C: Clutch Clutch plunger spring adjustment

vibrac

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VOC Member
Imagine all those years ago when folk gave up on clutch and gearbox issues............Out with a bloody big hack saw........... The horror of watching someone do it ..........The shame, the shame......... o_O
Gissa chance mister strewtf I wus only nineteen.... :confused:
 

stu spalding

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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.
 

Bill Thomas

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VOC Member
Clutch-cpM002diagram.jpg
 

Bobv07662

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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!
 

Alyson

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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, my man, what would it take to turn a few of these up for folks like me that don't own a lathe ? I'd be happy to pay you even !
 

Alyson

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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
actually an old G3 should also do the trick ?
 

stu spalding

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VOC Member
Stu, my man, what would it take to turn a few of these up for folks like me that don't own a lathe
Hi Alyson, thanks for your interest in this, unfortunately my disabilities mean that I struggle with my own work, far less doing "outsiders". I did mention to Ian Savage that it might be a worthwhile project for the VOC Spares Co to get involved in. Every twin owner running a standard clutch should have a dummy centre as it takes all the guesswork out of setting up the C12 thimbles. Cheers, Stu
 
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