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one major reason for heavy clutch lever action on Commandos is because Norton / NVT employed FOUR different versions of the diaphragm spring during Commando production each new one thicker and 'stronger' than the previous one which not only increased the load being applied to the clutch friction interplates which increased the amount of torque the fully engaged clutch would transmit before slip occured in a FAILED effort to cure the very serious clutch slip problem Commandos were plagued with but which also increased the amount of 'grunt' required to operate the clutch lever...... The tale is as follows.......
The ORIGINAL Commando clutch was CORRECTLY designed as a DRY clutch and with its original 0.075 inch thick spring applying approx 380 lbf clamp load to the clutch plates it would NOT suffer slip problems even when the MAXIMUM crank torque output was shoved through it. It was also EASILY operated with no more than two fingers all day long and did not suffer from drag problems either. One early 750 road tester wrote ' I find it incredeble that such a delightfully light and positive clutch could of been ignored by motor cycle manufacturers for so long before being introduced on the Commando '. Clearly he had forgotten the earlier DRY diaphragm spring clutches designed for the Villiers Starmaker motors, single and twin friction plate versions each with slightly different springs the clutches and springs being designed by Mr Peter Senior who was when I first contacted him many years ago the Laycock Engineering of Sheffield Chief Clutch Designer and Engineering Director. The two Starmaker springs being shown on the Laycock Engineering drawing as 83466 Ref 10 and Ref 20. One 0.076 thick and the other 0.073 inch thick both givcing different clamp loads.
The original 0.075 inch thick Commando spring was 83466 Ref 30 and CORRECTLY set up as it was designed to be set up with the clutch fully engaged with new friction plates fitted it applied a clamp load to the plates of approx 380 lbf.
Unfortunately Norton or whatever they were called at the time shoved a designed to be run DRY clutch into an oil bath CHAIN case as Norton had done since introducing their pressed steel oil bath CHAIN case way back in the early 1930s and when oil reaches the friction interfaces of a dry clutch the coefficient of friction acting between them REDUCES to approx 1/3 of its dry value thus the amount of torque the clutch will transmit before slip occurs reduces tro approx 1/3 of its dry value and slip is a BIG problem to those who apply torque to the clutch......I.E. They had a VERY SERIOUS clutch slip problem.
Now they could of put in the manuals as they did in Dommy manuals on the problems pages....... TROUBLE . Slipping clutch. POSSIBLE CAUSE. Oil on Plates. CURE. Dismantle clutch plates and wash in petrol. But they didnt put such advice in the Commando books. They did not even want the public to know they had a slip problem. Unfortunately I do not believe they had anyone who knew anything about clutches because had they of done so they would NOT of done what they did......
They asked Laycock Engineering to make the next batch of diaphragm springs 'stronger' to give a greater clamp load to increase the amount of torque the clutch would transmit before slip occured..... Laycock Engineerting manufactured spring 83466 Ref 40 which were approx 0.080 inch thick. This DOD NOT cure the problem so laycock Engineering were asked to do the trick again and produced spring 83466 Ref 50 which was approx 0.082 inch thick. This DID NOT cure the problem so Laycock Engineering produced yet another version of spring 83466 Ref 60 of approx 0.084 inch thickness which in a correctly set up clutch applied a clamp load of approx 550 lbf and still DID NOT cure the slip problem.
Now if you raise the clamp load you also raise the grunt a rider has to apply to the clutch lever to operate it and this is the MAJOR cause of Commando heavy clutch lever action.
Text deleted .....some even suggest that to make clutch lever acrtion lighter you add a thicker pressure plate...Some even flog the things and have done for years AND without knowing and telling customers that if you fit a 0.050 inch thicker pressure plate to a 0.075 inch thick spring clutch you REDUCE not only the release load required to operate the clutch lever by aroumnd 13 % but also the clamp load by approx 13 % making the clutch even more prone to slip problems!! For a later 0.084 inch thick spring it is aprox 18 %. Some of us have the load / deflection curves for these springs and thus know exactly what effect altering the 'stack heoght' has. When I cobble together a dry running belt driven diaphragm sapring clutch for a friends say T140 or T120 I set up the spring to give the clamp load required to suit the differewnt torque capacity requirements giving the friend nice light easy two finger clutch lever operation....it aint hard to do .....
If yoy actually want to learn how Commando diaphragm spring clutches work go try looking at
http://a20b767e.magix.net/.
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