CP clutch upgrade

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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CP clutch upgrade

Postby Gordonian » Fri Oct 12, 2018 8:30 am

Hi All,

I've been having trouble with the CP clutch on my '47 M18 where one of the friction plates rotates within the basket and locks the clutch. My question is, has anyone ever updated to using the outer basket from the B52 clutch. It has the same 40T sprocket, and diameter is the same. If it uses the same size and number of rollers then the center bearing must be the same. Obviously I would have to buy the B52 friction plates. Anyone ever done this.

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Re: CP clutch upgrade

Postby Andy51 » Fri Oct 12, 2018 8:05 pm

Hi Gordon, it can be done. Many years ago I had a '54 G80 (my 1st), bought for £75 from a man in a pub - as we did in those days! It was a runner, and came with some spares, including a B52 'box. It wasn't till a few years and many miles later I took it apart to paint it that I discovered it had a CP 'box and, I am reasonably sure, a B52 clutch. I put it back together with the B52 'box only to discover the mainshaft was bent - hence the PO had fitted the CP. A NOS B52 mainshaft (£8.00 from the spares scheme - things were cheaper in the '70s!) and back on the road I went, using it to get to work. The B52 clutch came off the CP mainshaft just as easily as the B52 one went back on, so they would appear to be fully interchangeable - same clutch fitted on both mainshafts. Andy

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Re: CP clutch upgrade

Postby clive » Fri Oct 12, 2018 8:43 pm

The clutches are interchangeable. Personally I prefer the CP clutch with its outy ears on the friction plates. Its easy to file the clutch basket back when everything is worn. The B52 box has internal slides for the friction plates and once they are worn its a pig to file them back resulting in a clutch that drags. I am struggling to understand how a friction plate might rotate within the basket. The ears ought to stop this happening unless you have too many plates for the size of your clutch centre. These were different for the 350 and 500, the former needing 4 plates the latter 5 plates. Have you got new clutch friction plates. My experience is that they are thicker than original ones and can result in the last plate falling out when the clutch is activated, it then jams when released. Solution for me has been to use a combination of new and old plates. If you cannot do this try reducing the number of plates, its unlikely to slip unless you are thrashing it on takeoff.
clive
if it ain't broke don't fix

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Re: CP clutch upgrade

Postby Gordonian » Sat Oct 13, 2018 12:38 pm

Thanks for your reply’s. The clutch plates have only done about 1200miles and came from a reputable supplier but to be fair, the ears could have done with being a bit longer as they are only flush with the edge of the basket. Last time I stripped it, it was the fourth plate that had slipped round between the leaves of the basket. I bent the leaves in a bit and put it back together. This lasted a couple of runs before doing it again. I haven’t been able to find new CP baskets for sale anywhere. I shall sort it out over the winter one way or the other. Thanks again

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Re: CP clutch upgrade

Postby 56G80S » Sun Oct 14, 2018 8:35 am

Just for extra reassurance, I was apparently also using a CP clutch with a GB box. Currently swapped that out to put the AMC box and clutch in as I found the GB required a much more "relaxed" gearchanging style rather than supporting a full chat approach.

I had a problem with the the start of cracking on the basket itself inevitably at the right angle where the leaves sit onto their base. This required some very early welding and filing before it became too damaged. Might be worth taking a close look at the "root" area of the basket leaves.

Johnny B

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