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Old 01-26-2017, 12:30 PM   #2
SeaSlugs
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Location: Central, IL
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Default Re: Platigage and bearing clearances

Quote:
Originally Posted by Bob Johnson View Post
I have read lots of opinions on how to check main and rod bearing clearances. There is something that confuses me. It is generally agreed that there should be 0.001" of clearance for each 1.0" of bearing diameter. On a B engine the main bearings are about 2". That would result in a bearing clearance of 0.002". The confusion, for me, is the following. Should the bearing be 0.002" larger than the crank journal? For example, bearing 1.999" and crankshaft journal 1.997". Or is that clearance a 0.002" gap all the way round the journal. Which would make the example bearing 1.999" and the journal 1.995"?

With regard to Plastigage. I have read conflicting instruction. Most say use one piece across the journal. There were also instruction to place two pieces across the journal 180 degrees apart. The first method would give an 0.002" difference (0.001" overall gap) between the bearing and the crank. The second would give a 0.004" difference (0.002" overall gap).

I have tried both and the 0.004" difference (0.002" gap) appears to be too much. The crank can be moved up and down producing a rattle noise.

What do you guy think?

Bob Johnson
plastigauge you use one strip, it creates a high point so to speak that gets flattened when things are tightened/torqued. then remove the journal and see how far it got flattened - thats your clearance.

to check for roundness yes use it 180* apart but do one strip at a time - do one side get a result and record it, get the plastigauge off 100% clean, then do the other side, get a result and record it - ideally they should match but most likely they wont unless it was fresh bored. take an average and adjust shims accordingly
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