Leaking Valve Seals

Blue/Gray Exhaust: Leaking Valve Seals

Leaking valve seals result in blue-gray exhaust. This smoke is caused by engine oil leaking past the seals, into the combustion chamber. These seals allow the valves to move up and down, while providing a thin film of oil for lubrication. Valve stems ride in valve guides; the seal contains and controls the amount oil used to lubricate the moving stem. Here are three types of seals found today. The most popular of these is the positive valve seal.

Positive valve seals: These seals are rubber or plastic, and snap into place in a groove machined into the cylinder head. They sometimes require a special tool or a 10mm socket to install. The intake and exhaust seals can be distinguished apart because they’re different sizes and colors.

Umbrella valve seal: Umbrella valve seals used to be everywhere. They were used on all different kinds of engines. These seals are installed after the valve has been placed in its guide. Polish the valve with crocus cloth and lubricate it with oil or assembly lube before installation.

O-rings: O-rings are installed on the valve stem. They are installed after the valve spring has been compressed on the third groove down. Lubricate the seal with oil before sliding it over the valve stem. Check the manufacturer’s manual for any special procedures.