What tool is generally used to measure crankshaft bearing journals?

• A. Vernier caliper
• B. Dial indicator
• C. Outside micrometer
• D. Straight edge and feeler gauge

Answer: (C)

Measuring an external cylindrical dimension with high precision is best done with an outside micrometer. The crankshaft bearing journal is a precisely sized external cylinder, and you need a reading accurate to thousandths of an inch (or hundredths of a millimeter) to determine the bearing clearance correctly. An outside micrometer uses calibrated screw motion between two anvils to squeeze the journal and read its diameter directly, giving you a reliable, repeatable measurement.

Vernier calipers can measure external diameters, but they’re generally less precise and more prone to reading error for such tight tolerances. A dial indicator is used to check variations and runout relative to a reference, not to establish the exact diameter. A straight edge and feeler gauge set assess gaps, straightness, or fit, not the precise diameter of a journal.