CrankshaftsThe Villiers crankshaft is one of the half circle types (hammer head) and saw service in both sizes of engine throughout their manufacture, the only difference being the length of the conrod, 5¼" for 197 and 5½" for the later 250. Non sporting cranks used a crowded double row big end bearing of 26 x ¼" by ¼" rollers, and this was upgraded to a caged bearing of 9 off ¼" by 5/16" for the sports variants. The standard conrod will benefit from an increased oil supply, which is achieved by grinding notches in the big end eye faces. Four indentations on each face, 1 mm deep.
All Villiers crank pins are the same diameter, at 0.7980" to 0.7983" regardless of the type of big end bearing fitted, but the con rod eye size changed to give the caged bearings of the sports variants extra clearance. 1.2981" to 1.2986" for the uncaged bearing, and 1.2985" to 1.2990" for the caged type. This size was increased to 1.2991" to 1.2996" for the A series motors.
The Villiers crankshaft was notoriously weak and twisted quite badly at the first hint of a power increase. A measure of this flexibility can be gained from the factory maintenance and repair manual, in which it states that if reconditioning the original flywheel assembly, an oversize (1 thou) crankpin and rod must be used. Presumably to take up the slack in the elastic flywheels, a sad state of affairs which is not tolerated today in high speed two stroke motors. To counter this problem Alpha came up with a superior replacement shaft which fitted straight into the Villiers cases, this item being used quite extensively by many works teams of the sixties, for it solved their twisting problems.
The Alpha crankshaft had full circle flywheels with reduced crankcase wall clearance (see Fig 5 ) which not only added rigidity but also increased the primary compression ratio, which aided cylinder filling. Designed as a flywheel effect shaft the Alpha crank did not need the Villiers heavy external flywheel, but in the trials application with the flywheel and the extra weight of the additional ring, the better cylinder filling increased plonkability markedly. With the Alpha shaft came a streamlined conrod (of both lengths) and a superior racing type bigend bearing, but the small end remained bushed as in the Villiers rod. The very early rods had a big end width of 0.5", and a single diameter pin, which ran in parallel flywheels. This was later to be increased to 16 mm, the flywheels being machined away around the pin to accommodate the stepped pin, larger bearing and thrust washers. Much of the increased rigidity came from the larger crank pin of the early type and the later stepped crank pin which was needed for the larger big end bearing which now measured 25 x 32 x 16 mm. The outer diameters of the stepped crank pin are not the same size as the Villiers pin, therefore rods and cranks are non interchangeable without recourse to machining, so measure up the fit if mixing Alpha shaft rods with the Villiers webs.
For those who prefer more modern technology, Competition Classics again come to the rescue by providing an "Alpha" type crankshaft available with racing conrod which has a 22_mm Small End eye to take a 22/18 mm needle race for a Japanese piston with an 18mm gudgeon pin, see Appendix E for possible suitable and compatible pistons.
Big end Details
A better crankshaft is available from Invader Kart engines, which again is full circle with a racing type bigend bearing (of Japanese origins) that features nitrided thrust washers. The rod is of an H section and features a crowded needle roller small end with extra thrust washers, but is only available in the 197 length. The shaft is slightly different in that it has an increased diameter for the drive side inner bearing, but is still compatible with the Villiers cases if the bearing is replaced. As the timing side shaft is machined to take a Motoplat rotor, this system must be used as the Villiers item will not fit the taper.
Some years ago the kart racers tried to break away from the long stroke stigma attached to the 9E, and experimented with the 63.5 mm stroke crankshaft from the 2L 175 cc engine, in conjunction with a 63 mm piston from the 225 cc 1H engine. This combination ended up at an over square 198 cc, which made it rev better. The 175 crank was of the full circle type, which used the same main bearings, and upped the primary compression ratio, on to this was fitted the shortened 225 piston in a bored out 9E cylinder, the top of which had been machined off to restore the correct piston deck height. In this application only, the ports were then modified and enlarged to match the reduced stroke. This was an improvement by the standards of the day, but it was stuck with the Villiers crankshaft. The basic techniques remain the same but the metallurgy, oil, and our expectations have moved on. Competition Classics have 68 mm stroke cranks to use with 68 mm Starmaker cylinders, at a quality that supports our expectations.
Main bearings, again adequate for normal functioning, require some beefing up for high speed work. The drive side bearings need to be replaced by high speed fibre caged types and separated by a larger diameter alloy spacer, again to increase crankcase compression. The length of the spacer sets the crank central within the cases, so to ensure equal clearance between crank wheels and cases, shim up or machine down the spacer to suit. Many experiments were carried out in the early days to increase reliability, one of which was to place the drive side oil seal inboard of the outer drive side bearing. A pair of oil seals placed back to back were inserted into the space between the two bearings, running on the original spacer, this left the outer bearing to gain its lubrication from the primary chain case. The idea was good, and used in the Starmaker engines from 1963, but the debris floating about in the chaincase must have shortened the bearing life some what.
The timing side bearing originally of the single roller type (R125), can be replaced by a double ball race (3205 or 4205). As the double bearing is 5 mm thicker, the retaining circlip is deleted so that the bearing sits tighter into the shaft, but make sure that the oiling hole is unrestricted, if it is then redrill. The absence of a circlip to restrain the bearing is a possible source of trouble, if the bearing is not a captive fit at working temperatures. The bearing could move and damage the oil seal, or worse, could persuade the inner timing casing to work loose, which in turn would damage the ignition. It is possible to use double row bearings on both sides if you can machine the drive side crankcase and reduce the thickness of the bearing spacer. Use drive side outer: 4204, drive side inner 4304, timing side 4205.
