. The rocker carries a threaded, ball-end adjuster which seats in a cup formed in a hardened-steel mushroom. The stem of the mushroom is a sliding fit in the bore of the push rod, and the underside of its head forms a flat shoulder. On to the end of the push rod is pressed a shouldered sleeve; the shoulder of the mushroom seats on the flat top face of this sleeve.
It will be evident that the clearance between shoulder and sleeve face will be a measure of the valve clearance, which is checked by sliding a feeler into the gap. The adjacent corners of sleeve and mushroom have a small radius to assist the insertion of the feeler.
Apart from improved accessibility, this adjustment scheme has an advantage over a threaded adjuster at the valve end of the rocker. The thrust button which bears on the valve can be radiused in one plane only instead of being part-spherical. The resulting line contact causes less wear of the valve stem than did the almost point contact of the part-spherical button employed for the earlier engine.
Holding-down Studs
When redesigning the MAC engine, Y-alloy was adopted for the cylinder head on account of its mechanical strength and its good heat conductivity. The latter feature permits the use of a higher compression ratio than does cast iron, thereby improving both performance and fuel consumption. Since it was clearly desirable that the MSS should not lag behind in these two respects, Y-alloy forms the head material on this engine also.
Shrunk into the head are valve seats of austenitic iron. This material was chosen because of its resistance to impact loading at elevated temperatures, and because of the security it provides through having a coefficient of expansion approaching that of Y-alloy. Four long holding-down studs pass through the head and the upper fins of the Al-fin cylinder barrel, and these studs gave rise to my next point
Question: “The four cylinder and head holding-down studs screw into steel sleeves which in turn screw into the crankcase. Surely such sleeves are unnecessary with semi-permanent items such as the studs?”
Answer: “They would be unnecessary if the studs were semi-permanent, but the height restriction of the frame is such that the studs have to be removed before the head can be lifted. Removal of the head will normally be infrequently required, but we thought it as well to guard against the inveterate “dismantler” by ensuring that no crankcase threads would strip.”
An unusual detail is that the head holding-down nuts have nylon inserts which, in addition to being self-locking, seal the threads against oil leakage from the head and down the studs.
On top of the head is bolted the rocker box, a die-casting in DTD424 aluminium alloy. Two half-bearings are machined in the box to take the journal portion of the rockers; the detachable bearing caps, also of aluminium alloy, are each secured by four screws. This uncommon construction gives very rigid support to the rockers but was dictated primarily by the difficulty of evolving any other satisfactory method of rocker mounting with hairpin valve springs.
Hollow Journals
As mentioned earlier, the rocker gear is fed from the pressure oil pump; from the union at the rear of the box, the oil enters a longitudinal gallery from which passages lead to the metering holes in the half-bearings.
Oil oozing from the end of the bearings is centrifuged along the rocker arms to the valve-stem ends and push-rod ends.The rockers are 3% nickel-steel forgings, case-hardened all over. In order to provide ample bearing area without excessive weight, the large-diameter journal portion is hollow.
Question: “Although hairpin valve springs have been employed for many years on the racing KTT engines, the new MSS unit is the first Velocette touring engine to be so equipped. What is the reason for this change?”
Answer: “It was found during early experimental work that coil springs would not give us what was required. To get the necessary characteristics with coil springs would have involved overstressing the material. With hairpin springs, the loading can be such as to give a considerably higher stress than is permissible with coil springs. A further advantage in this particular application is that the natural frequency of vibration of the hairpin spring is higher than that of the coil spring which it replaced, so that the possibility of spring surge is eliminated.”
Question: “The springs fit in an upper holder which is separate from the collet collar and is a sliding fit thereon. This practice is unusual in that most other hair-pin spring engines have the collets seating directly in the spring holder. What is the object of your rather more complicated layout?”
Answer: “Our layout is, of course, less simple, and involves a slightly higher reciprocating weight than the alternative you mention, but it is identical with that employed on the KTT engines. The advantage is that the valves can rotate. Freedom to rotate is particularly beneficial to the exhaust valve which is always unevenly heated and so tends to distort. If the valve is free to rotate we have found that it will certainly do so, although we cannot say why; thus it will not always be distorting in the same direction, and permanent deformation is less likely than with a valve which is held.”
Silchrome is used for the inlet valve and an austenitic steel for the exhaust valve. Guides are of aluminium bronze, a good bearing material which has a coefficient of expansion similar to that of the head alloy and so will not tend to loosen when hot. Also the absence of flanges simplifies machining and requires less weight (and therefore cost) of material.
Combustion-chamber Depth
Question: “The piston crown is almost flat, having a radius of 5", and has no cutaways to provide valve clearance. Also the included angle between the valves is 70°, as on earlier engines, so that the combustion chamber is rather shallower than a true hemisphere. What factors affected your decision to adopt this particular combination?”
