Checking the Crankshaft

I picked up a 400 sbc at the wreckers for $100. The crank had spun 2 rod bearings which will need to be ground down.


Top rod bearing is spun pretty bad and 2nd from top was spun but is okay.

The crank rods were ground 0.020" and the mains had to be taken down to 350 size of 2.450" from the std 2.650". I'm using spacer bearings which allows a 350 crank in a 400 block. Usually used to make a 377 cid.

plastic gauge

The crank was installed, main caps torqued to spec with plastigauge.

- I plasti-gauged the main bearings to verify clearances and found that bearing #1 (closest to the front) had a bad taper of 0.001" clearance at the rear of the bearing and 0.003" at the front. I measured it twice just to make sure that I didn't squeeze the plasti-gauge removing the cap. This means that the block needs to be align honed.

Match the width of the flattened Plastigage with the paper reference to determine the clearance

The crank was installed, main caps torqued to spec with plastigauge. I cleaned up the plasti-gauge and oiled all the journals. Reinstalled and checked to see if the crank by chance would spin easily. Spinning easily are not the words I would use! It definitely needed to be align honed. So off to the machine shop it went.

- Tip of the Month! Don't buy a stuck block, you are asking for trouble. If it can't spin then it's going to take lots of work and money to get it back up to working condition and maybe it won't ever make it.

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Copyright May 2011 Eugene Blanchard