C: Clutch Twin clutch . centralizing plunger.

Gary Gittleson

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I have reassembled the clutch with a new drum and friction plate. I checked the plunger springs and all seems to be well in that area. Attached are three photos of the old drum showing the wear in the slots, the thin-walled carrier (for Timetraveller's benefit) and finally, the odd asymmetry of the inner plain clutch plate (C21) that I recently discovered. The tabs on the old friction plate were also well worn.

In addition to the wear in the drum slots and the tabs on the friction plate, I noticed that one of the clutch springs was hanging up in its cup (C30). It had a burr and some roughness. To cure that, I sanded the inside of the cup with a little Dremel sanding drum. It seems OK now. Then I had to work on the tabs on the new friction plate. They were all about .006" wider than the slots in the new drum. I mounted the plate in soft plastic jaws of a vise and filed one at a time, counting strokes of the file on each tab, measuring, filing etc. working both sides of each tab, little by little. You get the idea I'm sure. The plate is now a nice snug fit without binding and no noticeable backlash.

Now the problem with the inner plain plate. The 9 holes for the pins are not properly centered in the plate which sets the plate off by maybe 1/16", as can be seen in the photo. It almost touches the drum on one side in the 4 O'clock position in the photo. It appears to be touching in the photo but there is some clearance. I'm guessing it isn't critical but I'd appreciate any thoughts on the subject. The plate is flat.

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I can't report the results on the road yet. We're buried in snow at the moment and a lot more is on the way. Spring can't come soon enough.
 

Bill Thomas

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Gary, I think that plate will give you trouble, Can you compare it with an old one ?.
I think there is always some movement on the drum, So I think they will touch ?.
Cheers Bill.
 

Gary Gittleson

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That plate is not new. It's quite old, in fact; maybe even original. True, there's some small movement of the drum but at least by hand, I'm not able to make them touch. Later today, I'll examine the drum to see if there's a witness track on the old drum. If so, it's time for a new plate. If not, I guess it's OK. ?
 

timetraveller

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I agree with Bill. The offset of that plate looks like it will cause trouble. Regarding my mod for the rear of the shoe carrier shaft, it looks to me as though there is enough metal there to do something like my mod. Remember that an 'o' ring only needs about a five thou nip to act as a seal and there is no significant pressure trying to cause a leak at that point. It looks to me as though an 'o' ring with a one or two mm section could be made to fit in the rear of that shoe carrier. My crude attempt with a valve seat grinder might be too crude but a good machinist with either a four jaw chuck in a lathe or a mill with a rotary table could easily make a recess to fit whatever 'o' ring you can find.
 

Gary Gittleson

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Does the drum spin true, Something looks wrong to me.
Yes, the drum spins true. It's quite obvious what's wrong. It's plain as day that the nine holes are drilled on a circle which is not concentric with the plate. Look carefully at the distance from the pins and the inner large hole. Compare for example, the pin at three O'clock to the one at nine O'clock or even worse at eleven and twelve. With the plate off and on the bench it's quite clear that the plate itself is the culprit.

I checked the old drum and there's no groove where the plate was rubbing. It is somewhat polished in that area.

So I suppose it could be causing some slight drag and a small amount of unwanted engagement. So here's my question. Does it matter that the plate is offset, besides the possibility of touching the drum? If not, I could just grind a bit of the plate to give it more clearance. Or I could just replace the plate.

With regards to the Timetraveller O-ring mod, I'll give it a go first with two O-rings on the outer end of the carrier. When I opened it up, the O-ring that was there was in very poor shape. It was probably not seated properly before and got crunched by the nut.
 

Chris Launders

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If you don't want to fit a new plate I would just take some off the outside where it's close to the drum, just make the outside concentric with the drum, just run a marker pen round inside the drum and it will show you where.
 

Peter Holmes

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The clutch shoe carrier looks like the inner face has fretted away, it should be an even machined surface, not uneven and worn as the photo shows, although it has been a subject for discussion on this forum, this normally happens when when the C20 has been run loose for a protracted period of time, I like to do this nut up FT, and always go to the next spring slot as opposed to backing the nut off to the previous slot, but I do know of others that have said this is not important.
 

Hugo Myatt

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If you don't want to fit a new plate I would just take some off the outside where it's close to the drum, just make the outside concentric with the drum, just run a marker pen round inside the drum and it will show you where.
I had exactly the same problem with the clutch plate when I acquired my Rapide more than 50 years ago. I have every reason to suppose it was an original plate. At the time the only spares available were from Harpers and the quality was not of the best. I doubt that in my then impecunious state I would have been able to afford a Harpers replacement anyway. I had to live with it for some years. It had some intermittent foibles. It would occasionally drag and sometimes it would not re-engage after lifting the clutch. I would have to remove the clutch dome and give it a kick - in neutral of course. I never managed to cure it until I replaced the plate with a concentric one.
Hugo
 

Gary Gittleson

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The clutch shoe carrier looks like the inner face has fretted away, it should be an even machined surface, not uneven and worn as the photo shows,
I see what you mean but don't know what problem that would cause. I do tighten the nut down and go to the next tighter notch as you mention. But I never changed the carrier and never noticed this "problem". I believe the bike had two previous owners, so I've got others to blame. :)

It would occasionally drag and sometimes it would not re-engage
I never had engagement problems. I'm going to shave the plate down and try it once weather permits.
 
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