Author Topic: Crankshaft Bush  (Read 1133 times)

Offline namloop

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Crankshaft Bush
« on: 17.07. 2012 01:46 »
Hi to all
My engine is in many parts and I have noticed the plating/surface of the crankshaft bush is lifting slightly.
There is no gouging or scoring or marks of wear.
Can this be replated and if so with what?
Alternatively if I change the bush for a new one I assume it absolutely necessary to have the piece line bored.
Would I supply both halves of the case bolted together with the piece in situ with the bearing?
Any answered welcomed.
Regards
Stephen

beezermacc

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Re: Crankshaft Bush
« Reply #1 on: 17.07. 2012 08:29 »
The bush is usually made from solid phosphor bronze or steel with a white metal on copper or phosphor bronze liner. The surface lifting you describe is unfamiliar to me but I suspect is undesirable! You should check your crankshaft journal for ovality; ovality up to 0.0005" (1/2 thou) is acceptable, maybe up to 0.001" for steady use is OK, anything over 0.001" I would get the crankshaft ground back to round. I would advise using the solid phosphor bronze bush which can be purchased in various undersizes. As it is solid you can line bore it to suit the crankshaft size without needing to stick to the 010 graduated undersizes. The bush will need line boring. A good engineering workshop can undertake this for you. They will need both crankcase halves and the bush. I dare say they could fit the bush if you asked them. I usually do this job myself with an expanding hand reamer and a guide working from the left hand crankcase. It is a bit tricky and time consuming - not everybody would approve of this method- but I have bored numerous bushes with excellent results.

Offline Goldy

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Re: Crankshaft Bush
« Reply #2 on: 17.07. 2012 09:46 »
If there is any uncertainty with the bush then it needs to be renewed. Don't get the bush that is steel with a bronze liner. C and D do an all bronze bush about 60 thou undersized. Heat the cases in the oven before fitting the new one. Most precision engineering companies will bore it for you, but remember its just a small job for them and they may just want to fit it in when they have a window, so times given are usually a bit optimistic .
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