You are totally missing the point. The fact that your Mk3 clutch dies not suffer from slip means that you are not putting enough of the motors available grunt through it to induce it to do so. Even the Norton Owners Club Commando Service notes mention the problem of ‘gunge’ forming on the friction interfaces of bronze plate clutches resulting in drag problems…..’gunge’ that has owners performing the wash the plates in petrol ritual to cure the drag and slip problem and recommended as a cure for clutch slip in my Norton Instruction for models 50-ES2-88-99-Atlas book on the problems page as a cure for a slip problem!! Norton employed a DRY clutch within the oil bath chain case (OBCC) in 1934 when they finally introduced it and it never changed. That’s why the oil level plug set the oil level so it only just touched the chain at its lowest point and shoved an ‘oil excluding band ‘around the basket. Other manufacturers did exactly the same.
A motor cycle multi plate friction clutch correctly designed, will possess, if set up correctly, the quality that it will NOT slip when fully engaged. Does your car clutch slip going up a steep hill with the throttle to the floor when loaded to the gunnels with the family and a caravan stuck on the rear as you use every last dollop of torque the motor can produce? Of course it doesn’t and if it does you know you have a clutch problem.
The ‘gunge’ the Service manual
talks about in the bronze plated clutches is burnt oil, the result of clutch slip generating, very quickly, vast amounts of heat within the clutch which burns off the oil causing the slip in the first place. Several ex Norton/NVT gents have told me it was a very last attempt by Norton to cure the problem of clutch slip die to oil. This being the result of Norton employing a dry clutch within the oil bath chain case in 1934 and continuing to do so to the very end.
The Service book also talks of the early Commando clutch problem which was that the postage stamp sized lumps of Ferodo MS6 friction material would come adrift from the steel backing plate and jam up the clutch causing serious drag problems The problem being caused by the slip due to oil entering the DRY clutch which resulted in the heat which damaged the adhesive bond. To cure that problem they changed to employing solid asbestos containing fibre Don International Don 112 material friction plate. The new ones still in my stock being marked 061339. The Service manual
states that these became impregnated with oil and suffered from glazing, the glazing of course being the result of the heat due to slip which was due to oil entering the DRY clutch…….
You want a wet clutch for your MK3? OK lets PLAY, very simply, at clutch designer.
Max motor grunt 55 ft lb. Primary ratio 26-57. Max torque at clutch 105 ft lb (NOT allowing for losses in chain) Apply rule of thumb clutch safety/service factor of x2. giving a REQUIRED clutch torque capacity of 210ft lb
There are 10 friction interfaces with an effective radius of approx 0.21 ft. The rule of thumb Coefficient of friction values for sintered bronze are DRY 0.34. WET 0.06-0.08.
The ORIGINAL 750 Commando diaphragm spring applied approx 380 lbf clamp load and gave EASY worst case two finger back to the bar freeing off operation YOU will have the 4the edition of the diaphragm spring fitted to Commandos in an attempt to cure the slip problem, each new edition giving an approx 10% increase in the clamp load and grunt required to operate the clutch lever over the last edition!! Your spring applies approx 550 lbf and requires a ridiculous amount of grunt to operate the clutch lever. IN FACT initially it is GREATER than that required for a poxy T140 clutch and owners often fit hydraulic clutch operation to them! Thus the in theory clutch torque capacity will be……………
1. Using early 750 spring DRY………..10 x 0.21 x 0.3 x 380 = 239.4 ft lb
2. ………………………. WET……….10 x 0,21 x 0.08 x 380 = 64 ft lb
3. Using the 550 lbf spring DRY …… ..10 x 0.21 x 0.3 x 550 = 346 ft lb
4. ………………………….WET………..10 x 0.21 x 0.08 x 550 = 92.4 ft l
Now for your correctly designed wet clutch and the RAMIFICATION ……!!!!!
1 Lets increase the number of friction interfaces/plates
WET. Early spring Number of interfaces x 0.21 x 0.08 x 380 =240 ft lb.
Number of friction interfaces = 37.5 , 38 to nearest.
Number of clutch plates required =19.
So explain to me how the hell you will get the lift required from a diaphragm spring to give the lift required per interface if the clutch is to free off correctly. It would also require a MAJOR redesign of the lift mechanism and I dread to think what the static weight would be let alone the rotating weight and a motor cycle multi plate clutch is supposed to posses the LIGHTEST rotating weight reasonably possible not the **** heaviest.
WET. Late spring. It works out to 13 friction plates. The same ramifications apply
2………Lets simply increase the clamp load, Just for a laugh…..
WET. 10 x 0.21 x 0.08 x clamp load = 240 ft lb.
Clamp load = 1429 lbf
So explain to me how you are going to free off the clutch without some SERIOUS hydraulics!!
