ASE A1 Engine RepairEngine Block AssemblyMedium
A technician is inspecting the main bearing caps after removal. Which of the following is an indication that a main bearing cap has been 'walked' or improperly torqued?
- AA slight increase in bearing clearance measured with Plastigage.
- BConsistent oil film residue across the entire bearing surface.
- CUniform, shiny wear on the bearing shell surface.
- DScuffing or fretting on the mating surfaces between the cap and the block.
Show answer & explanationAnswer & explanation
Correct answer: D. Scuffing or fretting on the mating surfaces between the cap and the block.
Scuffing or fretting on the mating surfaces between the main bearing cap and the engine block indicates movement or improper seating of the cap, often due to incorrect torque procedures or a 'walking' cap, which can lead to bearing failure.
Why the other options are wrong
- A. A slight increase in bearing clearance might indicate wear, but not specifically cap 'walking'.
- B. Consistent oil film residue is normal and indicates proper lubrication.
- C. Uniform, shiny wear indicates normal operation and proper lubrication.
Main Bearing Cap 'Walking'
A condition where a main bearing cap shifts or moves slightly relative to the engine block due to insufficient or uneven torque, causing fretting, wear, and potential bearing failure.
- Caused by improper torqueing procedures or loose bolts.
- Identified by fretting or scuffing marks on the cap-to-block mating surfaces.
- Leads to loss of bearing crush, reduced oil pressure, and accelerated bearing wear.
Memory trick: Cap moves, surfaces rub, a walk can lead to a costly hub.