What can cause valve sticking in an engine?

Gum and varnish buildup is a significant factor in causing valve sticking in an engine. This buildup typically occurs due to the oxidation of oil and the combustion of fuel, leading to deposits forming on the engine components, including valves. When these deposits accumulate, they can restrict the free movement of the valves or their guides, preventing them from opening and closing properly. This can lead to performance issues, such as reduced engine power, misfires, or engine knocking.

While lack of lubrication, cold temperatures, and excessive oil consumption can contribute to overall engine wear or other issues, they do not directly cause the sticky condition of the valves in the same way that gum and varnish do. Proper maintenance, including regular oil changes and using high-quality lubricants, can help mitigate these deposit formations, ensuring smooth valve operation.