The cause of the valve leak on the factory stock motorcycle

The issue of a leaking valve in a motorcycle engine can cause the bike to lose power or even prevent it from starting altogether. The valve leak occurs due to various factors. One common cause of motorcycle valve leakage is the accumulation of carbon deposits in the combustion chamber.

Thick carbon deposits build up on the piston surface and within the combustion chamber over time, gradually spreading toward the valve seat.

The valve fails to close tightly due to the carbon buildup on the valve seat. This is where the leakage problem arises. The valve can also become damaged or bent due to carbon deposits.

Need More Information? Check out our top posts:

motorcycle valves leak carbon

Bent Valve

A bent valve can also be caused by the thick deposits above the piston head. These deposits mound up and cover the valve pocket on the piston, eventually leading to a collision that results in valve bending.

For factory stock engines, this issue takes a while to develop, but it can easily occur in modified engines or due to errors during the repair process.

Signs of a bent valve include engine sputtering and easy stalling. In severe cases, the engine won’t start at all.

Broken Valve

While rare in factory stock motorcycles, this issue is more common in modified engines. It occurs due to piston “clashes,” timing chain breakage, or valve burning due to incorrect engine tuning. The consequences lead to damage to all components within the cylinder block and head.


In most cases, valve leaks stem from low-quality engine oil that quickly produces carbon deposits. Owners should diligently adhere to the motorcycle service schedule established by the manufacturer.

Leave a Comment

Alamat e-mel anda tidak akan disiarkan. Medan diperlukan ditanda dengan *

Scroll to Top