Answer: “The absence of valve recesses results, of course, from the moderate valve timing employed, although the compression ratio, at 6.8 to 1, is probably above average for this type of engine. We retained the valve included angle at 70° in order to get a fairly open chamber, with adequate depth at the sparking plug; such depth assists propagation of the ignition flame and so ensures good combustion characteristics and freedom from detonation. Having decided on the bore and the size and angle of the valves, the shape of the piston crown followed automatically.”
In the interest of consistency between one engine and another, the inlet port is almost fully machined, so as to leave the minimum amount of hand work and, therefore, possibility of variation in shape. The port has a straight taper from the carburettor flange to the valve guide; this results in a small-radius bend at the bottom of the port which would appear to mask this portion of the valve opening area.
However, Mr. Udall considers that in any engine the area of valve opening at the inside of the port curvature can almost be ignored as regards cylinder filling; in his opinion the aim should be to make the best possible use of the remainder of the area. This is achieved on the MSS by having a layout such that the axis of the straight section of the port, when produced, passes through the area of opening at full lift. In other words, if the eye looks exactly along this axis, it can see straight into the cylinder head, so that the passage for the inlet gases is obviously unobstructed.
On the electrical-equipment side, there is one respect in which Veloce have long ploughed a lone furrow in the motor cycle world, although their method is used on the majority of cars.
Question: “Belt drive to the dynamo has for many years been a feature of Velocette machines and you retain it on the engine under discussion. What do you consider to be the advantages of the system over gear or chain drive?”
Answer: “The belt drive is cheaper than any other form would be, save direct drive as featured with A.C. generators; it is extremely quiet and requires no lubrication. Further, it is more resilient than any positive drive could be without the inter-position of a flexible coupling, and it can slip if overloaded, thereby avoiding damage to the dynamo.”
Search for Quietness
The legislation recently introduced on noise emission in Germany and Switzerland has underlined the rather unsatisfactory position of the motor cycle vis-à-vis the car. Whereas motor cycle exhaust noise is probably more noticeable to the man in the street than is mechanical noise, the latter often predominates as far as the rider is concerned. This thought gave rise to my final question, to round off a most interesting and instructive interview.
Question: “Velocette engines have acquired a name for unusual mechanical quietness, a reputation which, I gather, is maintained by the latest engines. To what features do you attribute this quietness?”
Answer: “As would be expected, the ‘alloy’ engines proved more of a problem than the “iron” engines which had better noise-damping qualities. In consequence we have had to pay more attention to the sources of noise, rather than to damp it out after it had been started. The adoption of taper-roller bearings, as has already been stated, has gained us a little, and the rigidity of the flywheel assembly and close-up support of the timing gears assist towards silence. Ample lubrication, the helical teeth of the timing gears, the belt dynamo drive and careful attention to the profile of the engine-shaft shock-absorber lobes are all contributing factors. In common with other manufacturers, we employ quietening ramps on the cams; but it may not be generally realised that we have been doing so since the ‘twenties.”
In the early post-war years, the model was reintroduced in virtually its 1939 form, but was dropped after 1948; such were the manufacturing difficulties at the time that it was decided to concentrate production resources on the LE and MAC models. In 1951, the MAC engine appeared in a considerably redesigned form, with light-alloy cylinder and cylinder head.
As a result of the easing of manufacturing problems during the last two or three years, and the demand from Velocette adherents for a larger-capacity machine, it was decided to work on a new MSS power unit. In the interests of economic production, the MSS engine would be housed in the newly developed MAC rear-sprung frame, and would embody the proven features of its ancestors together with the lessons learned from the MAC.
Although it bore a similarity to the earlier version, the new MSS engine differed considerably there from in its internal details. Possibly the most obvious change concerned the bore and stroke which, from being 81mm x 96mm, became “square” at 86mm x 86mm. The engine had the familiar high-camshaft operation of the overhead valves, and emerged as a functional and efficient-looking unit
Charles Udall, who was responsible for the design, has been with Veloce, Ltd., since 1927 and, in pre-war years, was on the racing side under the late Harold Willis; on Willis’ death in 1939, Mr. Udall took over the racing department and, after the war, became development engineer. In this capacity he is concerned not only with laying out a design on paper but also with ensuring that it comes up to expectations after its translation into metal- an ideal combination to a technician in search of information.
To after the bore and stroke of a successful engine is a major step, not to be undertaken lightly by any designer. Hence my first query:
Question: “Does the 86mm bore and stroke mean that you are now in favour of comparatively short strokes and big bores, or is some other consideration involved?”
Answer: “The reason for the changed dimensions is very simple. We decided to use the current spring frame to house the new MSS engine, and the size of this frame is such that the old “long-stroke” engine was too tall to go in- so we shortened its stroke until it would fit. Where very high rpm. are necessary, as on a racing engine, a short stroke is essential, but the average roadster engine is in a different category and there is, in my opinion, no intrinsic advantage, in a bore/stroke ratio approaching or exceeding unity. A very tall engine will tend to be heavier than a short one and, if the stroke is over-long, difficulty will be encountered in getting adequate sizes of valves. With in certain limits, however, I consider that I could get almost identical characteristics and performance from any bore/stroke ratio.”
