What are the reasons for no cylinder compression after overhauling BMW N46 engine?

[OHazel]

BMW N46 engine has no cylinder compression after overhaul due to the following reasons: Severe wear of piston rings leading to reduced sealing effectiveness: There are three piston rings: two compression rings and one oil ring. The compression rings prevent the mixture from entering the crankcase, while the oil ring primarily serves a lubricating function, reducing wear on the cylinder walls and piston rings. Scratched and uneven abnormal wear on cylinder walls: Carbon deposits or other foreign particles enter the cylinder and scrape against the cylinder walls during piston movement, causing scratches. Poor sealing of valve seats and spark plug seats: Excessive torque during spark plug installation damages the threads. Carbon deposits cause poor sealing of valve seats, as carbon adheres to the valves, preventing them from closing properly against the valve seats, resulting in insufficient cylinder compression and air leakage.

[StWilliam]

I've seen quite a few cases of N46 engines having no cylinder pressure after overhaul. The most common issue is valve-related - either improper valve clearance adjustment during repair or leaking valves themselves. Especially with precision engines like BMW's, even minor mistakes can lead to compression loss. Piston rings are another pitfall; if installed incorrectly with stuck rings or misalignment against cylinder walls, pressure won't build up. Incorrect timing chain installation is more troublesome - any misalignment disrupts valve timing and significantly reduces compression. The cylinder head gasket is also critical; poor sealing causes inter-cylinder leakage. I've handled similar cases in the workshop where assembly carelessness was immediately apparent. I recommend visiting a professional shop for compression testing immediately - DIY attempts might worsen the problem. Engine health affects driving safety, and timely diagnosis can save significant costs.

[KaiLee]

Oh, I remember my friend's BMW also had no cylinder pressure after a major overhaul. It turned out the valves weren't installed properly, probably due to careless adjustment during repairs. Piston ring issues are common too - if rings are installed backwards or damaged, they can easily get stuck. If the timing chain is wrong, compression will instantly drop to zero. Mechanics must align the timing marks when installing the chain. Valve leakage or cylinder gasket failure isn't surprising either - uneven application of sealant during assembly can cause this. My advice: check valves and rings first, then test the timing system. If all else fails, send it for professional repair. Don't delay, to avoid accidents on the road. Safety first, my friend.

[LeCamilla]

Buddy, I've been into cars for years and encountered this issue when working on BMW N46 engines. No cylinder compression is usually due to assembly flaws: poor valve sealing, incorrect valve clearance; piston rings installed incorrectly, causing cylinder leakage; timing chain misalignment leading to incorrect valve timing; or deformed cylinder gasket causing air leaks. A compression test can quickly pinpoint the problem. Early diagnosis helps avoid more severe damage, like engine failure.