Crankshaft Diagnosis

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Crankshaft Diagnosis

When removing a crankshaft its important to mark the bearing caps before
removal. Most main bearing caps are marked with a number and directional
arrow but make sure they are present and if not make your own.

Crankshaft end play is measured with a dial indicator mounted on the engine
and the indicator on the crankshaft flange. Use a pry bar or a large screwdriver
to move the crankshaft back and forth. Its important to check the specifications
and clearance should be minimal a few thousandths at the most.

An outside micrometer is used to check for crankshaft journal wear. Check both
around and along the journals for taper and out of round. Journals can wear at
the ends or in the middle. Check for roundness at least two different points, they
usually wear a one place TDC (top dead center).

When replacing the bearings make sure the oil holes in the block line up with
holes in the bearing. If the block or journal have been machined it may require
over sized bearings.

Always check the clearances with plastigage. Insert the plastigage in the center
of the bearing and then properly torque the cap. Measure the thickness with the
gauge on the package for specifications and note that any uneven thickness
indicates taper.

In summary if there is a sharp rapping noise especially at idle its probably the
crankshaft and it should be checked for crankshaft end play. In most cases this
can be achieved by mounting a dial indicator on the timing cover and the tip of
the gauge on the harmonic balancer.

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