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Phillip1

JM 159 clutch case depth ?

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My clutch case does not have any clearance and rubs on the clutch centre drum pins and the end of the clutch springs ?

Not sure if I have the wrong clutch centre hub,or the wrong clutch case ?

Year manufacture 1976.

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More information needed, methinks......

Is this a bike you have owned for some while (and had running), or a disparate collection of parts you are trying to assemble ?

When did the problem first arise ?

What parts have you replaced ?

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Recently purchased bike.Previous owner had attacked inside of clutch cover with angle grinder to gain clearance for clutch and nearly totally removed thread for clutch adjustment cap ! I have tried another clutch case and it hits the clutch pins and clutch springs,leaving a 6mm gap where the clutch case gasket goes.

Something is drastically wrong ?

Are there different clutch centre hubs with shorter pins ?

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Hello phillip1,

If you can wait 11 years Sherpa325 will have the information you need. It might take longer though, as you didn't put Urgent in your heading.

Is there an extra clutch plate fitted? That would space out the pressure plate. Or a thicker washer between the clutch basket and the inner bearing.

Brt650

Edited by brt650
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Hi Bert 650cc. ?

I would like to assemble shortly, as probably will be too old to ride if I have to wait 11 years !

Only 12 clutch plates used and clutch final cover plate ends up level with clutch outer hub,so clears casing ok.

It is the 6 clutch pins and springs that foul the clutch cover inside ?

Thank you for your URGENT reply ! 😁

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Hi Phillip,

As you say it’s the springs and the pins hitting, you would think maybe the basket or the hub are spaced out too far. 6mm is a large gap trying a different case.

You might need to pull it apart and check the chain alignment. Checking to see if the basket is out of alignment with the crankshaft sprocket. If it’s right, check the spacer thickness between the clutch hub and basket. I don’t have a measurement  for it.  

The later clutch assemblies use threaded pins and nuts. 

Cheers

Brian

 

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Hi Brian,

Just double checked the sprocket/chain alignment to crankshaft sprocket and is correct.

Also removed the flywheel ready to replace the crankshaft seals and checked flywheel was seated correctly on the shaft.

Is there another type of clutch cover that is deeper, as I just replaced the damaged one with what looked the same bare alloy finished type ?

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I've got a 159 hub in a box of bits so measured it as follows,  overall depth 43mm, depth of the hub where the plates sit 22mm.  depth of the boss at the back 21mm. Pin length 33mm, length of pin showing from edge of hub to end of pin 19mm.

Behind the hub is a top hat distance piece that sits between the bearing and the hub. This is 13mm.

These are also the measurements for the same parts fitted to model 80 and model 151. As far as I know, the hubs with the pins to hold the springs are the same on each of the Sherpas that used them, model 80 up to 159 type engine. Not sure about Pursangs though, they may be different

Is the top hat behind the hub the right length. Later engines with the threaded pins have a longer top hat although if one of those was fitted it might affect chain alignment. Also some hubs with threaded pins are a few millimetres longer in depth

Again, as far as I know all of the cases are the same in that area, the case shouldn't be a problem with the pins 

 

EDIT  -  I've just realised my use of the term pins might be confusing. By pins I mean the long studs that the springs and cups slide over, not the small roller pins that  hold and tension the springs. I should have just said studs...

 

Edited by woody
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Yes not all threaded clutch hub spring studs are the same length and also yours may have had the original studs replaced.

Also there is more than one length for spring buckets, but you said it was the studs hitting not the nuts hitting.

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I'm really hoping we have computers and internet in 11 years time when sherpa325 answers this question.

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There is a few different spacers that go behind the clutch and the primary drive. Different widths/ heights. I know a 158 primary drive will not fit a 151 engine without changing both spacers as it sat at a different height and the primary chain didn`t line up.

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Firstly thank you Mr.Woody for supplying all the figures for clutch and spacers.

So today measured my parts again and compared them to Woody figures.  They were all the same.

Then removed crank flywheel and checked its alignement to clutch sprocket,which was good.Flywheel position on crankshaft looked to be correct and could not be further inboard,as it only has minimal clearance to right hand crankcase.

Also checked clutch cover mating faces,incase they have been re machined flat.They look to have the original machining pattern.

So have eliminated having the wrong parts fitted,but still need to gain maybe 4mm.plus 1mm for clearance=5mm. ?

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A bit baffling this...  If you fit just the hub and spacer, nothing else and then try and fit the casing what happens?  The top hat spacer should fit inside the seal and up against the bearing, the hub then fits up against the spacer. Is there anything stopping the spacer locating against the bearing?

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Certainly is something wrong.

Yes the clutch outer,12 plates and clutch cover plate clear ok.

The top hat behind the clutch clears the crankcase by maybe 3mm,but does not appear to have been altered ,as it still has the recess for its "O" ring,which seals to the bearing.

One maybe relevant thing I noticed;There was a ball bearing under the clutch mushroom, but two more ball bearings came out with the clutch push rod.So 3 ball bearings in total,is that correct ?

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Only one ball and that goes between mushroom and pushrod, but maybe the wrong pushrod is fitted and is too short. However, even if the overall length of the rod and balls is too long it can't affect the position of the spring studs as they are fixed on the hub which is not affected by the pushrod,

If you leave the basket and plates off and just fit the hub and spacer, nothing else, what happens with the casing then? 

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