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C: Clutch Twin clutch . centralizing plunger.

john998

Well Known and Active Website User
VOC Member
In a drawing of the twin clutch posted on this forum it appears that the centralizing plungers C11/1 are shown in contact with the both C14 pins. Is this correct?
In my experience there is always some clearance that allows C13 a few degrees of rotation either way before any contact.
John Stainton.
 

Gary Gittleson

Well Known and Active Website User
VOC Member
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.

20210127_181821.jpg20210124_190523.jpg20210205_193452.jpg

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

Well Known and Active Website User
VOC Member
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

Well Known and Active Website User
VOC Member
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

Well Known and Active Website User
VOC Member
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

Well Known and Active Website User
VOC Member
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

Well Known and Active Website User
VOC Member
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

Well Known and Active Website User
VOC Member
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

Well Known and Active Website User
VOC Member
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

Well Known and Active Website User
VOC Member
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.
 

Cyborg

Well Known and Active Website User
VOC Member
Unfortunately the C20 probably has enough runout that you could try rotating the C21 to a different spot and end up with more clearance. Personally I would replace the C21. One because it would drive me nuts knowing it’s off and two it will add some additional shake to the shoe carrier etc. and three... the way governments are printing money, it won’t be long before a C21 is worth more than the family fortune.
 

Gary Gittleson

Well Known and Active Website User
VOC Member
Unfortunately the C20 probably has enough runout that you could try rotating the C21 to a different spot
I don't see any appreciable runout in C20. If there were enough to compensate for the C21 problem, I'd guess I'd have some noticeable symptoms since that would throw C13 off center as well. When the clutch is fully assembled, C23 does not inherit the eccentricity. C21 is really quite far off, very visible when it's off the bike just sitting on the bench. I measured the runout of C21 and the center of the circle of 9 holes is about 1mm off.


I wondered if C13 was a Friday job ?.
I don't think C13 is at fault here. OK. I'm convinced that I should replace C21. I was also worried about vibration caused by the out-of-balance C21. See picture of C21 off the bike below.
20210208_192523.jpg20210208_194316.jpg
 
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Cyborg

Well Known and Active Website User
VOC Member
I was being a little over dramatic? I wouldn’t actually expect there would be enough runout on C20 to compensate for what you have there. Maybe move it away from the drum slightly. Worth checking the C20 though. Agreed C23 wouldn’t inherit the eccentricity at least not directly. Just whatever vibration and any extra runout in the carrier assembly that’s caused by the C21 being out of balance. Maybe not all that much in the grand scheme of things, but worth correcting I think.
When you receive your new C21, have a close look at it. On the back side that sits against the C13 there is a fairly substantial burr that is uneven and jagged. It will not allow the C21 to sit flush and evenly against the C13 and will cause runout on the C21. Some of it also looks like it would break off over time. Not likely the swarf would cause a problem in the clutch housing, but don’t need any extra crap in there.

PS... not sure what they used to carve that hole, but they should probably sharpen it..... also add a note to the drawing suggesting the edge should have a tiny radius?

A20C79F6-40F2-40C9-955C-AECD4A3CB56B.jpeg98D07288-64C0-4C28-80FF-54AA0198A549.jpeg
 
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Gary Gittleson

Well Known and Active Website User
VOC Member
I have enough used parts in my "clutch box" to pretty much build a complete clutch, including 2 C21 in reasonable shape. That's if you haven't got a new one on order yet.
The kind offer is much appreciated.

I have ordered the new C21. Items usually arrive here within one business day from Coventry Spares. By the look of Cyborg's new one, a used one might be better, eh? Well no, if all that's wrong is a rough edge on a hole that doesn't require much precision, it'll be fine in the end.

I'll inspect the new C21 carefully and de-burr it as needed. Maybe it will even stop snowing sometime this year and I'll be able to report on the results.
 

Cyborg

Well Known and Active Website User
VOC Member
Other than the burr, which is a humdinger, it seems fine.

Guess you don’t want to hear about our Crocuses popping out of the ground or the Rhododendrons blooming and goldfish frolicking in the pond? Although it’s a little chilly today.....
 

craig

Well Known and Active Website User
VOC Member
Gary, Where do you purchase the torx drive 406, 2BA csk screws?

MO02-406Ref.jpg
GaryClutch2.jpg

It looked like torx drive, but maybe it is allen drive #406 screws.
 
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Marcus Bowden

VOC Hon. Overseas Representative
VOC Member
Torx may be slightly better than Allan screws but the normal slots will last longer, but using an electric screw driver / torque drill the blade will slip out but a small central hole in screws, with the blade bit ground to locate in hole will make life easier. When complete get duck tape and stick it over the screws, have done this for 50 plus years, saves the machining on the inside of the cover. Part of my emergency kit is a used roll of duck tape (1/4" thick) with the center cardboard removed to the first round of sticky then placed in a vice and flat pack it, much handier to stow in a tool box.
bananaman.
 

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