What is Valve Seat Recession?
Valve Seat Recession (VSR) is the tendency for the valve seat sealing face to shrink upwards into the cylinder head. When this occurs, the valve will be pulled further up into the cylinder head to meet the shrunken (recessed) valve seat by the powerful springs which are used to close it. Eventually, the point is reached where the valve head and stem have moved up so far that the top of the valve stem is touching the cam follower, tappet or whatever for all of the time. There should be a clearance gap here which normally ensures full and correct sealing of the valve. If there is no clearance gap, the valve may be held slightly open by the contact with the cam follower or tappet. If this happens the cylinder involved cannot be truly gas tight. The condition may result in the affected cylinder producing far less than its normal power or produce no power at all. This is because the affected cylinder will have low (or no) compression due to the leakage at the valve. What are the causes of V
