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Main bearing clearances

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Hi all,

I have measured my main bearing clearances and the manufacturer recommends .001”-.0024” clearances. I am reading .0005”-.0008” over the upper tolerance.

I have looked and there are no different bearing sizes to accommodate this clearance. What do you think my options are?

What is the engine, and what do you intend to do with it?

You have several options -

a/ have custom shells made

b/ check the bearing manufactures if they have an undersize bearing available - KING have them for some popular engines.

c/ have the crankshaft reground to the correct size for next undersize shells

d/ use a heavier grade oil

e/ not worry about it if it's stock, or a mild power increase.

There is another very old method of increasing clearance a little bit but it requires knowledge and experience. It sounds scary but works 100 percent if you know how to do it. You take the upper part of the bearing half and slightly bang it with hammer, just a tiny bit. It will increase the overall clearance. I've been doing it on performance engines without any failure as well as filing bearings to bring the down to smaller clearance. Most people are afraid of doing that but i have positive experience with adjusting bearings shape- you just need to know the limit.

it's excessive clearance, Shota - I think shaving caps might be a bit too extreme for the chap, which is another trick..

Oh, sorry, I misread the numbers the other way around. For decreasing the clearance I shave off the upper side of bearings by fine griding stone to some extended- up to 0.04 mm overall clearance and remove sharp edges. It works well when there is no other option but again, it requires some experience as we know.

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