Which plastigauge measurement would be acceptable for crankshaft bearing clearance in a highway diesel engine?

• A. 0.002"
• B. 0.020"
• C. 0.0002"
• D. 0.200"

Answer: (A)

Plastigauge is used to measure bearing clearance by placing a marked plastic strip between the crank journal and the bearing. After torquing the cap to spec and removing it, you read the width of the flattened strip against its scale to determine clearance. For a highway diesel engine, crankshaft bearing clearances are typically a few thousandths of an inch, roughly in the 0.0015 to 0.0030 inch range. A reading of about 0.002 inches falls squarely in that acceptable range, indicating the journal is properly spaced from the bearing to allow a film of oil without excessive looseness.

A reading around 0.020 inches would be far too loose, risking oil pressure loss and knocking. A reading as tight as 0.0002 inches is typically too tight for a lubricating film and could cause bearing scuffing or seizure. A clearance of 0.200 inches is far beyond any acceptable tolerance and would be catastrophic for oil control and bearing life. Always compare the measurement to the engine’s specified tolerance in the service manual.