by Chris Stevenson
moteur 2 image by thierry planche from Fotolia.com
The valve seats perform a very important function in the cylinder head, cooling rapidly to reduce the temperature and sealing the valve faces against flue gas leaks. The valve seats are of circular ring designs and are seated securely within the cylinder head through the use of a press. When the valve seat becomes worn, cracked, loose or damaged in any way, it can and should be removed. Valve seats can be removed with a variety of techniques and tools, depending on the valve head and seat material. The technician must implement the best removal technique for your valve seat system.
Place the cylinder head (or heads) upright on a hard surface. Use a carburetor and wire brush to thoroughly clean the surface of all carbon build-up, burn discoloration, oil, soot, and foreign debris. Rub the surfaces of the valve seat and the combustion chambers until they shine. Clean the outside of the head in the same way. Dry with a cloth. Use a magnifying glass to inspect all areas of the valve seat, combustion chamber roofs, and head contact surface for cracks or fine holes. Replace the head if there is any deformity.
Place the stock in a baking oven. Place the head with the combustion side down on the grate. Raise oven temperature to 450 degrees F. Let sit for 30 minutes or so. Open the door. Put on asbestos gloves and remove the rack from the oven. Turn your head, using long-handled channel locks. Check to see if any of the seats have come off and come loose. While the head remains warm, use an awl to pry the lips off the valves and loosen them.
Place the cylinder head in a large-jaw vise. Layer rags between the jaws and the head surface and tighten the vise. Place a fine, sharp chisel on the outer edge of the valve seat and strike the end of the chisel with a medium-sized hammer. Try playing in an upward and horizontal direction. Do not strike hard enough to drive the chisel into the cylinder head countersink. Many valve seats can be removed in this way.
Turn your head into a vise where the intake and exhaust ports face you. Shine a flashlight inside the ports and see if you can detect the edge of the valve seat lip. If you can see a lip, put a long drift punch on the end of the seat and hit the punch with a hammer. This method may work for some specific makes and models.
Use a die grinder and die grinder bit to machine the old seat, drilling slightly down over the valve seat, being careful not to grind past the seat and into the head. When the seat breaks loose and begins to rotate, use an awl or chisel to pry it out. This method works well on cast iron seats on aluminum heads.
Attach a cutting bit to a grinder that has dimensions slightly smaller than the width of the valve seat. Carefully cut the valve seat ring until it weakens. Do not cut the head material. Use a chisel or awl to pry out the seat.
- As an alternative method, if you are a skilled welder, you can weld a small bead around the outer perimeter of the valve seat. As the valve seat cools, it will contract and pop out. You can also insert a smaller used (junk) valve into the guide and weld the valve edges to the valve seat. Then take a hammer and hit the valve stem to pop the valve and seat together.
Articles will need
- Carb cleaner
- Wire brush
- Magnifying glass
- Bake oven (if applicable)
- Asbestos gloves
- Channel locks
- Scratch Awl
- Chisel (thin blade)
- Drift strike
- Grinder cutting bit