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    Valve Stem Seal

    Inspect/Replace/Store Service/Loan-a-tool

    Leaking valve guide seals account for nearly half of oil consumption complaints. A faulty intake seal allows oil to be drawn into the cylinder during the intake stroke.

    The atomizer effect results in oil being drawn down the exhaust guide as exhaust gas moving past the bottom of the valve guide creates a vacuum. Courtesy of Dana Corporation-Perfect Circle Division

    This results in burnt oil exhaust smoke when the engine decelerates because the oil is not being diluted with gasoline during that time. Under normal driving conditions, the air/fuel mixture would mix with the oil that leaked in, making it less visible. Next time you are driving down a long grade, notice how many cars in front of you have exhaust smoke. These are the ones that are using oil through the valve guides. Besides causing oil consumption, a leaking intake seal can result in carbon buildup on the stem of the valve (which interferes with engine breathing).

    Carbon buildup on the neck of the valve interferes with breathing.

    When an engine has relatively low mileage (under 60,000), the cause of internal oil consumption is often the valve guides. The car might smoke during deceleration (high engine vacuum) because of oil leaking into the combustion chamber through the intake valve guides. Smoke at other times might be from exhaust valve guides.

    When only one side of a spark plug is fouled with carbon, leaking guide seals are indicated. The carbon will be on the side of the spark plug that was facing the intake valve. Leaking valve guide seals also result in carbon deposits in the "neck" area of the intake valves.

    The atomizer effect results in oil being drawn down the exhaust guide as exhaust gas moving past the bottom of the valve guide creates a vacuum. Courtesy of Dana Corporation-Perfect Circle Division

    Watch for carbon deposits when disassembling a cylinder head.

    Valve seals come in three types: umbrella, positive, and O-ring.

    Three types of valve guide seals. Courtesy of Federal-Mogul Corporation

    An umbrella seal fits inside the valve spring. It fits the valve snugly and rides up and down with it, keeping oil from entering the valve guide. If an umbrella seal becomes brittle with age, it can become loose on the valve stem, which allows oil to leak down the valve guide. Sometimes umbrella seals break up, floating in the oil until the pieces are picked up by the oil pump. This can result in engine damage when the oil pump locks up.

    A valve guide and seal. Courtesy of Federal-Mogul Corporation

    A positive valve seal fits on the top of the valve guide. The valve moves up and down inside of a positive valve guide seal. Positive seals are used on overhead cam engines because the camshaft is heavily lubricated right above the valves. Occasionally, positive seals are also used on pushrod engines.

    A positive valve seal fits snugly on the valve guide. Courtesy of Mercedes-Benz of North America, Inc.

    An O-ring seal is the type used by General Motors. It fits under the keepers, inside of the spring retainer. Oil is pumped through the pushrod to a hole in the rocker arm and spills onto the retainer. Without the O-ring seal, oil would be able to leak down the stem and into the guide.

    • When the valve cover is removed, the standard umbrella guide seal can be checked to see if it has become brittle.
    • Insert a pocket steel rule between the coils of the valve spring, and push on the seal to see if it is still soft.
    • The seal should also be checked to see that it still fits the valve stem tightly.
    • Valve guide seals are replaced during a valve job while the heads are disassembled.

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