Which surface is primarily involved in sealing against the seat?

Which surface is primarily involved in sealing against the seat?

• A. The valve stem
• B. The valve face
• C. The valve keeper
• D. The valve head

Answer: (B)

The sealing action happens at the contact between the valve face and the valve seat. When the valve closes, the face on the end of the valve presses against the seat in the cylinder head, forming a tight seal that stops combustion gases from leaking past. The stem and keeper mainly guide and retain the valve and don’t form the gas seal, while the head is the broader body of the valve and isn’t the sealing surface. For a proper seal, the valve face must mate correctly with a precisely machined seat; wear or damage can prevent a good seal and require reconditioning.

The sealing action happens at the contact between the valve face and the valve seat. When the valve closes, the face on the end of the valve presses against the seat in the cylinder head, forming a tight seal that stops combustion gases from leaking past. The stem and keeper mainly guide and retain the valve and don’t form the gas seal, while the head is the broader body of the valve and isn’t the sealing surface. For a proper seal, the valve face must mate correctly with a precisely machined seat; wear or damage can prevent a good seal and require reconditioning.