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Bearing clearances

Engine Building Fundamentals

Discussion and questions related to the course Engine Building Fundamentals


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How would you adjust the bearing clearance to a looser clearance if you are running the factory size crankshaft. Do you just select the bearings with a 0.001 bigger size? I only have seen like 0.010 Or 0.025. Thanks

i know with ACL bearings HX are additional 0.001" clearance.

depends on the engine though. most aftermarket supported engines have th HX options and im sure other quality bearing brands will have it too.

If you can buy graded bearings for your particular engine then this is a cost effective option. If you're trying to increase clearance slightly then you may be able to have a machinist polish the crank journals to achieve your desired clearance.

We did this routinely on S65 and S85 engines before larger clearance bearings became available. Send it to a crank shop and have the additional clearance ground and/or polished off.

As Andre said, with some more common engines there are sometimes hells available either side of the nominal size - if you mix and match halves for clearance, put the 'tighter' half in the connecting rod side or main bearing cap, as required.

If you need to polish it, just make sure it is a reputable mechine shop - as a 'prentice the local auto' machine shops were less than acceptable (IMO) as I have mentioned elsewhere. We had one crank's mains 'polished' and checking during assembly found they had given it 5 thou' clearance - boss said to put it together anyway... result? No idle oil pressure and a strip down and reground crankshaft. Sadly, that sort of thing wasn't that unusual but they were 'just' fleet rebuilds, so it wasn't as critical as the engines you guys are building.