I had some clutches on the bench yesterday, and was sorting through to have a look at potential wear issues, especially the top hat thrust bearing.
But then I noticed this:
Almost all of the clutches (I had five to choose from) had worn grooves into the spring stems, where the coils of the spring had been in contact with the inside edge.
If the spring settles into the grooves, it won't release smoothly....
This seems to be caused because although the spring fits the column fairly well at the inner end, the actual washer under the bolt which holds the spring in place allows the spring to slip sideways; and because the post is tapered it allows the spring to move out under centrifugal/centripetal force.
When the spring does this, as the clutch is at rest (not pulled in) then the spring is free to slide over it's post.
But as engine speed increases, during clutch slip, during a hard launch, the forces acting on the spring push it outwards against the post, and at the point where the spring is reaching bite point it slips into the grooves with a sudden movement, leading to more engagement- clutch locking up and a graunching noise.
All theory, of course, but one of the clutch centres has almost no wear, and so I've fitted the unworn clutch centre, and will refit the standard MC and slave cylinder to see if it slips. (I had previously converted the clutch to a hybrid hydraulic/cable operation using a Varadero clutch cover).
If it doesn't slip, then I may have found the answer.
A possible solution would be to:
a. file the inner edges of the post smooth- drawback is that you can't repeat this indefinitely, it would weaken the post slightly, mean taking the clutch cover off regularly, and allow even more movement for the spring.
b. find a hard metal section of tube to slide over each post, between the spring and the post. Length would have to be short enough not to compromise full compression.
c. Fit a stepped washer, with a smaller diameter section which fits into the spring to hold it in position relative to the bolt head- disadvantage is that there may not be enough clearance between the washer and tip of the post, if it fouls it would again compromise spring travel
d. fit a dished washer, with an outer lip that captured the top of the spring and held it concentric with the fixing bolt.
D looks to be the best option for a permanent solution.
Anyone else got a spare clutch they can inspect, and let us know if this is a common wear issue?
All comments on the theory welcome, as ever.
It's not falling off, it's an upgrade opportunity.