If the flywheel is to be retained it should be inspected closely around the area of the central boss. On early flywheels the steel central boss was riveted to the brass wheel, which was quite satisfactory, but the later competition types with the extra weighted ring, were held together with countersunk Allen screws. These later types have a habit of unscrewing themselves, and should be assembled with a heavy duty thread locking agent.
When the Greeves Silverstone was first introduced it was recommended that the crank seals were changed after every meeting, as the wear rate was so high on the racing engine. The modern solution is to use Teflon coated oil seals. Before the times of Teflon coatings, Brian Woolley came up with an answer that not only worked but increased the time between servicing. His method entailed the use of Honda C50 piston rings to form labyrinth seals in place of the rubber seals. The rings were held in position by a steel sleeve which was a press fit into the crankcase, running in a slotted alloy carrier that rotated with the crank, the rings stopping any gas flow much in the same way that they do on the piston. As the seals on the standard 9E cases are smaller than the Greeves cases this modification may be a difficult one to embody without resorting to machining the seal housings, but for someone with machining know how it may be a feasible project. On the drive side the labyrinth seal can be located between the two bearings, the slotted carrier doubling as the bearing spacer. The original rubber seal can be left in position, and the outer bearing fed with lubricant from an external reservoir, or fed from the primary chaincase. The same technique can be employed on the timing side, if the 11E double bearing set up is used.
Seals do not last for ever, even the Teflon coated variety, so if the engine starts to run weak for no reason, test the effectiveness of the seals with a pressure tester. The tester bolts on over the piston in place of the cylinder, or may be much smaller and require the removal of the piston, and is pumped up to 10 psi. The working pressure of the engine is in the region of 6-7 psi, so if the pressure drops below this value quickly, then suspect the seals. To verify a leak use Fairy Liquid and watch for bubbles.
When the 9E was designed the criteria was for the big end to be restrained in its horizontal plane and to let the small end float on the gudgeon pin. This practice restricts the flow of lubricant to the big end bearing, hence the need to provide extra oiling passages to the bearing when using the standard set up. Modern thinking has gone the other way, in that it now restrains the less stressed small end, and lets the big end find its own centre. The Invader rod does just this, employing thrust washers to centralise the rod in the piston, which positions the big end in the centre of its 50 thou clearance, which in turn allows a free flow of lubricant.
Both authors use Castrol R40 or Morris MLR40 at a ratio of 25:1 as a lubricant, not because they are traditionalists, but because it is the only oil they have found to cope with the rigours of racing a heavily tuned 197 or 250. They work well, even promoting the well being of a big end bearing that can have up to 2 thou wear, with no problems. The authors have seen other riders use synthetic oils at 40:1 with unsatisfactory results. Use of synthetic oils in modern liquid cooled motors is recommended, but not, please, in 30 year old motors.
Dismantling the crankshaftIt should be dismantled and rebuilt for the start of each season, and will last for at least 20 days of racing or enduro, but depending on your activity, this may not be an entire season especially if you include test days and practise sessions. A crankshaft rebuild should last at least two seasons under trials conditions, and 10,000 miles on the road.
To dismantle a crank you need a 10 ton press. The ideal is that there should be no detectible longitudinal play in either big end or small end bearings while clean and dry. Some small amount of movement is acceptable if you use Castrol R, say 2 thou maximum. The Villiers cranks use side shims on the bigend pin to restrict the side to side movement of the conrod to within 20 thou or so, some movement is clearly required to allow the oil an easy entry path. The modern Honda MX machines seem to shim the conrod at the smallend to virtually no end float at all, and leave the bigend to float without shims or restraint.
An example of what can happen is John's racing crank which was perfect at the start of the 1993 season, and finished with 2 thou movement at the end of the season. He was really lucky to finish as the ground bearing surface of the crankpin was missing from the underside of the pin, and this missing material gave the 2 thou play vertically up and down, but at 90o there was no play at all. Some cranks take a stepped 20/22 mm pin, others take a straight 22 mm crankpin, the author slightly prefers to use 22_mm Yamaha pins rather than Villiers components, what ever the pin choice, it should need over 2 tons to push the pin in, much less than 2 tons and get an oversize crankpin. With an oversize pin and a new bearing, the rod may no longer fit, so you need a selection of good condition rods with different amounts of wear.
Putting a crank back together again is a difficult and time consuming job unless you have the knack for it. The crank is assembled in a vice to start with and later in a press, and must be so that the crank halves are exactly in unison on the crankpin. Start by nipping up in the vice and then check by rule and eye to see if they are in line and reasonable square. Now use the vice to press the pin in some 2 mm into the crank and check more accurately. This is your last chance to get it right, when the flywheels are pressed together it will take an awful lot of effort to move them even by 1o so you had best not be 5o out. A simple way to check is to use a square set block and rule, with the block along one flywheel the rule should touch the edge of both flywheels at the circumference, check in 6 or 8 positions.
This chapter is continued in the book with the following major sections.
Principle of static and dynamic balance