How do you measure crankshaft bearing clearance?

By now, you will have the specs on the crankshaft mains and rods, the journals for both, and the specs on the bearings. Subtract the crank spec from the journal spec, and then subtract the bearing spec from that result. This figure is the clearance.

What should main bearing clearance be?

As a rule of thumb, main bearing clearance should be targeted between 0.0025- and 0.0020-inch for most street and street/strip engines.

How do I know my main bearing size?

The commonly accepted rule that most crankshaft manufacturers prefer for street and performance engines is 0.0010-inch for every 1-inch of journal diameter. So for a 2.45-inch small-block main journal, the bearing clearance would be 0.0024-inch.

What is connecting rod clearance?

A loaded connecting rod at peak cylinder pressure will reduce that oil film clearance to as small as 0.0002-inch. With a static bearing clearance of 0.002-inch that means the upper half of the rod bearing has 0.0198-inch worth of clearance.

How to check the clearance of engine bearings?

In order to check the clearances for rod and main bearings, you need a set of micrometers and a dial-bore gauge. These are readily available at budget prices, but if you are going to use them a lot, better quality tools are advised. This looks like a horseshoe with a round handle attached to one leg.

Is the thrust clearance on the crankshaft correct?

One of the clearances inside the engine that’s often overlooked is the thrust clearance for the crankshaft. While the thrust bearings are a little more forgiving when it comes to clearance than the other engine bearings, we still need to confirm that the clearance is correct.

How big are the holes in a crankshaft?

The dial bore gauge measures the inside of round holes, such as the bearing journals. This one tool can measure 2″ up to 6″ diameter holes. Both tools are needed in order to check the interior and exterior dimensions of the crankshaft, rods and engine block journals, as well as the thickness of the bearings themselves.

Do you need a caliper to measure bearings?

Even though bearings are flat enough, they cannot be accurately measured with calipers, instead you need a micrometer. There are special micrometers available for measuring round inside surfaces, but you don’t have to have one of those. Instead, you can use the shaft of a drill bit (good quality, and use the smooth part, not the fluted section).

How do you measure crankshaft bearing clearance? By now, you will have the specs on the crankshaft mains and rods, the journals for both, and the specs on the bearings. Subtract the crank spec from the journal spec, and then subtract the bearing spec from that result. This figure is the clearance. What should main…