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Primary case sealing rubber

Can anyone tell me the dimensions of the rubber sealing strap which goes around the inner chaincase, and whether the rubber is relatively hard or soft?

I've had mine off for quite a while, and now that I try to fit the outer case, it won't go on, the rubber seal is too thick and too hard. Its measured dimensions are 25mm wide and 10mm thick. It is very hard, I can hardly compress it at all with my fingers, so it won't compress to accept the outer case.
It also has no taper front to back.

It came off the bike ok, so I don't understand why now it is too thick and too hard to do its job.

Has anyone tried using another type/size of rubber, maybe softer so it fills dents more effectively?

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25mm x 10mm is about right for the sealing strip although modern square edged replacements seem much harder than originals and lack the rounded taper shape.  If yours came off however, it should go back on again. I find the application of rubber grease and a ratchet strap can make things easier. The band needs to be a snug fit on the flange, taking a thin slice out of it and regluing with cyano can help.

These days I prefer to use black neoprene foam strip which comes in a variety of sizes and lengths and is much cheaper. Joined and fitted as above, a slightly stretch fit over the flange. A thin film of oil on the self adhesive side prior to application helps to prevent sticking to the flange, otherwise a pig to remove. The softer foam moulds itself into the shape of the outer case.

Hope this helps.

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My rubber seal is certainly not the original type, it is so hard that the outer case has no chance of compressing it to fit the valleys and hills on the inner. 
Why it doesn't fit now I don't know.
As we don't have a supplier of new parts for these old bikes where I live, everything new has to be imported, and sent by courier. With courier costs, taxes, import duty, local delivery costs and VAT, costs of even small items becomes a problem. In addition, when you want to finish something, having to put it aside for a week or more is annoying.
So I have made a seal of a softer compound, I don't know just what it is. It came from packing used for transporting vehicle windscreens and is in lengths long enough. I soaked a piece for a week in oil, it didn't decompose or expand.

It's fitted now, and I've put oil in the case. We'll see in the morning if all is ok.

 

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There are two at least two types.  Dommie has a rectangle with a ridge along one corner, and some (all?) Singles have a wedge shaped one.  Usual suppliers have them.

 



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