Author Topic: B31 Primary drive  (Read 429 times)

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B31 Primary drive
« on: 15 June, 2017, 23:13:21 »
Hi all, more advice desperately needed!
I am into the primary chaincase, the strip down going well, clutch removed and them I noticed the primary chain has been wearing the main bearing housing extrusion. Please see photo.
My initial thoughts.
-Is the sprocket too small? It has 16 teeth, I presume more teeth would give a bigger diameter and thus more clearance.
-Is the primary chain wrong and had a chain fitted that's too wide?
-Or maybe the problem is the sprocket does not have enough shims behind it to give clearance?
-The corks on the clutch basket are just about non existent - would this have an effect?

And finally, any tips on removing the shock absorber nut, I am hoping a C spanner will tackle the job, but it looks like it has had a fair bit of hammer in the past. Is it a left hand thread? I seem to think there is a 'lefty' associated with the 'bottom end' somewhere.

Once again, many thanks for any advice.

PS, Just down loaded the photo from my phone and almost cr****d myself. I thought there was a crack in the cases and after a frantic run back to the shed the crack turned out to be a piece of cotton from a rag!


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Re: B31 Primary drive
« Reply #1 on: 16 June, 2017, 10:19:14 »
Usual sprocket for B31 would be 17 teeth.

Is that damage recent - you would find traces of aluminium in the drained oil - or something historic?

Any shims behind the sprocket would be to align it with the clutch chainwheel.

The nut is normal right hand thread. There is (or should be) a lock washer under the nut. Usually nut very tight for obvious reasons and often tightened up with a hammer and drift. You may need to resort to this method especially if the nut is damaged.