ASE A1 Engine RepairEngine Block AssemblyEasy
A technician is preparing to install a crankshaft into an engine block. Before final assembly, what critical measurement must be taken to ensure proper oil film formation and prevent premature bearing failure?
- AMain bearing oil clearance.
- BConnecting rod side clearance.
- CCrankshaft journal runout.
- DCrankshaft end play.
Show answer & explanationAnswer & explanation
Correct answer: A. Main bearing oil clearance.
Main bearing oil clearance is the critical measurement that directly ensures proper oil film formation between the crankshaft journals and the main bearings. Incorrect clearance (too tight or too loose) will lead to lubrication issues and premature bearing failure.
Why the other options are wrong
- B. Connecting rod side clearance ensures proper movement of the connecting rods on the crankshaft, not main bearing lubrication.
- C. Crankshaft journal runout affects bearing wear but is not the direct measure of oil film space.
- D. Crankshaft end play is important for preventing thrust bearing wear and crankshaft movement, but not for main bearing oil film.
Main Bearing Oil Clearance
Main bearing oil clearance is the precise gap between the crankshaft main journals and the main bearings, essential for establishing a hydrodynamic oil film.
- Too little clearance restricts oil flow, causing overheating and metal-to-metal contact.
- Too much clearance reduces oil pressure and allows excessive oil leakage, leading to bearing wear.
- Measured using Plastigage or a dial bore gauge with a micrometer.
Memory trick: Oil clearance is the 'clear' path to lubrication.