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JM 159 clutch case depth ?


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Are you saying the basket is positioned too far to the right or asking if it could be?  As you mentioned before that the chain run from basket to crank sprocket was in line, but if the basket is positioned to the right the chain run would be off if the crank weight is fully located, so not sure now if your saying the basket is to the right or asking if it could be

The extra balls could be there for any reason really as it's impossible to know what someone has done in the past but yes, the basket being offset would offset the whole assembly. There are different length pushrods so that's another possibility, too short a pushrod

I'd have to check on an engine, which I don't have one in bits at the moment, but I think It is only the basket (specifically the basket bearing inner race) that sits against the spacer. The hub pushes into the basket bearing but I don't think the end of the hub goes as far as touching the spacer so if the basket is too far to the right then the hub will be also, bringing the pins closer to the case.

Is the bearing located properly in the basket. There is a circlip that retains the bearing, if that is missing has the bearing moved outwards which would push the basket towards the casing, but then I'm not sure if the hub would bind up when fitted and tightened

Does the top hat definitely sit right up against the gearbox bearing? Remove the oil seal and just fit the top hat to get a better view

Try fitting the top hat, then position the crank weight and basket with chain onto the shafts without the hub and push the basket against the top hat, turn it to tension the top of the chain and check the chain run

Some pictures of the parts might help


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If I definately have the correct 13mm clutch spacer,the only other way to move the clutch in board would be a narrower clutch basket bearing.But that would make the basket circlip redundant.

Are you certain the clutch centre hub you measured,was from a known 159 year 1976,as I think it was only manufactured for 1 year  ?

Short of useing 6 crankcase gaskets stacked together with 3 Bond,not really good engineering practice,it only leaves shortening the clutch spring pins,which look to be held in place by original welds. 

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The top hat came with the 159 engine that I have so I assumed it is the correct one. So are you saying the basket isn't fitting far enough on the shaft and the chain run isn't in line? I'm not sure where you are now

You could have the wrong basket, the engine I have in bits didn't have a basket with it. The inside edge of the cover plate should sit just inside the edge of the basket fingers

I have two engines with the clutches exposed at the moment, a 199b and a 151. As a guide, on both of them, the gap between the crankcase edge and the inner side of the basket teeth is 15mm

If you shorten the clutch spring studs you will never compress the springs enough to fit the pins and clutch action would be seriously heavy. That's not the way to go, there is a fundamental problem somewhere. Previous owners could have done anything to this engine over the last 40 years

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If I use the inside face of the flywheel as a fixed datum point,as the flywheel cannot go any further inboard on the crankshaft  and only clears the crankcase by maybe 1.5mm. The chain runs inline to the clutch outer basket ok.

Yes the clutch pressure plate sits flush with the top of the clutch outer drum fingers,with 12 plates fitted.

The measurement you just said,from crankcase face to the clutch drum inside working surface ? of 15 mm. is usefull,I will check it tommorow.

Do you have a figure for standard length clutch springs please ?

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Springs are 24mm

If the weight is fully home on the crank and the chain line to the basket is ok, then that should eliminate the basket and spacer as a problem, if either was wrong the chain run would be out. 

Which brings us back to the hub. Is it definitely fully home in the basket bearing with the back of the hub right up against the basket. I'd remove both from the engine and just seat the hub into the basket and make sure it is going fully home. Sometimes they are tight and won't push fully home by hand and need a sharp tap

Something that can happen (if the clutch plate order is drive plate first) is that a drive plate can stick to the basket when plates are removed as probably most people do the same thing when removing the plates which is grab the tabs of the inner most plate and remove the pack as one - it's possible for the first drive plate to remain stuck to the basket. If the hub is then removed and the basket left in situ, the drive plate can slide downwards in the basket and if the hub is refitted it prevents the hub from fully seating. This is a proper long shot but it can happen

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Been following this thread and have to agree with Woody.  If the primary is full seated and the primary chain is perfectly in line with the basket - exactly parallel with the edge of the case when looking downward over the chain - then the culprit HAS to be the clutch hub not fully seating.  I don't recall from memory if the shaft on a 159 is splined or if the hub is held in position via a keyway, but it's possible either the key isn't lining up properly and stopping the hub from landing home or, if splined, if some material is preventing the hub from sliding into its fully seated position.  It helps to take some tension off of the primary chain when positioning the clutch hub by securing the chain tensioner with zip ties to the frame (if still in the frame) or via similar method if out.  That will reduce the lateral pull caused by the tensioner when positioning the clutch hub with its key or splines... and wlll make it easier to guide the hub straight through the basket bearing into its fully seated position.  

Out of curiosity, have you tried sliding the hub onto the shaft without the basket to test whether or not it's somehow getting hug up?  Give it a shot and take a measurement of exposed shaft threads, then compare that reading to exposed threads with the basket in place.

Hang in there - you will defeat this problem!!


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10 hours ago, Phillip1 said:


Hey Phillip,

Looking at this photo, it appears that clutch spacer is either not seated properly or is too long (+ 5mm, I'm guessing from the look of it). From memory, I believe my spacers typically sit nearly flush with the top of the seal once seated.  Yours appears to have significantly more clearance than I recall. This would certainly move the clutch assembly outward as you describe... but you also said the primary chain is presently in line with the flywheel primary?  Could it be that you have two spacers (clutch and primary) that are of incorrect lengths if this is so?

Time permitting I may pull the clutch from my 159 spare to measure what I have. I'll let you know what I find soon.

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That inner basket is the wrong one for a 159. A 159 should have nuts to hold the clutch springs in not pins. I think most of the later Sherpas all use the same clutch but I`m not sure when they changed from the pins to the nuts. But any clutch inner basket that used nuts should work.

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11 hours ago, Phillip1 said:

Woody can you confirm the measurement from crankcase face,to clutch outer drum inside face,that you said is 15mm. ?

Checked mine and got 29mm



The 15mm was measured to the inside edge of the basket teeth which is the closest surface to the case edge.  Measured to the inner edge of the actual basket drum, yes that's 29mm

You spacer looks correct to me as they don't sit flush up to the seal and if the chain. The positioning of everything else looks correct in this photo as well

The way the hub sits in the basket looks ok from the pictures, so at the moment I'm stumped as to why there is a problem with the case fit

The inner surface of the basket, which the hub sits against. Is this a completely flat surface or is there an inner recess into which the hub locates?

Have you tried just fitting the hub onto the shaft on its own (it won't go all the way onto the shaft) and fitting the case? Is there clearance then?

Try fitting the case (both cases) without the hub or basket and check the fit and see whether the splines on the gear shaft are fully visible which will at least eliminate a case issue, but as far as I'm aware there aren't different dimensions in that area for any of the cases

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