engine bearing clearances
 

one thing I never see discussed is engine bearing clearances.

what are the stock specs?

what are the preferred performance specs?

If i'm not mistaken the factory tolerances are in the .0005"-.0015" range. Typically most high hp applications like more tolerance and a thicker weight oil. This is to allow for more buffer(thicker pad of oil) due to the extra loads. .0025-0035 is typical for race apps and use of at least a straight 30 weight oil, sometimes as much as straight 50 weight. Big block chevy's tend to require .003-.005" oil clearence on the crank. This is because of the extra weight of the rods and pistons. These extreme tolerances are not usually used in an everyday street application. They require high volume oil pumps and high pressure springs in the relief valves in order for it to supply enough oil. This also requires larger oil pans for more volume to prevent sucking the pan dry. I'm just recalling from memory with the #'s so someone feel free to step in and correct me.

LQ4/LQ9/LM7/L59/LR4/L33 stock specs
Connecting Rod Bearing Clearance (Production)
0.023-0.065 mm
0.0009-0.0025 in

Connecting Rod Bearing Clearance (Service Limit)
0.023-0.076 mm
0.0009-0.003 in

Crankshaft

Crankshaft Bearing Clearance (Production)
0.020-0.052 mm
0.0008-0.0021 in

Crankshaft Bearing Clearance (Service)
0.020-0.065 mm
0.0008-0.0025 in

i concur lol. same in my 04 manuals.

If I remeber correctly the bearing tolerance on my crank in my 418 is ~.0025 or so mjhoward actually checked it I just watched, maybe he remembers.

Anything over .0025 on the mains and you are gonna have oil pressure probs. I have experimented with this a little and I am liking .002 on the mains and rods. These engines don't need the excessive clearances like the old SBC and BBC's did.

.002-.0025 is what your entire engine ranged(rods and mains).

Here's a thread that I started on optimal clearances about a month ago on LS1Tech.com. See https://ls1tech.com/forums/showthread.php?t=431003. There were a number of good responses.

Steve

very good data, thanks for the link :judge: :)

i put my mains @ 3ths and rods @ 3.5ths