650 twin AMC gearbox/clutch issues?

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mjf65
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650 twin AMC gearbox/clutch issues?

Post by mjf65 »

I think the clutch lever pressure has been gradually increasing over the last few month with more effort required to engage the clutch, this became more evident when having a ride on a friends 650 Thunderbird with a light clutch action but a very vibey motor but that's another story.

Anyway, a couple of weekends ago my clutch cable actually gave up the ghost and snapped at the gearbox end. After fitting a new one I went out for a test ride. The clutch felt heavier than ever with maximum effort required on the leaver, it was unbearable to ride. The cable routing is fine and when disconnected at the gearbox end the inner cable moves very easily. Where and at what potential issues should I be looking at first? I intend to take the gearbox cover plate off so I can see if I can recover the old cable nipple.

I have to say there has been no clutch or gearbox issues in over a 1000 miles since March and the clutch still doesn't show signs of drag or slip, it just takes massive effort to engage it.

Regards

Mike
Groily
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Re: 650 twin AMC gearbox/clutch issues?

Post by Groily »

Do you think the alignment of the arm at the gearbox end that the cable hooks onto could be 'off'? If the cable is smooth, the pushrod is free and the clutch set up within reasonable limits, with a cluster of ungummed unjammed plates, could just be? It needs to slide nicely in its notch / guide, but they can be really hard if the angle's wrong. There's a tool for alignment in fact, but 'by eye' works often enough.
Have to say, of my 3 AMC 'boxes /clutches, only one clutch is light as I'd really like, and none compares with the Burman on another bike. The heaviest is a near-new diaphragm job on a belt-primary Notrun, which is annoying. But with 7/8th centres at the 'bars, a gentle route for the cable, and clutch springs not over-tightened, it should be at least so-so I reckon and my Mod 31 is a 2-finger job now, although it hasn't always been!
Magnet on a flexy thing to try to get the broken bit out maybe? Not much room in there, I know, but might just do it and save a messy job?
dodger
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Re: 650 twin AMC gearbox/clutch issues?

Post by dodger »

This happened to one of our group on a battle field tour in France (Hughie Upward), turned out the clutch hub nut had come undone.
JEAN-NOEL
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Re: 650 twin AMC gearbox/clutch issues?

Post by JEAN-NOEL »

I agree with Dodger : I have experienced this problem in 65 & 66 when I had a M30. No problem with the G12CSR as the clutch hub nut has been fitted with blue Loctite...
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clive
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Re: 650 twin AMC gearbox/clutch issues?

Post by clive »

Came back from a ride on my G11CS and the clutch started playing up badly a couple of miles from home. Would pull in with difficulty but would not then release. At my garage I was about to start disassembling everything but fortunately thought of checking the bolt that the lever pivots on. Sure enough this had gradually tightened up with use. Ease it back and suddenly the action is easier and the clutch release when the lever is released. Worth a check before you start pulling everything else down.
clive
if it ain't broke don't fix
56G80S
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Re: 650 twin AMC gearbox/clutch issues?

Post by 56G80S »

Groilly's comment about alignment of the lever arm carefully with the hole in the outer case for the cable strikes a bell. Several years ago, when re-assembling my AMC box, I took extra care with this and the clutch was lighter than it had been before disassembly - although I don't see how it would change if all tight in the first place!

Clive's point very good to0, Memory may play me false but I thought there was an early form of self locking nut on the pivot bolt? Haven't checked by parts list though.

Johnny B
Mick D
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Re: 650 twin AMC gearbox/clutch issues?

Post by Mick D »

56G80S wrote: Thu Jul 22, 2021 10:24 am I thought there was an early form of self locking nut on the pivot bolt
Correct Johnny, often referred to as an aerotight nut:
Aerotight Nut.png
Regards Mick
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mjf65
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Re: 650 twin AMC gearbox/clutch issues?

Post by mjf65 »

Well after removing the gearbox cover plate and retrieving the broken end of the nipple the lever arm, ball bearing and pushrod movement all checked out fine. Next I removed the primary chain case cover, the clutch hub nut is tight and the clutch plates were all moving nice freely, I removed them and cleaned the friction plates and dressed the tangs on the steel plates. There is a bit of end float on the output shaft The clutch action is still really tight, I think it must be the new cable once the clutch is engaged. Back to the drawing board tomorrow morning.
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