What is the difference between oversized and undersized on a rod bearing?

An undersized bearing has extra material thickness on the inside of the bearing facing the crankshaft journal. Oversize bearings have more material on the outside facing the bearing housing bore. Oversized bearings are used when the block has been machined or line bored oversized.

What is the standard rod bearing size?

These bearings generally come in four sizes: standard, . 010 oversize, . 020 oversize and . 030 oversize.

Why are rod bearings undersized?

Journal scoring or scratching as a result of oil contamination is common. To restore the journals to stock smoothness, machinists remove just enough material from the journal surface to eliminate the deepest scratches. Undersized bearings compensate for the amount of material removed during this machining process.

What should rod bearing clearance be?

The factory specs include 2.450-inch main bearing journals and 2.100-inch rod journals, which means the target bearing clearance should be about 0.0024-inch (0.0025 is the common spec) on main bearings and 0.0021-inch on the rod bearings.

What happens if rod bearings are too loose?

On the other hand, if the tolerance is too loose you hemorrhage oil out from around all the bearings. Obviously, too loose is better than too tight, but hitting the center of the bullseye is always preferable. So for a 2.100-inch rod journal, it’s always a good idea to shoot for 0.0021 or 0.0022 bearing clearance.

How do you know what size bearings to get?

You can measure the dimensions of a bearing by using a vernier caliper like the one below or measuring accurately with a ruler. All bearings will have an inner diameter (ID), an outside diameter (OD) and width (W). Bearings are sometimes referenced by these dimensions, in that order: ID x OD x W.

How is connecting rod bearing clearance measured?

For these reasons, bearing clearances are specified as “vertical clearance” and must be measured at 90 degrees to the split line. The best method of measurement is with a dial bore gage that measures the bearing inside iameter when the bearings are installed at the specified torque without the shaft in place.

How accurate is Plastigage?

Well, Plastigauge will get you in the ballpark but isn’t as precise as using “proper” measuring tools. On paper, a . 0002 to . 0004-inch difference doesn’t sound like much, but that is a 9- to 18-percent difference in accuracy.