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myson

Crankshaft rebuild

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Hi, I am slowly progressing with my M80 rebuild and I am splitting cranks to replace gearbox shortly. I am considering having the crank rebuilt with new bearings but most kits include a new conrod. This adds a lot to the cost when budget is limited! Is it feasable to rebuild using the original con rod with new bearings or is there a good reason for replacing everything? Also, can any one recommend a good engine guy in Newcastle/Durham area to carry out the rebuild?

Cheers,

Myson

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If the bearings are OK You can still use the old conrod,

BUT:

If you turn the conrod by hand and the bearings feel kind of harsh while moving (difficult to explain),

not smooth and without any feelable resistance, than it's time to exchange.

Damages to the bearings can emerge just because the engine had stood too long without being driven.

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If the bearings are OK You can still use the old conrod,

BUT:

If you turn the conrod by hand and the bearings feel kind of harsh while moving (difficult to explain),

not smooth and without any feelable resistance, than it's time to exchange.

Damages to the bearings can emerge just because the engine had stood too long without being driven.

Thanks for the reply, the bearings feel fine I ws just thinking of doing the job while I had the cranks split, may save a job later on, I was going to have a new big end bearing fitted to original con rod if possible,

Myson

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Personally I would always change the whole thing, not just bearings.... :closedeyes:

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On a rebuild all bearings must be within limits. To check a bigend assembly, there must be no up and down play, sometimes sideways play can be confused for the up and down play, so check very carefully, any up and down play whatsoever is suspect. Sometimes the bigend assembly can be saved, by just changing the pin and roller bearings, as the pin has to work twice as hard as the rod itself. Rods can sometimes be reconditioned if a replacement isn't available, by firms such as Alpha. But i'm sure Bultaco Uk would probably have a rod assembly.

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