ASE A1 Engine RepairEngine Block AssemblyHard
A technician is preparing to install a new crankshaft into an engine block. Before installing the main bearings, what critical measurement must be taken to ensure proper bearing crush and prevent bearing spinning?
- AMain bearing shell thickness.
- BMain bearing housing bore out-of-round.
- CCrankshaft journal diameter.
- DMain bearing housing bore diameter.
Show answer & explanationAnswer & explanation
Correct answer: D. Main bearing housing bore diameter.
The main bearing housing bore diameter is a critical measurement. If this bore is too large or out-of-round, the bearing shells will not have sufficient 'crush' when the caps are torqued, leading to bearing spinning, overheating, and failure.
Why the other options are wrong
- A. Main bearing shell thickness is a manufacturing specification and is not typically measured by the technician to determine crush directly; it's used with bore and journal to find clearance.
- B. While out-of-round is important, the diameter itself is the primary measurement to ensure correct bearing crush when new bearings are installed.
- C. Crankshaft journal diameter is measured to determine proper bearing clearance, but not bearing crush.
Main Bearing Housing Bore Measurement
Measuring the main bearing housing bore diameter is crucial to ensure correct bearing crush and prevent bearing spinning during engine assembly.
- Must be perfectly round and within specification.
- Determines how tightly the bearing shells are held.
- Incorrect size leads to bearing failure.
Memory trick: Bore diameter correct, bearing crush perfect.