3……… Lets increase the effective radius of the friction interfaces for another laugh.
WET. Early spring 10 x effective radius x 0.08 x 380 =240 ft lb
Effective radius = 0.789 ft or approx 9.5 inches giving an effective radius of 19 inches which would probably result in a 24 inch in diameter clutch. Ye gods imaging the flywheel effect of that rotating at around half engine speed!! Where would you run the chain? Not around that!! Hell at tick over speed it would probably fail big time taking your leg off after coming through the freshly polished OBCC!!!!
4 ………A combination /compromise.
WET. 20 x 0.3 x 0.08 x 500 =240 ft lb
Sorry but with 20 interfaces you still need to find a lot more lift requiring a major redesign. The rotating weight has been GREATLY increased with double the number of friction and steel interpolates and the lump will have an effective diameter of 7.2 inches giving an OD to the lump of probably 12 inches and running at half engine rpm you could not run the chain around the outside of it….not without it failing big time very quickly.
I now invite you to guess why the Staff of The Motor Cycle in their book ‘Speed and How to Obtain it’ refer to the idea of shoving a clutch within an OBC C as ‘Frankly a Compromise’ and the Ariel system of running the chain within the OBCC with lots of nice thin lubricating oil to keep chain efficiency as high as possible but with the clutch running dry EXTERNALLY beneath a cover as ’A much better idea’. Something Mr Williams did on the Works Commando race bikes ……..
As you will of probably noticed the in theory wet clutch torque capacity of Commando clutches is much lower than required if the clutch is not to slip when fully engaged ASSUMING the rider shoves enough of the torque available from the engine into the clutch. Of course with young Norton owners playing at being racers for decades and on a regular basis performing the ancient ritual of washing the plates in petrol most probably consider clutch slip to be perfectly normal as I once did the heavy clutch lever action of my Norton clutches due to using stronger springs in an effort to cure the slip problem that would test the valve gear to well over 7000 rpm . When I first pulled the clutch lever of the brand new early 750 Commando a friend had speared with in The Island I damn nigh screamed at him’ OK so who is the clever ******* who has disconnected the ******* clutch’ to which he replied ‘Funny but most people ask that question’ Even British road tests commented on it. It was a damn quick learning curve as to how a clutch lever should be operated. Later I read Mr Irvings listings of the qualities a motor cycle clutch should possess and again in the American book first published in 1914 ‘Early Motor- Cycles. Construction -Operation-Service.
IF you take a Commando clutch with the spring correctly set up with the clutch fully engaged and then fir a 0.050 inch thicker pressure plate to it you REDUCE both the load required to operate the lever AND the clamp load the spring is applying to the friction interfaces AND THUS the amount of torque the clutch when fully engaged will carry before, in theory, slip occurs by…………for the original 750 spring approx 25%, for the last 820 spring by approx 23% and for the NON Laycock Engineering spring now available for Commandos from Norton (Which gives a clamp load of approx 440lbf when correctly set up) it reduces by approx 18%.
To my way of thinking anyone running a Commando clutch within the OBCC with oil who already has a clutch somewhat prone to slip would be very silly to reduce clutch torque capacity further….. UNLESS they know EXACTLY what they are doing and I haven’t noticed anyone recommending one does just that tell anyone about the reduction in torque capacity…….
Thus I am informing anyone who bothers to read this so that IF they are considering following the advice of exspurts they are fully aware of some of the RAMIFICATIONS (There are others)
Years ago I phoned RGM asking what effect on clutch torque capacity fitting their 0.050 thicker pressure plate would have just to find out if they knew. They didn’t. They told me they didn’t think it did. Yet another reason I don’t use them.
Talking to the retired Laycock Engineering Chief Clutch Designer and Engineering Director this afternoon asking why when he designed the earlier Villiers Starmaker WET diaphragm spring clutches and employed sintered bronze as the friction material he replied something to the effect that it was the same reason Boeing used the same grade of sintered bronze to stop their planes from running out of runway…..it would take all the abuse any competition rider could ever subject it to and thrive on it UNLIKE the other friction materials available at that time.
AND for ANYONE telling tales of friction materials with as high a C of F value with oil as when dry will you PLEASE inform me INSTANTLY as to exactly what it is with a complete spec and INSTANTLY go on holiday so I can patent it and become one of if not the richest person in the World….as a Ferodo gent said to me at Chapel-en-le-Frith as he was giving me a little lecture on friction materials when I asked if he knew what the new grey coloured material a Ducati dealer told me about which did have the same C of F values wet and dry……Bull**** baffles brains….. the Gent gave me a funny sort of look and I said ‘I am talking bollocks aren’t I ‘to which he replied ‘Well let me put it to you this way, if ever you develop such a friction material will you please do two things….……….’