I had expected a technical lecture and had received a straightforward admission of expediency! We then considered the crankshaft assembly, and Mr. Udall pointed out that the flywheels, though comparatively narrow, are of large diameter with rims of fairly deep section, thus providing maximum flywheel effect with minimum weight.
Shallow-Taper Fit
Question: “I notice that there are no nuts for securing the mainshaft or the crankpin in the flywheels. Presumably you employ interference fits, but the absence of nuts is unusual in the case of the crankpin, and represents a difference from the earlier MSS engine. Why have you adopted this particular method of construction?”
Answer: “The mating parts have a taper of 0.008" per inch. This taper enables each shaft to be entered in its hole without difficulty during assembly and gives an interference fir of 0.003" to 0.0035" when fully home-ample for complete security. The elimination of the crankpin nuts has meant that we no longer have to counter-bore the flywheels to accommodate the nuts, and thus have almost twice the length of crankpin shank held in each wheel than we had before. In addition, we have increased the diameter of the shank; the combined effect of the two alterations, plus the reduced throw of the crank, is a very much stiffer flywheel assembly. Incidentally, we have employed the shallow-taper method of construction since 1925.”
It is of the utmost importance that the materials used for the various components of the crankshaft assembly should be up to the loading imposed on them. For this reason, the flywheels are stampings in a 0.3%, carbon steel, the crankpin is a 3 %, nickel-chromium, case-hardening steel, and the drive-side and timing-side shaft a direct-hardening steel is employed.
For the connecting rod En18, a 1% chromium steel, is employed and the forging is heat-treated to 60 tons/sq in tensile strength. The heat treatment is carried out before machining, to avoid distortion, and the usual hardened sleeve is pressed in to form the outer race of the big-end bearing.
Question: “On the ‘iron’ engine you balanced 70% of the reciprocating weight, whereas on the new engine only 55% is balanced. Does this alteration result from the reduced weight of the engine?”
Answer: “While the reduced weight might have had an effect, one cannot say that there is an optimum balance factor for an engine on its own: there is only an optimum factor for a giver engine-and-frame combination, which includes the method of mounting the engine in the frame. Here we have an engine of altered dimensions and weight from the earlier model, housed in a completely different frame. It would have been most surprising had the best balance factor proved to be the same for both machines. There is no known method of forecasting the best balance factor for any particular combination so it has to be ascertained by experiment.”
Interesting comment, as the balance factor was changed back to 70% around the introduction of the Venom in 1956. DQ.
High Load Capacity
The MSS engine is probably unique in that it has taper-roller bearings to support the mainshafts, in place of the more usual ball or parallel-roller pattern. These taper-roller bearings were first introduced on the post-war “long-stroke” MSS engine and proved so satisfactory that they were retained in the new design.
Bearings of this type have a high load-carrying capacity for their size, and are less affected than are other varieties by out-of-line forces caused by shaft deflection, which cannot be completely avoided in any engine. Also, the taper-roller bearing is intended to withstand axial as well as radial loading and so is admirably suited to dealing with the end-thrust imposed by the helical timing gears.
With quiet operation in mind, a degree of pre-loading is applied to the main bearings; this “nip”, as it is called, is not in any way harmful to the bearings. It ensures absence of play between rollers and races, so that “grumbling” during running is avoided.
The inner races are pressed on to the mainshafts. The outer races are pressed into the crankcase halves, where they are shimmed to provide a nip of 0.004" when the engine is cold. At normal running temperatures this nip comes down to between ½ and ¾ thou. It is recommended by the makers that after 10 to 15,000 miles, by which time the bearings will have thoroughly bedded down, the crankcase should be dismantled and the outer races re-shimmed to restore the pre-loading to its original figure. Thereafter no further attention should be necessary for the rest of this life of the bearing.
Question: “In this new engine you retain the traditional, narrow crankcase, with only one bearing for each mainshaft. Since so many other manufactures employ two bearings, at least on the drive side, can you tell me the reasons for your layout?”
Second Bearing Unnecessary
Answer: “Many years ago we decided to keep the primary chain line as close as possible to the engine centre line. This necessitated our putting the primary drive inside the final drive. Although this feature resulted in a more complicated clutch-operating mechanism, the absence of overhang and the consequently short, stiff mainshaft enabled us to dispense with a second drive-side main bearing which would undoubtedly be necessary if we had a conventional drive layout. On the timing side, the mainshaft pinion is located right up against the outside of the bearing, so that here, too, the shaft is short and stiff enough to require no out board support.”
Question : “For the big-end bearing you employ a single row of 3/16" x 9/16" rollers in a Duralumin cage, in place of the more common two rows (or even three) of shorter rollers. What benefit do you consider to accrue from the use of these long rollers?”
