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C: Clutch Clutch plunger spring adjustment

Bobv07662

Well Known and Active Website User
VOC Member
The clutch on my 50 Rapide is a bit grabby. I've had a quick look behind the cover and the good news is that it's dry inside. The bad news is the C11 plungers are not touching the pins. They are about 1/16 from contact. I've read where the adjusting screw C12 can be accessed by drilling a hole in the linings. My question is can I drill that hole large enough to remove C12 in order to check or replace the plunger springs without affecting the service life of the linings?
 

Bill Thomas

Well Known and Active Website User
VOC Member
Bob, As long as the springs are still springy, I fitted a pair of cut down C15 tubes,
And slipped them over C14 pins, Where C11/1 touch, Tricky job I think .
 

stu spalding

Well Known and Active Website User
VOC Member
Hi Bob, as long as the plungers aren't hardened (some are), and the gap between plunger and pin is only small it is possible to undercut the collar on the end of the plunger thus dropping the plunger in to take up the slack. I recently did a clutch where the pivot bores had been "reclaimed" by stuffing a 5/8" drill through the hole where it stood and bushing. This is all wrong as it locates the plungers away from where they should be, the only way to reclaim pivot bores is by jig drilling. There are a couple of articles in MPH 820 & 821 which may be of help. Cheers, Stu.
 

BigEd

Well Known and Active Website User
VOC Member
VOC Forum Moderator
I don't think that a bit of clearance at the end of the plungers is a problem. There is a counterbore in the hole for the plunger that limits how far it sticks out.
If your clutch is grabby the first thing I would do is to make a hole to get access to the adjusting screw for the plunger and increase the tension on just the C7 shoe. Too much pressure and the clutch will slip, to little and it will grab. Use small increments maybe 1/4 - 1/2 a turn at a time. In your case try taking a little off. You will soon see if that is an improvement. It is a bit of a pain removing and refitting the shoes after adjustment. Leave the clutch cover off for a quick test ride, keep your trousers away from the clutch.
It is quite complicated compared to a multi-plate clutch and difficult to understand how it works when you first look at it. (Or even the 2nd, 3rd, 4th ... time. ;)) Mine has quite a lot of "slop" in it, I really should replace some of the worn bits. It does, however, work well and has a very light action at the clutch lever. I removed a multi-plate clutch to fit the original once I'd got a bit of an idea about the adjustments.
Clutch shoe assembly2_cropped.jpg
 

stu spalding

Well Known and Active Website User
VOC Member
In order for accurate adjustment of the clutch to be obtained, what is required is a dummy centre (pictured). It's a simple turning job in hard plastic. This removes all guesswork from setting the thimble C12 to the right depth. Simply assemble the clutch on the centre and adjust C12 until the shoes expand to six inches when actuated. It is essential that the travel of the plunger in C7 is absolutely smooth as the slightest resistance will result in a grabby clutch. People have been saying for 70 years "Oh, it wouldn't be a little thing like that" but it is. I spent a great deal of time and effort in 2014 sorting out exactly what makes the twin clutch tick and when it's right it is light, progressive and smooth in operation, when it's nearly right it's a piece of junk. Cheers, Stu.P1050864.JPG
 

vibrac

Well Known and Active Website User
VOC Member
I think Stu has got that absolutely right. I have finally decided that the original clutch is the thing for the road (And bear in mind my first major job on a Vincent was to fit a Norton clutch to my first twin from a article in a mag when I was still at my first job 196*) - not that I have an original clutch fitted on my twin because I dont have a road one anymore its a racer and a belt drive with a newby clutch that is either in or out is just the job on the track.
 

Bobv07662

Well Known and Active Website User
VOC Member
In order for accurate adjustment of the clutch to be obtained, what is required is a dummy centre (pictured). It's a simple turning job in hard plastic. This removes all guesswork from setting the thimble C12 to the right depth. Simply assemble the clutch on the centre and adjust C12 until the shoes expand to six inches when actuated. It is essential that the travel of the plunger in C7 is absolutely smooth as the slightest resistance will result in a grabby clutch. People have been saying for 70 years "Oh, it wouldn't be a little thing like that" but it is. I spent a great deal of time and effort in 2014 sorting out exactly what makes the twin clutch tick and when it's right it is light, progressive and smooth in operation, when it's nearly right it's a piece of junk. Cheers, Stu.View attachment 36917
Stu, Turning that dummy center is something easy for me. What I'm missing is the "assemble the clutch on the center"...Do I remove the shoe/carrier assembly and then place the dummy center inside that shoe/carrier, then adjust the C12s to get the expanded shoes to measure 6"?
Also, how do I make sure both shoes are expanding equally? Just measure to the center of the dummy center tool?
Thank you for your insight into these clutches. I do see how the clutch operates, it is the seeing how to make it operate properly that I now find myself tackling! I have quite a bit of experience on automotive single and multiplate clutches and have never seen a clutch as elegant as these in a Vincent. It is what makes these bikes unique.
 

stu spalding

Well Known and Active Website User
VOC Member
Hi Bob, the dummy centre should be a snug fit in the shoe carrier C3 and a slip fit in the plate carrier C13. Assemble the carriers, shoes, links etc and hold C3 in a vice, keeping in mind that the bearing surface for the chainwheel bushes is not hardened and is easily marked, put a large screwdriver through the pins C14 and turn C13 in either direction against the plunger spring, I assume you've thrown away the double springs and fitted the single spring as it was found that the double springs binding during compression was a cause of clutch grab. The single springs are available from Derek Sayer although I should imagine that other people have made them by now. Turning C13 will expand the shoes to the point where the plunger hits thimble C12 and the linings should be 6 inches across at this point. I reline the shoes with oversize linings and jig grind them on the lathe to make sure that they're concentric. I hope this is of some use but please feel free to ask if you need more info. Cheers, Stu.
 

Bobv07662

Well Known and Active Website User
VOC Member
Just an update...the clutch has improved after some repair. The clearance between the C11 plungers and C14 pins was .055" so I turned up 2 bushings and installed them over the pins. I adjusted the plunger settings according to Stu's suggestions above and then reassembled the works. That reassembly was slightly complicated by a previous owner updating to the series D C3 carrier and C20 nut but they did not install the small threaded adapter to convert my C transmission shaft to the shouldered D spec. A call to John Healy at Coventry Spares had all the required parts on my doorstep in short order.
The clutch now has a very usable "friction zone" where nearly none existed before. Hopefully it remains dry and I am grateful for all who offered advice and assistance here at the VOC!
 

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