* Low oil pressure: Insufficient lubrication allows engine components to rub against each other, creating a knocking sound. This could be due to low oil level, a failing oil pump, or a clogged oil filter.
* Worn connecting rod bearings: These bearings support the crankshaft and if worn, will cause a knocking sound, especially noticeable under load.
* Worn piston rings: Worn piston rings allow combustion pressure to escape into the crankcase, leading to a knocking or pinging sound.
* Damaged crankshaft: A bent or damaged crankshaft can cause a significant knocking sound.
* Valvetrain issues: Worn or damaged rocker arms, lifters, or pushrods can produce knocking.
* Rod knock: This is a severe condition where the connecting rod bearings are completely worn, causing a loud and unmistakable knocking noise. This usually requires immediate engine repair or replacement.
* Insufficient octane fuel: In older engines, using fuel with a lower octane rating than recommended can cause detonation (pinging or knocking) due to premature ignition.
* Loose or broken timing chain/belt: While less common to sound specifically like a knock, issues with timing components can cause abnormal engine noises that might be confused for a knock.
Without physically inspecting the engine, it's impossible to say definitively what's causing the knock. A mechanic would need to diagnose the problem.
