Up Service Manual FAQ Favorites Photo Gallery

Crankshaft Inspection and Repair

Tools Needed: Balancer or chuck stand, two 1" dial indicators, dial indicator stands, 15 mm deep socket and feeler gages.


You will need something to hold the crank. Here I have the crank on my Rod Neff balancer. You can chuck it up in a lathe or think up some other simple way to suspend the crank.

A view from above. The left arm of the balancer is  adjustable in the vertical and the right arm is adjustable in the  horizontal. Both bearing heads pivot so walking of whatever you are balancing can be eliminated.

Close up of crank on balancer.

Use a set of feeler gages to measure the axial play between the rod big ends and crank cheeks

The axial play should be between .008" and .013" (0.20/0.34 mm).

Check the trueness of the rod arms by slipping a 15mm deep socket between the rod small ends. The socket should slip through without binding. If it binds, at least one rod arm is bent.

How's this for balance?

Here is an example of an obviously bent rod arm. The socket will not go through the small ends. A crank with a bent arm is not repairable and must be replaced.

Using the 15 mm socket, set up a dial indicator as shown and measure the turning of the crank pin. Measure the crank in two spots. If the tolerance exceeds .020" (0.50 mm) between the two measurements, the crank will need to be replaced.

Next, check for radial play of the connecting rod.

To do this properly  the crank should be chucked up at the ends so it does not move. Once secure, set the dial indicator up on the big end of the crank arm and while grasping the small end push toward the dial indicator. If the radial play of each arm exceeds .004" (0.10 mm) the crank should be replaced.


To measure the run-out of the crank, set up a dial indicator on each of the main journals...

...turn the crank and watch the deviation of the needles. The needles should deviate in the same direction; both positive or both negative. The maximum permissible run out is .020" (0.05 mm). If the dial needles go opposite of each other the crank needs to be replaced.



Up Service Manual FAQ Favorites Photo Gallery