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Plastic clutch rubbers?

Submitted by richard_salt on Tue, 21/05/2024
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Nortons - General

I recently bought a set of clutch rubbers for my Dominator.
I had  taken the primary drive cover off to see why the chain was slackening and tightening excessively. The shaft is not bent, but I found that the clutch basket was not positioned centrally on the spider, it was off center in the small clearance between the spider arms and basket (giving about 20 mm up and down movement in the chain). The rubbers had deteriorated such that the spider could move sideways in the basket.
The new “rubbers” – bought from a known supplier – are totally wrong. The attached sketch shows the differences from the original. In addition, they are extremely hard, can hardly be compressed at all. They resemble plastic more than rubber.
The larger is 3mm wider than it should be, so if fitted, the smaller would have to be 3 mm thinner. It isn’t so I have tried to cut off the 3 mm while leaving the shape as it should be. The material cannot be cut, it has to be sliced with a very sharp knife.
Not being in the UK, I cannot just send them back to the supplier. Anyway, If I did, I would probably get the same thing in return.
Can anybody shed some light on my problem? Has anyone had a similar experience?
 

Attachments
Clutch rubbers.jpg

Submitted by john_doig on Tue, 21/05/2024

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Sounds like the spider and possibly the front and rear covers are worn out - replacing the rubbers won't help.
John Doig
 

Submitted by richard_salt on Tue, 21/05/2024

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The chain tension/looseness up and down varies from about 3 mm to 20 mm as the engine is slowly rotated.
This results from the clutch basket being up to 20 thou off center. 
The only circumferential movement which could cause wear between the spider and the basket plates is that which results from the compression of the rubbers. Negligible.
 

Submitted by jan_nelder on Tue, 21/05/2024

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have you dissembled the whole clutch to check where the looseness comes from? 
 I don't think it relies on rubbers for basket concentricity with main shaft.

Submitted by richard_salt on Tue, 21/05/2024

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You are all correct, the spider cannot move sideways in the basket, it is firmly located by the two end plates. I wasn't thinking clearly.
I have found that the splined spider probably wasn't sitting true on the shaft.
I now have a new spider and new end plates.
However, my problem with the rubbers remains.
They are too hard and too large.
Does anyone have any experience of this?
Thank you all.

Submitted by david_cooper on Tue, 21/05/2024

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Metric dimensions are confusing here!  Dimension 'a' in the metal is one inch (25.4mm).  The rubbers are approximately 7/8" when new.  That allows them to expand sideways when they are squeezed.  Eventually they fall apart but before that one of mine expanded sideways to more than 25mm.  I cut the sides down with a craft knife, and re-fitted them because mine were swollen but not rotten, and the new ones I bought were far too stiff to fit, even with the correct tools.

Submitted by dan_field on Tue, 21/05/2024

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Those rubbers are a pain to get in, You really need a spare main shaft in a big vice and a tool made from a clutch plate or two welded to a handle, I put the large ones in first then used the tool with an old stanchion for extra leverage to compress the rubbers sufficiently to get them in - I might have used some silicone grease to help! I remember much grunting and swearing! While you are there make sure that the spring studs are properly tight and locked at the back of the clutch, I've found 2 clutches with lose studs recently. 

I should at that my clutch had 3 large rubbers and 3 small. 

Clutch

Dan 

 



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