Plastigage can be used as a quick way to check clearance. To use plastigage correctly, first
assemble the upper bearing shell into the housing, then install the crankshaft. Lay a strip
of plastigage lengthwise across the center of the bearing journal. Install the lower bearing
shell and cap, and tighten the fasteners to the specified torque. Loosen the bolts and
remove the bearing cap and lower shell, being careful not to rotate the crankshaft.
Compare the thickness of the now compressed plastigage strip to the chart on its package
to determine the bearing clearance. Carefully remove all traces of plastigage from both the
crankshaft journal and the bearing before final assembly.
High performance applications may require different bearing clearances than unmodified
engines. Many engine builders target a clearance range between .0022" and .0027".
Clearances greater than .003" are not normally recommended. Some engine builders like
higher oil pressures than a standard oil pump can provide, particularly at lower engine
speeds. Large bearing clearances will lower oil pressure, and may require a high volume
oil pump. An engine should maintain a minimum oil pressure of 10 lbs. per 1000 RPM.
Plastigage is also used by machine manufacturing for checking clearances. Pumps, Generators, Industrial equipment of all kinds can be checked using this procedure. Also used in the injection mold businesses.
|Individual Piece Length (in)
|Maximum Clearance (in)
|Minimum Clearance (in)
||Sealed Power Plastigage