how to know which main bearing and rod bearings to buy?

[kickinindian]

Im using an m52b28 crank in my m20 block with stock b27 rods. so im just wondering should i just buy standard size bearings or get .25mm oversize? or how could i measure it to know before hand? first time building an engine so kinda paranoid to get it right.

[jlevie]

Measure the crank journals (to a tenth) and use the clearance table in the Bentley or TIS to pick the bearings.

[SkiFree]

If you're paranoid on getting it right and a first timer I'm sure you're getting the crank and rods checked out by a machine shop. They'll tell you if the crank needs to be ground undersized and if your rods need to be rebushed.

[kickinindian]

So torque the journal caps to spec and measure the gap? Same with rods? Without the old bearings

[bmwstudent]

You measure the rod and main journals on the crank. You'll need a micrometer that reads to .0000 or better. Make sure you make at least a couple measurements on each journal to make sure they are round. You still might want to take it to someone to have the journals polished.