Answer: “All bearing rollers have radiused- or chamfered-ends, to avoid flaking of the case at these points. These end radii reduce appreciably the effective length of the roller, so that three rows of 3/16" x 3/16" rollers would have a lower bearing capacity than has our single row. You will note that the ends of the cage which runs on the crankpin, are located in shallow recesses in the flywheels, so that the rollers virtually fill the gap between the wheels. This avoidance of wasted width assists in achieving a narrow rigid crankshaft assembly.”
Engine lubrication is by gear-type pump driven by a bronze worm on the end of the timing-side mainshaft; to ensure through scavenging of the crankcase, the scavenge-pump capacity has been increased and is nearly two and a half times that of the pressure side.
On leaving the pump, the oil is forced to a gallery in the timing cover, whence it passes to four separate feeds: one leads to a big-end bearing via the mainshaft, another lubricates the cam-spindle bearing, the third directs oil to the cam faces, and the last takes oil to the rocker gear. Oil is supplied in the desired quantity and at a suitable pressure for each duty by means of jets and metering holes.
Several features requiring comment emerged from a study of the lubrication system, so I put the following questions to Mr. Udall.
Non-return valve
Question: “A disadvantage of the gear-type oil pump is its tendency to let oil seep past it into the crankcase, so that over-oiling can result on starting after the engine has not been running for some time. Have you made any provision to deal with this difficulty?”
Answer : “We encountered the trouble on earlier engines, and have taken two steps to eliminate it on the MSS unit. In non-return ball valve, held on its seat by a light spring when the engine is not running. Pump suction is sufficient to take the ball off its seat so that oil can flow from the tank to engine. Though unusual, this method has proved entirely satisfactory, provided only that the feed pipe is fully primed with oil before it is coupled to the tank. On the scavenge side, the oil is returned through a fabric filter in the tank and, to prevent the oil in the filter from draining back, the return pipe is extended above the top of the filter.”
Improved Lubrication
Question: “Big-end lubrication on the earlier engines was by the usual drill ways in mainshaft, flywheel and crankpin, but I note that the crankpin is no longer drilled. Instead, the drill way in the flywheel is inclined and emerges at the inner face slightly nearer to the centre than the crankpin. What is the advantage of this over the former method?”
Answer: “Where the crankpin is drilled axially, centrifugal force results in the oil tending to go only to the outer part of the bearing, so that the rollers nearer the axis of the flywheel may be under-lubricated. By supplying the oil to the point of the bearing nearest to the centrifuged through the whole of the bearing, so that more through lubrication is obtained.”
Question: “The rocker gear is fed from the pressure side of the oil pump, and not from the scavenge side as on many other engines popular today. Also, the pipe from the timing chest is no less than 5/16in in outside diameter. Why do you not lubricate from the scavenge pump, and why is the pipe so large?”
Answer : “Lubrication from the scavenge pump may result in some restriction in efficiency and hence inadequate scavenging. Also the pressure is so low that, in conjunction with a fair length of small-bore piping, little real lubrication can result, particularly when the oil is cold.
“We prefer to use the pressure pump to make sure the oil gets to where it is wanted, to give it passages of adequate size through which to flow, and to restrict the quantity by the use of metering holes at the component in concerned-in this case the rocker bearings, where the oil emerges through 0.046" holes.
Another feature to be carried on unchanged from the earlier-series engines is the timing gear. All push-rod Velocette engines have had small-pitch, helical-cut teeth in the timing train; despite their rather higher manufacturing cost, such gears are considered to be well worth while since they operate more quietly than do straight-toothed gears. The reason for this quieter running is that more than one tooth is always in full engagement over part if its length; thus, the driving load is not transferred suddenly from one tooth to the next but the changeover is relatively gradual and smooth.
Adjustment of Backlash
A diametral pitch (number of teeth divided by pitch circle diameter) of 32 is employed, and the intermediate idler gear between the crankshaft pinion and the cam wheel has a hunting tooth to distribute wear. This idler also has an adjustable mounting whereby backlash can be taken up-a further point making for quiet running. The fixed spindle on which it revolves has a circular back plate with three tapped holes; there are three similarly spaced holes in the crankcase wall through which pass the set-screws securing the back plate. Adequate clearance is allowed in these second three holes to give the necessary meshing adjustment which is held when the screws are tightened. On erection, the adjustment is set so that all backlash is just taken up with the engine cold.Spindle Support
As mentioned earlier by Mr. Udall, the mainshaft pinion is carried close up to the main bearing. It follows that the intermediate and cam gears also have little overhang from the crankcase wall; both are bronze bushed, and the cam spindle is pressed into the case. An outboard steady plate supports the outer ends of the two gear spindles and that carrying the cam followers. The steady plate is tied to the crankcase at two points, and thus not only maintains the spindles in correct relation with each other but also with the crankshaft.
