What Causes No Cylinder Compression in an Engine?

[DelRiver]

When a cylinder compresses, a certain pressure is generated inside it, which is called cylinder compression. No cylinder compression means the cylinder is not sealed, and pressure cannot be formed during compression. There are many reasons for no cylinder compression, such as valve breakage, cylinder scoring, cylinder gasket damage, etc. Below are detailed explanations: 1. Four-stroke engines: Mainly due to valve leakage, excessive clearance between the piston, piston rings, and cylinder block, cylinder gasket leakage, or the use of non-standard or mismatched parts like pistons, leading to reduced compression ratio and pressure drop. 2. Two-stroke engines: Primarily caused by wear of the cylinder block, piston, piston rings, crankshaft oil seal leakage, reed valve leakage, or cylinder gasket leakage.

[McIsabella]

I've repaired many engines with no cylinder compression, and the most common issue is problems with valve sealing, excessive valve clearance, or carbon buildup causing the valves not to close tightly. Worn or broken piston rings are also very common, especially in cars with poor oil quality, leading to cylinder leakage. Another common issue is a damaged cylinder head gasket, which often occurs after the engine overheats, and you can see bubbles in the radiator or emulsified oil. Once, I encountered a car where the timing belt skipped three teeth, directly bending the valves. The most troublesome issue is cylinder scoring, where the piston leaves deep marks on the cylinder wall—this requires replacing the engine block. Always measure the compression ratio first to confirm the problem before disassembling the engine blindly.

[Carson]

Last time my car wouldn't start due to insufficient cylinder pressure. The mechanic first asked if it was hard to start when cold, then had me listen to the starter sound, which indeed had abnormally fast RPM. The diagnosis showed valve leakage, and during repair, cracks were found in the valve seat. My friend's car had it worse - the piston rings were misaligned, allowing engine oil to enter the combustion chamber, resulting in blue exhaust smoke. Actually, spark plug thread leakage can also cause low cylinder pressure, especially in older cars with stripped threads. Some people even use the wrong oil viscosity, causing piston rings to seize. There are all kinds of potential issues. My advice is to check cylinder pressure as soon as starting difficulties appear, don't wait until engine shaking occurs to address it.

[LuciaMarie]

Insufficient cylinder compression is usually caused by issues in these areas: The valve system may be burnt or deformed, especially the exhaust valves which are prone to problems due to high temperatures; Worn piston rings can lead to excessive oil consumption and blue exhaust smoke; If the cylinder head gasket fails, coolant can enter the oil pan; Misaligned timing causing valve damage is the most troublesome issue. I've seen cases where air leakage occurred at the fuel injector mounting port due to loose screws. Damaged hydraulic lifters can also affect valve closure. For turbocharged vehicles, excessive intake pressure can damage piston rings. In short, all potential internal engine air leakage points must be checked. If the cylinder compression tester shows significant differences between the four cylinders, disassembly and inspection are definitely required.