chrisfrost

iTrader: (8)

Hello poeple , My question is preferably for the proffessional exp engine builder or anyone whom has rebuilt at least a few LS's . The rod bear oil clearance in My repair manual says desired .0009" - .0025" . Now I assume a brand new GM LS engine to be at the .0009" clearance with the desired max being .0025" and the absolute max being .0030" . These #'s are total clearance in other words .00045" all the way around the inside between the bearing and the rod journal? unless of course the rod is pushed against 1 side or the other which would put the whole .0009" or most of to the opposite side . Reason I'm asking 1. is because it seems to me that plastigage on 1 side would pull the rod closer to 1 side while it was in there kinda making the reading less than accurate unless it pulls the rod as far as is possible without screwing up the bearing , then I would say it would be fairly accurate . 2. What do machine poeple do rely on their measuring equipment which is usually more accurate than what most of us have ?

94mustang

iTrader: (1)

.0009" never! Rod bearings should be from .0021" - .0028" This is total clearance. Dial bore guages are your friend here. plastiguage will work, but is not the preferred method.

KCS

iTrader: (20)

Yes, that's total clearance as in the shaft OD should be X bearing clearance smaller than the bearing ID. The plastigague measures this total clearance.

Machinists use more expensive and more accurate instruments to take measurements, typically dial bore gauges, micrometers, and dial calipers.

Don't go by the service manual for bearing clearance if you're building a high performance engine. Go one to Clevite's website and look through their Publications section. You'll find a lot of tech info regarding bearings and clearances, probably more than you'll really ever need to know.

chrisfrost

iTrader: (8)

I've read Clevites bearing failure page but their bearing clearance stuff is a little hard to extract the info I need from . Thanx for the replies .
BTW my build is'nt anything crazy just LM7, hand ported 706's , flat tops and LS6 cam , tune, shorties and probably 2.5" to the axle into single muffler until I can afford some real exhaust

A.R. Shale Targa

iTrader: (2)

If you're having the crank polished by a local macine shop it's good to have
it measured with a micrometer so you know its current state of wear and
can impress to said shop to use a very fine or used belt so as to not remove
much material. The preferred meathod is to measure the rod journal after
polishing with a mic, lock the mic, then use that number to set the dial-bore
guage and zero it in. Then put your new bearing shells into the big ends of
the rods and torque the bolts. Be certain to closely inspect the bearings for
burrs on the babbit side as well as the backing ( sometimes packaging can
cause issues ). Then use the bore guage to measure the inside bearing
diameter....the guage will show you the exact number. I shoot for .0017-
.0023...Good luck !!!!