The taper-interference fit mentioned in connection with the crankpin and mainshafts is also found between the cam wheel and the sleeve on which the cams are formed. In this case the taper that the parts are self-gauging: if the fit is correct, the sleeve will enter exactly half-way through the wheel when inserted by hand. If it went less far, the interference fit on pressing it home would be too heavy, while entry beyond the halfway point would result in too light an interference.
Question: Compared with that of many other engines, the valve timing of the MSS engine is very ‘moderate’ and provides only 38 degrees of overlap. This reduction from the 60 degrees of earlier MSS engines was presumably made with a view to economy and good torque lower down the speed range. Has any serious loss in top-end performance resulted and, if not, how have you avoided the loss?”
Increased Radius
Answer: “ You are right in your assumption that we were guided primarily by the need for economy and better low speed pulling. However, there is no serious loss at the top, as is indicated by the peak power output of 23b.h.p. at 5,000rpm, with air cleaner and standard silencer. We have obtained this peak performance by an alteration to the bottom rockers (cam followers). These rockers have a radius of 1" instead of 3/8" as with the former engine. This larger radius results in quicker acceleration of the valve off its seat, and a longer deceleration period towards full lift.
“With a fairly high valve lift, the deceleration period must be as long as possible if the valve mechanism is going to follow the cam motion at high rpm. which it must do if float is to be avoided. Softer timing means that the total period available for opening (or closing) the valve is lessened, so that only by speeding up the acceleration stage was it possible to maintain an adequate valve lift with the new timing.”
While the fuel consumption under road conditions must await an independent road test, Charles Udall is confident that the MSS will prove economical. The effect of the modified valve timing on the torque curve has been most marked. Although the actual torque peak occurs as before at about 4,000 rpm the torque is very nearly constant between 3000 and 4,500rpm. after which it falls off rather sharply. Since the torque figure is still good at as low as 2,500 rpm. it should obviously be possible to drive the MSS largely as a top-gear machine if desired, and it should have excellent characteristics for sidecar work.
The cam followers referred to by Mr. Udall are of 3% nickel, case hardening steel and have a hard-facing alloy in the rubbing radius. Push rods are of Duralumin tubing with hardened steel ball-ends pressed into the lower ends.
Checking the Clearance
An unusual arrangement is employed at the rocker adjusters. The rocker carries a threaded, ball-end adjuster which seats in a cup formed in a hardened-steel mushroom. The stem of the mushroom is a sliding fit in the bore of the push rod, and the underside of its head forms a flat shoulder. On to the end of the push rod is pressed a shouldered sleeve; the shoulder of the mushroom seats on the flat top face of this sleeve.It will be evident that the clearance between shoulder and sleeve face will be a measure of the valve clearance, which is checked by sliding a feeler into the gap. The adjacent corners of sleeve and mushroom have a small radius to assist the insertion of the feeler.
Apart from improved accessibility, this adjustment scheme has an advantage over a threaded adjuster at the valve end of the rocker. The thrust button which bears on the valve can be radiused in one plane only instead of being part-spherical. The resulting line contact causes less wear of the valve stem than did the almost point contact of the part-spherical button employed for the earlier engine.
Holding-down Studs
When redesigning the MAC engine, Y-alloy was adopted for the cylinder head on account of its mechanical strength and its good heat conductivity. The latter feature permits the use of a higher compression ratio than does cast iron, thereby improving both performance and fuel consumption. Since it was clearly desirable that the MSS should not lag behind in these two respects, Y-alloy forms the head material on this engine also.
Shrunk into the head are valve seats of austenitic iron. This material was chosen because of its resistance to impact loading at elevated temperatures, and because of the security it provides through having a coefficient of expansion approaching that of Y-alloy. Four long holding-down studs pass through the head and the upper fins of the Al-fin cylinder barrel, and these studs gave rise to my next point
Question: “The four cylinder and head holding-down studs screw into steel sleeves which in turn screw into the crankcase. Surely such sleeves are unnecessary with semi-permanent items such as the studs?”
Answer: “They would be unnecessary if the studs were semi-permanent, but the height restriction of the frame is such that the studs have to be removed before the head can be lifted. Removal of the head will normally be infrequently required, but we thought it as well to guard against the inveterate “dismantler” by ensuring that no crankcase threads would strip.”
An unusual detail is that the head holding-down nuts have nylon inserts which, in addition to being self-locking, seal the threads against oil leakage from the head and down the studs.
On top of the head is bolted the rocker box, a die-casting in DTD424 aluminium alloy. Two half-bearings are machined in the box to take the journal portion of the rockers; the detachable bearing caps, also of aluminium alloy, are each secured by four screws. This uncommon construction gives very rigid support to the rockers but was dictated primarily by the difficulty of evolving any other satisfactory method of rocker mounting with hairpin valve springs.
Hollow Journals
As mentioned earlier, the rocker gear is fed from the pressure oil pump; from the union at the rear of the box, the oil enters a longitudinal gallery from which passages lead to the metering holes in the half-bearings.
