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An AMC Clutch Question

Submitted by john_ward1 on Mon, 20/03/2023
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Heavy Twins

I have what I believe is referred to as an "early" type AMC clutch where the chainwheel/basket has friction inserts and the hub back plate is plain. I also have 3 friction plates with external tangs and 4 plain plates with internal tangs. However, when the clutch is assembled, it looks like there is room for at least another pair of plates. How many loose friction and plain plates should there be in this sort of clutch?

 

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Submitted by robert_tuck on Tue, 21/03/2023

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Early clutch had 4 plain and 4 friction with an extra plate friction one side that the pressure plate bears on. So you are missing 1 friction plus the special plain one side friction the other side.

Ok... I'm not sure I understand. Sorry if I'm coming over as being a bit thick.

My chainwheel, basket has friction inserts so the first plate in has to be a plain one followed by a friction plate. If I add 3 more plain and 3 more friction, to give 4 of each as you indicate,  I end up with a friction plate on the outside. The aluminium pressure plate, with the springs in, can't bear up against a friction plate, so I would need to put in another plain plate, making a stack of 5 plain plates and 4 friction plates. Why would the final plain plate need friction material on one side? The friction side of that plate would either go against the final friction plate or the aluminium pressure plate, neither of which seems sensible to me.

Submitted by paul_standeven on Tue, 21/03/2023

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four friction plates and five plain. The outer one which meets the pressure plate is a plain one. This early AMC clutch is very similar to a Norton one, but with a different pressure plate and spring bolt arrangement.

Interesting, the friction blocks in the chainring alternate.  All the Norton clutch chainrings I have seen have the friction blocks wide side out, narrow side inwards.

Paul

Thanks for the confirmation. The plain plates that I have are rusty and pitted so I'll order 5 new plain plates as well as the four new friction plates. I've replaced the cush rubbers in the clutch hub... that took some serious squeezing to get the 3 small rubbers in. With the new plates, springs and spring retaining nuts, that will be the clutch sorted, I hope.

As far as the alternating friction inserts are concerned, I have no answer. The clutch assembly was in one of the boxes of bits, that I purchased with a 650SS basket case project. AMC gearboxes and clutches were used on many different models of different marques. There is no guarantee that the item I have originally came from a Norton, much less a 650SS.

If anyone is remotely interested, the on-going rebuild / restoration story can be found HERE

Submitted by robert_tuck on Tue, 21/03/2023

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I still think it goes,  backplate /hub,basket (with inserts), plain,friction,plain,friction plain,friction plain, plus final friction/plain combination plate with plain side against alloy pressure plate. Total 8 plates ( 3 types)   But I could be wrong!! It has been known.

Submitted by ian_macdougall on Tue, 21/03/2023

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You will probably find that the new plates currently available will be slightly thicker than the originals. If so the basket will accommodate one less of both types.

Submitted by robert_tuck on Tue, 21/03/2023

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After some research it would appear that the  last plate is not a combination of friction and plain. but just a plain plate.  So that seems to point to seven or nine plates in total  for this clutch which could be a Norton  rather than AMC? 

Submitted by david_cooper on Tue, 21/03/2023

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Norton clutch friction plates have tangs on the outside, which is what you say you have.  AMC friction plates have tangs inside.

Owners might have added or removed plates to suit.  Manx bikes had only 3 friction plates to save weight.  But they didn't have the oil bath.

Submitted by howard_robinson on Wed, 22/03/2023

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It sounds like it's an early Norton clutch.  Another gotcha is the size of the splines on the clutch hub.  I have some plain plates that are too wide to fit the hub.  The outer tags on the friction plates are usually all the same width. Be careful with your right hand - the 650SS usually had an eleven pate clutch and there was a good reason for this.   Good luck, Howard   

Submitted by paul_standeven on Wed, 22/03/2023

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and reassembling the clutch.  The rust will clean up.  Use high temperature grease on the rollers, sparingly. 

The early AMC box came with an interim clutch.  It got the alloy pressure plate and revised spring bolt and nut arrangement, but the plates are the same way round as Norton ones - friction inserts in the chain-ring and the outer plates.  Tags-in are plain plates.  Those parts are the same as Norton clutch parts.  About 1960 came the reverse clutch. with friction material bonded to the backing plate, and on the inner plates.  Outers became plain, like the chainring.  This bike has the early AMC clutch, along with the AMC 1 gearbox.

 


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