Originally Posted by kingtal0n

All I heard was, aftermarket are better and softer, but use OEM bearings anyways.

Originally Posted by KCS

The OEM bearings are actually harder than the aftermarket bearings, not the other way around. Both bearing types typically have a steel back to them, but OEM bearings usually have an aluminum-silicon layer on top of the steel where as an aftermarket bearing has a layer of a lead-tin alloy, followed by a top layer of babbit. Babbit is very soft. If you're checking your clearances with a dial bore gauge, you should see that even the lightest touch with the anvil and fingers of the dial bore gauge will leave marks in the babbit where with an OEM bearing, there's nothing. That soft babbit layer is more forgiving for dirt and debris in your oil as well as scanarios where the oil film can't keep the crank and bearings from rubbing.

Aftermarket bearings also have some geometric differences to them too. They're designed with more crush compared to the OEM equivalents. Crush is what secures a bearing in its bore and keeps it from spinning with the crank. In the case of an aluminum block, it will help retain the bearing with elevated operating temperatures and the inherent increase of main bore diameter.


Compared to OEM bearings, the aftermarket also has a different eccentricity profile in the ID of the bearing. Bearings ID's are not perfectly round, they're oval, which is why you check clearance at 12 and 6 o'clock. If you check the diameter closer to the parting lines, you will see the diameter get larger which serves as a reservoir for oil. When the crank spins, the surface of the crank picks up oil from this reservoir and squeezes it into the tighter clearance creating the high pressure film that separates the crank journal and the bearing.

Those are the main differences, but in the type of stuff you see on here and in YouTube videos, I don't think you can really appreciate the advantages of a race bearing over OEM. Those aren't real race engines. The OEM parts are really good, and I think it's more common to fail the OEM rod or piston before you reach the limit of the OEM bearings. For that reason, the 5.3L I'm building for my car is going to be turbocharged and I decided to reuse some OEM main bearings from a Gen V LT1 and rod bearings from an LSA.

Originally Posted by lsswapnotch

I know this is an old thread but do you have part # for bearings??

Originally Posted by KCS

The OEM bearings are actually harder than the aftermarket bearings, not the other way around. Both bearing types typically have a steel back to them, but OEM bearings usually have an aluminum-silicon layer on top of the steel where as an aftermarket bearing has a layer of a lead-tin alloy, followed by a top layer of babbit. Babbit is very soft.

Originally Posted by lsswapnotch

I know this is an old thread but do you have part # for bearings??

Originally Posted by 01FormulaTA

89017571 - Main Bearing X 4
89017572 - Thrust Bearing X 1
89017573 - Rod Bearing X 8