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Main bearing clearance

General engine tech -- Drag Racing to Circle Track

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Outlaw383
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Main bearing clearance

Post by Outlaw383 »

Have a friend that had a machine shop align
hone the mains. I've checked it with the bore guage and it's going to be about .004 clearance. I've never run anything with more than .003 This is strictly a race motor bit it's a circle track piece what do you pros think?
Walter R. Malik
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Re: Main bearing clearance

Post by Walter R. Malik »

Outlaw383 wrote: Wed Feb 12, 2020 4:27 pm Have a friend that had a machine shop align
hone the mains. I've checked it with the bore guage and it's going to be about .004 clearance. I've never run anything with more than .003 This is strictly a race motor bit it's a circle track piece what do you pros think?
In my opinion, to much for anything except a high torque/horsepower drag race application.
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novafornow
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Re: Main bearing clearance

Post by novafornow »

Is this a sbc or a big block cadillac? Application matters, but .004 is loose. For most combo's, it is too easy nowadays to get bearings that will make just what you want. I have ran that loose before though.
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Re: Main bearing clearance

Post by mt-engines »

Walter R. Malik wrote: Wed Feb 12, 2020 4:34 pm
Outlaw383 wrote: Wed Feb 12, 2020 4:27 pm Have a friend that had a machine shop align
hone the mains. I've checked it with the bore guage and it's going to be about .004 clearance. I've never run anything with more than .003 This is strictly a race motor bit it's a circle track piece what do you pros think?
In my opinion, to much for anything except a high torque/horsepower drag race application.
With a wobbly block and 4" mains.
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Re: Main bearing clearance

Post by Dan Timberlake »

What size are the main bores?
If the bearing crush is compromised (oversized bores), that is not a good thing either.
Maybe worse than an extra 0.001" bearing clearance.
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Re: Main bearing clearance

Post by gmrocket »

Big block Olds with factory crank...you need that or it will tear itself up.
Outlaw383
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Re: Main bearing clearance

Post by Outlaw383 »

Motor is a sbc.
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Re: Main bearing clearance

Post by Outlaw383 »

Dan I agree completely, the hack job the machine shop did was pretty ridiculous.
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Re: Main bearing clearance

Post by BillK »

Outlaw383 wrote: Wed Feb 12, 2020 7:09 pm Dan I agree completely, the hack job the machine shop did was pretty ridiculous.
How do you know that ? Have you measured the main bearing bores with a bore gauge ? How about the crankshaft journal sizes ? How about the bearing thickness ?
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Outlaw383
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Re: Main bearing clearance

Post by Outlaw383 »

Yes I measured it and micd the crank journal how could I come up with the clearance without doing that. How do I know that? Because I saw the hack job that the machine shop did.
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Re: Main bearing clearance

Post by Baprace »

Outlaw383 wrote: Thu Feb 13, 2020 7:57 am Yes I measured it and micd the crank journal how could I come up with the clearance without doing that. How do I know that? Because I saw the hack job that the machine shop did.
What is the main bearing housing bore size, that may help on the bearing clearance issue.
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Re: Main bearing clearance

Post by Outlaw383 »

It was 2.6440 to 2.6450 after the machine work on every journal after machine work.
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Re: Main bearing clearance

Post by n2omike »

As long as there is sufficient bearing crush, you can buy bearings that will tighten it up a thou. For a SBC, they should be available on every oversize. If the crank is ground 0.010", it would be a 0.011 bearing.
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Re: Main bearing clearance

Post by engineguyBill »

Yes, .004" is too much main bearing clearance for SBC. Select main bearings that will give you around .003" clearance.
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Outlaw383
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Re: Main bearing clearance

Post by Outlaw383 »

Thanks for the input guys at this point I think we will just put this in a different block and go with our normal .0025 to .003 clearance and do something with this block later on. Appreciate the responses.
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