I am in the process of restoring my 1947 40M Manx. I have just assembled the clutch and ensured that it lines up nicely with the engine sprocket. Satisfied, I gave it a spin and was horrified to see that the clutch does not run true, but wobbles laterally by about an 1/8 inch! I have stuck a straight edge across the hub, and checked for run out on the gearbox shaft and all seems ok. However, the backplate, which is bolted to the hub seems to be the culprit.
NOC spares list part A2/381 and they have NOS at a very reasonable £7.50. But on consulting the spares list the 30M / 40M backplate is A11M/381. It would appear that the Manx backplate is thicker!
As I have no intention of racing the bike, would it be possible to fit the standard A2 version? I cannot see how this part, because of the clutch construction, would affect the operation of the clutch, or its assembly.
Obtaining an A11M item would appear to be next to impossible. Is it feasible to have the original trued up by using a press and then lightly skimming? This would reduce the thickness ultimately, so do I go for the A2 version?
Thanks for your help.
Check fit on hub....
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Thanks Michael I have just…
Thanks Michael
I have just stripped everything back down and then put the backplate in my lathe. Putting a dial gauge on it I get a 36 though run out in the middle of the track and 45 though at the edge. So the back plate is definitely not running true. However, it is a lot better than it was. There was a lot of debris came out of the cush drive when I stripped it, although the rubbers were pretty good.
Would I get away with a 45 thou run out? I cannot find a tolerance anywhere in the technical pages, so I assume it should be flat.
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Wonky Wobbling
The later AMC clutches were designed so when the pressure plate lifted, the clutch basket tilted over slightly. This in turn helped separate the plates and prevent drag. Not too sure if that plan worked very well.
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Thats interesting Phil, not…
Thats interesting Phil, not having heard of that ,I did everything possible to eliminate basket wobble including fitting closer tollerance bearings !.Happily the clutch works well and neutral is easy to find. Not having any decent facilities I would probably use a vice and spacers to press the plate into a better shape. Ignorance is bliss in my case.
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I was fooled by plate not seated squarely to hub and appearing to be warped. Check everything independently. In my case what ha happened was one of the new cush rubbers was slightly protruding and not allowing the rear hub plate to seat properly which in turn caused the plate to wobble.