Valve seats perform a very important function on the cylinder head, cooling rapidly to reduce temperature, and sealing the valve faces against combustion gas leakage. Valve seats have circular ring designs, and sit fixed within the cylinder head, by 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 upon the valve seat and head material. The repair person should implement the best removal technique for his valve seat system.
- Skill level:
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Things you need
- Carburettor cleaner
- Wire brush
- Magnifying glass
- Bake oven (if applicable)
- Asbestos gloves
- Channel locks
- Scratch awl
- Bench vice
- Chisel (thin blade)
- Flash light
- Drift punch
- Die grinder
- Die grinder cutting bit
Face the cylinder head (or heads) face up on a hard surface. Use carburettor and a wire brush to thoroughly clean the surface of all carbon build-up, scorch discolouration, oil, soot and foreign debris. Scrub the valve seat surfaces and combustion chambers until shiny. Clean the outside of the head in the same fashion. Wipe dry with a rag. Use a magnifying glass to inspect all valve seat areas, combustion chamber roofs and head mating surface for hairline cracks or holes. Replace the head if any deformities exist.
Place the cylinder head inside a bake oven. Position the head with the combustion side down on the grille rack. Raise the oven temperature to 232 degrees C. Let it set for 30 minutes or so. Open the door. Don asbestos gloves and pull the oven rack out. Flip the head over, using long-handle channel locks. Notice if any of the seats have dislodged and fallen free. While the head remains hot, use a scratch awl to pry the lips on the valves and break them loose.
Place the cylinder head in a large-jaw bench vice. Place layers of rags between the jaws and the head surface and tighten the vice. Place a sharp, thin chisel in the outermost lip of the valve seat and tap the end of the chisel with a medium-size hammer. Try to tap in an upward direction, as well as horizontally. Do not strike hard enough to drive the chisel into the cylinder head counter bore. Many valve seats can be removed this way.
Turn the head over in a vice where the intake and exhaust ports face you. Shine a flashlight down inside the ports and see if you can spot the edge of the valve seat lip. If you can see a lip, place a long drift punch on the end of the seat and tap the punch with a hammer. This method can work on some certain make and model heads.
Use a die grinder and die grinder bit to machine the old seat out, by drilling lightly down over the valve seat, being careful not to grind past the seat and into the head. When the seat breaks lose and begins rotating, use a scratch awl or chisel to pick it out. This method works well on cast iron seats in aluminium heads.
Attach a cutting bit on a die grinder that has dimensions slightly smaller than the valve seat width. Carefully cut into the valve seat ring until it weakens. Do not cut into the head material. Use a chisel or scratch awl to pry the seat out.
Tips and warnings
- As an alternate method, if you are a skilled welder you can weld a small bead around the outside 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 edges of the valve to the valve seat. Then take a hammer and hit the valve stem to pop the valve and seat out together.
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