What does the term 'out-of-round' describe in crankshaft journals?

• A. It is a deviation from a perfect circular cross-section
• B. It is the diameter
• C. It is the length
• D. It is the surface finish

Answer: (A)

Out-of-round means the journal’s cross-section isn’t a perfect circle; it’s oval or otherwise noncircular. In a properly machined crankshaft, the bearing surface stays the same size all the way around as the crank rotates, so the oil film and clearance stay consistent. When the journal is out-of-round, the diameter varies as you go around the circumference, causing the bearing clearance and oil film to change during rotation. That leads to uneven wear, vibrations, and potential bearing problems. This is a geometric deviation from circular shape, not simply a different diameter, length, or surface finish.