Bearing Clearances for an SBC

[73 Mike]

I'm starting to assemble my 412 SBC and would like to check the clearances. I'll probably use plastigage as I don't have a good inside mic.

I need a target clearance to order the bearings but would like to know the tolerances as well.

Based on this article among others:

http://www.chevyhiperformance.com/tech/engines_drivetrain/shortblock/4380_bearing_clearance_info/

looks like 2 thou is about optimal for both crank and rod. What says Vettemod?

Particulars:

4.185 bore
3.75 stroke
Motown block with priority main oiling
HVRP oil pump and oversize pan
Hydraulic retrofit rollers

 

[GT6Steve]

I've always heard rule of thumb is 1 thou per inch of journal. I don't have ANY specific knowledge on Chevy's though...

 

[TimAT]

A link:
http://www.small-block-chevy.com/assemblyspec.html

 

[Belgian1979vette]

I've always heard rule of thumb is 1 thou per inch of journal. I don't have ANY specific knowledge on Chevy's though...

Very correct.

 

[73 Mike]

Thanks guys, that helps. Just to confirm, the bearing clearance is total, not per side.

A link:
http://www.small-block-chevy.com/assemblyspec.html

Thanks Tim, that's a pretty cool link. Lots of useful info plus I can print the page and have it by the motor when I assemble it.

 

[TimAT]

Be sure and check the rod side clearance- easy to forget, and if the crank radius is off a little it will push the rods together. Same with crank end play. Normally it's OK, but still worth checking.

 

[Belgian1979vette]

Be sure and check the rod side clearance- easy to forget, and if the crank radius is off a little it will push the rods together. Same with crank end play. Normally it's OK, but still worth checking.

It's not worth checking, you absolutely need to check it. If rod side clearance is not correct you will get no oil to the wrist pin and you can probably guess the rest. Oh and don't install the bearings correct.