ASE A1 Engine RepairEngine Block AssemblyHard
A technician is inspecting a crankshaft for potential reuse. They use a micrometer to measure the main journal diameter at several points around its circumference and along its length. Which of the following conditions would indicate that the journal needs to be reground or replaced?
- AThe journal has a consistent taper of 0.0002 inches along its length.
- BThe journal surface is perfectly smooth and shiny, without any visible cross-hatch.
- CThe journal diameter is consistently 0.0005 inches larger than specification.
- DThe journal shows signs of being 'out-of-round' by 0.001 inches.
Show answer & explanationAnswer & explanation
Correct answer: D. The journal shows signs of being 'out-of-round' by 0.001 inches.
Out-of-roundness on a crankshaft journal means it is no longer perfectly circular, which will prevent a uniform oil film from forming and lead to premature bearing wear and potential engine damage. A deviation of 0.001 inches is significant enough to require correction.
Why the other options are wrong
- A. A consistent taper of 0.0002 inches is generally within acceptable manufacturing tolerances for many journals or can be corrected with minor polishing, especially if it's very slight.
- B. A perfectly smooth and shiny journal indicates excessive wear and lack of oil retention, but the question asks for a condition that specifically requires regrinding, and out-of-roundness is a direct geometric defect requiring machining.
- C. A journal being consistently slightly larger might indicate an incorrect measurement or a previous machining error, but uniform oversize doesn't inherently cause operational issues as much as out-of-roundness.
Crankshaft Journal Out-of-Round
A condition where a crankshaft journal is no longer perfectly circular, leading to uneven bearing loading, compromised oil film, and accelerated wear.
- Measured with a micrometer
- Causes uneven oil film and bearing contact
- Requires regrinding or replacement if exceeding specifications
Memory trick: Roundness lost, bearing costs.