Main Bearings?

[cardboard]

My son wants to drop his oil pan and put a set of main bearings in his 4.0 to see if maybe that will quiet it down for awhile. My question is , Do we go back with stock bearings or do we go oversize?
Digger

[jeepcherokee95]

Only way to know is use some plastigauge or "mic" (sp?) the journals.

How many miles?

You may be able to just go back with stock since the old bearings are "worn" some but some kind of measurement is needed I am sure.


JC95

[Eagle]

First, on the 4.0L it is usually the rod bearings that need to be replaced rather than the mains. Second, check the build code stamped on the side of the block near the distributor. Some engines came from the factory 0.010 under on crank and/or rod bearings. If you have one of those, putting in standard bearings would make things worse rather than better.

Other than that, I would throw in whatever size came in the engine. Some people advocate using replacements that are 0.001 smaller (dealer only, I believe), but that's probably not necessary.