Oil oozing from the end of the bearings is centrifuged along the rocker arms to the valve-stem ends and push-rod ends.The rockers are 3% nickel-steel forgings, case-hardened all over. In order to provide ample bearing area without excessive weight, the large-diameter journal portion is hollow.
Question: “Although hairpin valve springs have been employed for many years on the racing KTT engines, the new MSS unit is the first Velocette touring engine to be so equipped. What is the reason for this change?”
Answer: “It was found during early experimental work that coil springs would not give us what was required. To get the necessary characteristics with coil springs would have involved overstressing the material. With hairpin springs, the loading can be such as to give a considerably higher stress than is permissible with coil springs. A further advantage in this particular application is that the natural frequency of vibration of the hairpin spring is higher than that of the coil spring which it replaced, so that the possibility of spring surge is eliminated.”
Question: “The springs fit in an upper holder which is separate from the collet collar and is a sliding fit thereon. This practice is unusual in that most other hair-pin spring engines have the collets seating directly in the spring holder. What is the object of your rather more complicated layout?”
Answer: “Our layout is, of course, less simple, and involves a slightly higher reciprocating weight than the alternative you mention, but it is identical with that employed on the KTT engines. The advantage is that the valves can rotate. Freedom to rotate is particularly beneficial to the exhaust valve which is always unevenly heated and so tends to distort. If the valve is free to rotate we have found that it will certainly do so, although we cannot say why; thus it will not always be distorting in the same direction, and permanent deformation is less likely than with a valve which is held.”
Silchrome is used for the inlet valve and an austenitic steel for the exhaust valve. Guides are of aluminium bronze, a good bearing material which has a coefficient of expansion similar to that of the head alloy and so will not tend to loosen when hot. Also the absence of flanges simplifies machining and requires less weight (and therefore cost) of material.
Combustion-chamber Depth
Question: “The piston crown is almost flat, having a radius of 5", and has no cutaways to provide valve clearance. Also the included angle between the valves is 70°, as on earlier engines, so that the combustion chamber is rather shallower than a true hemisphere. What factors affected your decision to adopt this particular combination?”
Answer: “The absence of valve recesses results, of course, from the moderate valve timing employed, although the compression ratio, at 6.8 to 1, is probably above average for this type of engine. We retained the valve included angle at 70° in order to get a fairly open chamber, with adequate depth at the sparking plug; such depth assists propagation of the ignition flame and so ensures good combustion characteristics and freedom from detonation. Having decided on the bore and the size and angle of the valves, the shape of the piston crown followed automatically.”
In the interest of consistency between one engine and another, the inlet port is almost fully machined, so as to leave the minimum amount of hand work and, therefore, possibility of variation in shape. The port has a straight taper from the carburettor flange to the valve guide; this results in a small-radius bend at the bottom of the port which would appear to mask this portion of the valve opening area.
However, Mr. Udall considers that in any engine the area of valve opening at the inside of the port curvature can almost be ignored as regards cylinder filling; in his opinion the aim should be to make the best possible use of the remainder of the area. This is achieved on the MSS by having a layout such that the axis of the straight section of the port, when produced, passes through the area of opening at full lift. In other words, if the eye looks exactly along this axis, it can see straight into the cylinder head, so that the passage for the inlet gases is obviously unobstructed.
On the electrical-equipment side, there is one respect in which Veloce have long ploughed a lone furrow in the motor cycle world, although their method is used on the majority of cars.
Question: “Belt drive to the dynamo has for many years been a feature of Velocette machines and you retain it on the engine under discussion. What do you consider to be the advantages of the system over gear or chain drive?”
Answer: “The belt drive is cheaper than any other form would be, save direct drive as featured with A.C. generators; it is extremely quiet and requires no lubrication. Further, it is more resilient than any positive drive could be without the inter-position of a flexible coupling, and it can slip if overloaded, thereby avoiding damage to the dynamo.”
Search for Quietness
The legislation recently introduced on noise emission in Germany and Switzerland has underlined the rather unsatisfactory position of the motor cycle vis-à-vis the car. Whereas motor cycle exhaust noise is probably more noticeable to the man in the street than is mechanical noise, the latter often predominates as far as the rider is concerned. This thought gave rise to my final question, to round off a most interesting and instructive interview.
Question: “Velocette engines have acquired a name for unusual mechanical quietness, a reputation which, I gather, is maintained by the latest engines. To what features do you attribute this quietness?”
Answer: “As would be expected, the ‘alloy’ engines proved more of a problem than the “iron” engines which had better noise-damping qualities. In consequence we have had to pay more attention to the sources of noise, rather than to damp it out after it had been started. The adoption of taper-roller bearings, as has already been stated, has gained us a little, and the rigidity of the flywheel assembly and close-up support of the timing gears assist towards silence. Ample lubrication, the helical teeth of the timing gears, the belt dynamo drive and careful attention to the profile of the engine-shaft shock-absorber lobes are all contributing factors. In common with other manufacturers, we employ quietening ramps on the cams; but it may not be generally realised that we have been doing so since the ‘twenties.”
