Main bearing clearance
Moderator: Team
Main bearing clearance
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?
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?
-
- Guru
- Posts: 6382
- Joined: Tue Jul 24, 2012 11:15 am
- Location: Roseville, Michigan (just north of Detroit)
- Contact:
Re: Main bearing clearance
In my opinion, to much for anything except a high torque/horsepower drag race application.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?
http://www.rmcompetition.com
Specialty engine building at its finest.
Specialty engine building at its finest.
-
- Pro
- Posts: 205
- Joined: Mon Feb 04, 2019 2:23 pm
- Location: california
Re: Main bearing clearance
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.
- mt-engines
- Expert
- Posts: 871
- Joined: Fri Sep 27, 2019 12:35 pm
- Location: MN
Re: Main bearing clearance
With a wobbly block and 4" mains.Walter R. Malik wrote: ↑Wed Feb 12, 2020 4:34 pmIn my opinion, to much for anything except a high torque/horsepower drag race application.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?
-
- Guru
- Posts: 1745
- Joined: Tue Jan 15, 2013 8:10 pm
- Location:
Re: Main bearing clearance
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.
If the bearing crush is compromised (oversized bores), that is not a good thing either.
Maybe worse than an extra 0.001" bearing clearance.
Re: Main bearing clearance
Big block Olds with factory crank...you need that or it will tear itself up.
Re: Main bearing clearance
Dan I agree completely, the hack job the machine shop did was pretty ridiculous.
-
- Guru
- Posts: 1758
- Joined: Wed Aug 26, 2009 8:30 pm
- Location: Beautiful Southern Maryland
- Contact:
Re: Main bearing clearance
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 ?
Bill Koustenis
Advanced Automotive Machine
Waldorf Md
www.enginerepairshop.com
Advanced Automotive Machine
Waldorf Md
www.enginerepairshop.com
Re: Main bearing clearance
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.
Re: Main bearing clearance
What is the main bearing housing bore size, that may help on the bearing clearance issue.
Re: Main bearing clearance
It was 2.6440 to 2.6450 after the machine work on every journal after machine work.
Re: Main bearing clearance
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.
-
- Guru
- Posts: 1264
- Joined: Fri Feb 26, 2010 11:15 am
- Location: Gold Canyon, AZ
Re: Main bearing clearance
Yes, .004" is too much main bearing clearance for SBC. Select main bearings that will give you around .003" clearance.
Bill
Perfect Circle Doctor of Motors certification
SAE Member (30 years)
ASE Master Certified Engine Machinist (+ two otherASE Master Certifications)
AERA Certified Professional Engine Machinist
Perfect Circle Doctor of Motors certification
SAE Member (30 years)
ASE Master Certified Engine Machinist (+ two otherASE Master Certifications)
AERA Certified Professional Engine Machinist
Re: Main bearing clearance
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.