ASE A1 Engine RepairLubrication and Cooling SystemsHard
A vehicle is brought into the shop with a complaint of a grinding noise coming from the engine, especially noticeable at higher RPMs. The technician also observes metal particles in the oil filter during an oil change. Oil pressure is within specification at idle, but drops slightly at higher RPMs. Which of the following is the MOST likely cause?
- AWorn main or rod bearings
- BA failing oil pump relief valve
- CA collapsed hydraulic lifter
- DWorn camshaft lobes
Show answer & explanationAnswer & explanation
Correct answer: A. Worn main or rod bearings
Grinding noises, especially at higher RPMs, accompanied by metal particles in the oil and a slight drop in oil pressure at higher RPMs, are strong indicators of worn main or rod bearings. The grinding is from metal-on-metal contact, and the metal particles are evidence of this wear. Worn bearings increase clearances, leading to a slight pressure drop when the pump works harder at higher RPMs.
Why the other options are wrong
- B. A failing oil pump relief valve could cause either excessively high or low oil pressure, but not necessarily grinding and metal particles unless it led to severe bearing failure.
- C. A collapsed hydraulic lifter causes a ticking noise, not grinding, and wouldn't produce significant metal particles in the oil filter.
- D. Worn camshaft lobes would cause ticking or tapping, and engine performance issues, but not typically a grinding noise or significant metal particles in oil.
Engine Bearings (Main & Rod)
Sacrificial components that provide a low-friction surface for rotating crankshaft and connecting rods, separating them from fixed engine components with a film of oil.
- Made of softer metals (e.g., Babbitt, copper, lead alloys).
- Wear over time, increasing clearance and reducing oil pressure.
- Failure can lead to knocking/grinding noises and catastrophic engine damage.
Memory trick: Grinding metal, pressure fallin', bearings are callin'!