Acknowledgement is made to Morton's Motorcycle Media who hold copyright to items from "The Motor Cycle" and "MotorCycling".
Left click on images to enlarge.
Friday, August 15, 2008
During the late 1940s and into the early 1950s, employees of P & R Williams Pty Ltd, the
NSW Velocette distributors had a fishing weekender on the beach at Tea Gardens north of Sydney..actually is was one of the numerous shacks built at the time on the sand dunes behind the beach, either unknown to the local government authorities or ignored by them.
Fishing was great at the time...check out the size of the fish in the photos and of course the beach was long, miles of sand and transport needed to get to the best fishing spot that day...accordingly Dave Jenkins and Don Bain fitted special rims to the rear of some motorcycles, utilising car tyres which traversed the loose sand well.
Don Bain and Dave Jenkins were champion motorcycle racers and both won title events at the annual Easter Motorcycles races at Bathurst NSW.
Interesting specials.....
Left click on the images to enlarge.
.
Tuesday, August 12, 2008
Important Safety Notice: Safety Recall on all 2006 Honda TRX450R and TRX450ER ATV models due to contaminated ball joint.
This recall notice only pertains to vehicles within the following VIN Ranges:
JH2TE320*6K000019 to JH2TE320*6K010997 (TRX450ER)
JH2TE324*6K000007 to JH2TE324*6K000111 (TRX450R)
*: Denotes check digit
A safety defect may exist in the steering system of your TRX. The front suspension arm ball joints may have been contaminated during the production process, resulting in rapid wear of the ball joints and possible ball joint separation. If ball joint separation occurs while riding, the TRX could lose steering control and may crash.
What should you do?
Honda strongly recommends that you do not operate your TRX until it has been repaired. Parts will be available soon. We will send you another letter notifying you when you can go to your Honda ATV dealer for the free replacement of all four front suspension arms
(Right/Left & Upper/Lower).
As I mentioned in my first foray into pen and ink drawings from the motorcycle media, graphic art has changed dramatically …. lets have another look into 1931 and 1933 when graphic 
,Jock+Leyden.1933-1.jpg)
artists, cartoonists and the like, armed with pen, ink and pencil recorded the images of the day in concert with the film camera.
Acknowledgement is made to Mortons Motorcycle Media owners ofthe copyright for 
"The Motorcycle" and "MotorCycling" and to the families of the artists for use of the images.
Left click on images to enlarge.
Sunday, August 10, 2008
I’ve owned several specials…motorcycle specials and Velocette ‘s in particular in my motorcycling career and these are two 
that come to mind and which I have photographs of.
But before we go on, what is a special?
I guess I’ll define it as a motorcycle made up of components that were not constructed together when the motorcycle was first built, in my case, in the Velocette factory. In Australia we could term this “ a bastard”…….
Pictured in the pits at Amaroo Park raceway around 1977, with reverse cone megaphoned exhaust. I often switched between a straight pipe and a megaphone.
The first was a Velocette racer…unsure of the exact date I got it from a previous owner, Dave Potts, who at the time was working for the Jaguar car distributorship, Bryson Motors , in their workshop.
I would have acquired it likely in the late 1970s and recall Dave telling me it won the 350 class of the NSW Hill Climb championships at Foley’s Hill, near Ingleside and that he also rode it at Mt. Druitt circuit, west of Sydney.
Bill Purnell was believed to have had the frame made for him, possibly in 1954. It was sold on to Leo Schemello who raced it at Mt. Druitt and Bathurst , NSW. He was reputed to “…have either won or was highly placed in the Clubmans events at Bathurst…”.
The first was a Velocette racer…unsure of the exact date I got it from a previous owner, Dave Potts, who at the time was working for the Jaguar car distributorship, Bryson Motors , in their workshop.
I would have acquired it likely in the late 1970s and recall Dave telling me it won the 350 class of the NSW Hill Climb championships at Foley’s Hill, near Ingleside and that he also rode it at Mt. Druitt circuit, west of Sydney.
Bill Purnell was believed to have had the frame made for him, possibly in 1954. It was sold on to Leo Schemello who raced it at Mt. Druitt and Bathurst , NSW. He was reputed to “…have either won or was highly placed in the Clubmans events at Bathurst…”.
Tony 'Ace' Hatton aboard the MAC at Bathurst 1978, I rode my Mk.8 KTT.
The frame was made in Sydney by Stan “Nugge” Smith, one of likely only 20 or so he made, mostly for Velocettes, and was a copy of the frame made in the UK by Doug St. Julian Beasley…more commonly known as Doug Beasley.
This came about by Sid Willis, the well known Australian 250cc racer, famous for his racing Velocettes, usually ex-works stuff.
This came about by Sid Willis, the well known Australian 250cc racer, famous for his racing Velocettes, usually ex-works stuff.
