NOCTI Diesel Technology Practice Test

Journals on a crankshaft must maintain precise size and shape to ensure the bearings ride smoothly and the oil film is consistent. Besides diameter and how much the journal deviates from a perfect circle (out-of-round), the other important dimensional characteristic is taper—the change in diameter along the length of the journal.

Measuring taper involves taking diameter readings at both ends and in the middle (and sometimes along intermediate points) and comparing them. If the diameter differs from one end to the other beyond spec, the bearing clearance will not be uniform, leading to uneven wear, reduced oil film stability, and potential bearing failure. Use a micrometer or a bore gauge setup to check these points, ensuring the readings stay within the specified tolerance.

Temperature and vibration describe operating conditions, not the geometric size or shape, and the other options (length, width, height) don’t pertain to journal geometry.