How to Replace Valve Stem Oil Seals

by Teeter Allen Morrison

The advent of the overhead valve engine brought with it several problems. One such problem was that when the intake valve opened, the piston would draw oil down the valve stem into the cylinder. The oil would mix with the air and fuel and burn. The engine would then smoke, causing it to consume oil. Valve seals are used to block the direct draw down the valve's stem. Some seals look like little umbrellas with holes in them, while some are just little O-rings that slide over the stem.

Disconnect the negative battery cable from the battery.

Remove the spark plugs from the engine, using the spark plug wrench. Mark the spark plug wires so they can be easily reconnected to their respected spark plug during reassembling.

Remove the valve covers using a small socket and ratchet. Slowly rotate the engine by hand in the same direction as it runs, while someone your assistant holds his finger over the number one spark plug hole until compression is felt. When compression is felt, bring the zero line on the harmonic balancer within an inch of aligning the timing mark on the engine.

Cut a strip of paper one inch wide. Wrap the paper around the harmonic balancer and mark it so it can be cut the exact same circumference as the balancer. Measure the strip of paper, then divide the measurement by the number of cylinders in the engine. Mark those graduations on the paper. If the engine is a four cylinder, just fold the paper twice and mark the folds as graduations. If the engine is an eight cylinder, fold the paper four times and mark the folds. Tape the paper to the harmonic balancer with the two ends of the paper at the zero line on the balancer.

Push all but two inches of the 1/4-inch nylon rope into the cylinder. Rotate the engine by hand until the rope inside the cylinder is wedged between the piston and valves. The nylon rope keeps the valves from dropping into the cylinder.

Remove the rocker arms from the valves on cylinder number one. Count the exact number of turns on the rocker arm nuts and record the numbers for easy replacement. Clamp the valve spring compressor on top of the valve spring washer and compress the spring. Push down on the compressor and carefully remove the split valve keepers. Take great care not drop the valve keepers into the engine. Remove the valve spring. Pull the old seal off the valve stem and replace it with a new valve seal.

Place the valve spring that's still in the spring compressor back onto the valve stem. Place the two split valve keepers into the tapered valve spring washer. Pull up the valve spring compressor to force the washer to seat the split valve keepers. Slowly loosen the valve compressor until the spring is supported between the valve keepers and the cylinder head. Repeat this step with the other valve on this cylinder so both valves seals are replaced. Reinstall the rocker arms and adjuster nuts.

Back up the engine enough to remove the nylon rope from the cylinder. After removing the rope, rotate the engine by hand in the same direction that the engine runs, until the timing pointer is within an inch of the next alignment mark on the paper taped to the balancer. Consult the service manual for the firing order of your specific engine and push all but two inches of the nylon rope into the cylinder that follows cylinder number one. Rotate the engine until the rope is wedged between the piston and both valves and repeat steps 6 and 7. Follow this procedure until all the valve seals are replaced.

Check the valve cover gasket for damage. If gasket are damaged replace them. Reinstall the valve covers onto the cylinder heads and tighten. Reinstall the spark plugs and plug wires onto the proper spark plugs. Replace the negative battery terminal.

Tips

  • check Apply light oil to the valve seals prior to installation.
  • check Be sure there is enough rope to fill the cylinder to hold up both valves.
  • check Insert shop rags into the oil holes into the head to prevent anything from falling in them.
  • check Consult the service manual for the cylinder numbers and firing order.

Warnings

  • close Always wear eye protection when working on or around automobiles.
  • close Oil is a known irritant avoid contact with skin or eyes.

Items you will need

About the Author

Teeter Allen Morrison has been writing for more than 20 years. His work has appeared in Peterson Publishing's "Stock Car" magazine's Technical section and he has authored some popular articles for various websites. In earlier years Morrison accepted an engineer apprenticeship with the Local Iron Workers Union. He is a graduate of Writer's Digest University.

Photo Credits

  • photo_camera mécanisme à explosion image by rachid amrous-spleen from Fotolia.com