Sid was of small statue, under 5’ tall and “…less than 8 stone weight wringing wet…”, the perfect lightweight rider…
Sid went overseas in 1953 with Tony McAlpine to ride in the IOM TT and various Continental races meeting. He took a rigid framed 250cc DOHC Velo racer, with a cylinder head and cam box from the 1936 factory Velocette racing effort.
Sid went overseas in 1953 with Tony McAlpine to ride in the IOM TT and various Continental races meeting. He took a rigid framed 250cc DOHC Velo racer, with a cylinder head and cam box from the 1936 factory Velocette racing effort.
After a meeting in Europe it became painfully obvious his bike was quick , but didn’t handle well on the cobble stone circuits then common at that time. Arriving in England, he visited Doug Beasley and a frame was made for him and he “debuted” it in the Lightweight 250cc TT in IOM.
Sid did about 5 practice laps in all and in the race finished 5th, the first privateer behind factory runners.
Towards the end of the European tour he and Tony entered for a hill climb in Freiberg, Germany. Sid crashed heavily and bent the frame. On his return to Sydney, he visited “Nugge”, who built a jig off the frame, then ( to Sid’s dismay) cut up the frame to see the tube thicknesses and construction. The first frame off the jig went to Sid and still exists in NSW today. “Nugge” never numbered the frames, so the exact number made and where mine was in the sequence remain a mystery.
Sid did about 5 practice laps in all and in the race finished 5th, the first privateer behind factory runners.
Towards the end of the European tour he and Tony entered for a hill climb in Freiberg, Germany. Sid crashed heavily and bent the frame. On his return to Sydney, he visited “Nugge”, who built a jig off the frame, then ( to Sid’s dismay) cut up the frame to see the tube thicknesses and construction. The first frame off the jig went to Sid and still exists in NSW today. “Nugge” never numbered the frames, so the exact number made and where mine was in the sequence remain a mystery.
The front forks are from an LE Velo, with MAC Velo dampers inside. The engine is basically a MAC, with a special cylinder head, cast in “Y” alloy aluminium , by Sid, for Ted Carey ( another 
well known Australian tuner, who built his own DOHC based MOV in 1948…this for a later blog…)…the so called “Carey Head”. Again a small number were cast, but how many also is unknown, however four different ones have passed through my hands.
It was a light little racer…I weighed it, with an alloy rims front and back it was 265lbs. The engine was 11.5:1 comp. ratio on Methanol and quite successful in the latter day historic racing. MACs on “fuel” really “jump” out of corners and are hard to beat on twisty shorter circuits. On longer circuits OHC/DOHC engined racers tend to run them down.
well known Australian tuner, who built his own DOHC based MOV in 1948…this for a later blog…)…the so called “Carey Head”. Again a small number were cast, but how many also is unknown, however four different ones have passed through my hands.It was a light little racer…I weighed it, with an alloy rims front and back it was 265lbs. The engine was 11.5:1 comp. ratio on Methanol and quite successful in the latter day historic racing. MACs on “fuel” really “jump” out of corners and are hard to beat on twisty shorter circuits. On longer circuits OHC/DOHC engined racers tend to run them down.
I took it over to the second Pukekohe Classic races in NZ in 1981, set up as a 250cc MOV.
It still races in the hands of it’s current owner, Sydneysider Colin Pitcher.
The other special pictured is a bike I still own and resides in the Los Angeles area of California. Built in about 1975 by a Canadian, the late Harry Muckalt in the Vancouver, B.C area, it passed into my hands in the late 1990s and has been used by me on numerous North American Velo OC Nat.
Rallies and rides. In fact I rode it at the 2008 US VOC Spring Opener in May.
Based on a 1960 Velo scrambler frame, with 1948 KSS Mk.2 engine with Amal 10TT9 carb. and "TT" ratio gearbox ( that is it had KTT mk.8 internal gear ratios), MAC petrol tank and Velo Thruxton front and rear wheels it is “ a nice bit of kit” as Sam Jowett, Canadian US VOC member is won't to say…I really enjoy riding it.
DQ pictured "fettling" the KSS special at the 2005 US Centenary Velocette Rally.It still races in the hands of it’s current owner, Sydneysider Colin Pitcher.
The other special pictured is a bike I still own and resides in the Los Angeles area of California. Built in about 1975 by a Canadian, the late Harry Muckalt in the Vancouver, B.C area, it passed into my hands in the late 1990s and has been used by me on numerous North American Velo OC Nat.
Rallies and rides. In fact I rode it at the 2008 US VOC Spring Opener in May.Based on a 1960 Velo scrambler frame, with 1948 KSS Mk.2 engine with Amal 10TT9 carb. and "TT" ratio gearbox ( that is it had KTT mk.8 internal gear ratios), MAC petrol tank and Velo Thruxton front and rear wheels it is “ a nice bit of kit” as Sam Jowett, Canadian US VOC member is won't to say…I really enjoy riding it.
Left click on images to enlarge.
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