What is the most common cause of engine valve sticking?

The most common cause of engine valve sticking is resinous deposits from improper lube oil or fuel. Engine components, particularly valves, are exposed to high temperatures and pressures, which can lead to the formation of deposits if the oil or fuel is not of adequate quality. Low-quality lubricants or fuels can degrade under operating conditions, resulting in the buildup of carbon or varnish-like materials on the valves and valve guides. These deposits can create friction, preventing the valves from moving freely and causing them to stick.

Proper maintenance of the engine, including the use of high-quality lubricants and fuels, is crucial to minimize the accumulation of these harmful deposits. Maintaining the correct operating temperatures and ensuring that the engine is regularly serviced can also help. Understanding this can aid in troubleshooting and preventing valve-related issues in an engine.