Valve Guide Seal: Service Precautions

CAUTION
In Vehicle Valve Stem Seal Replacement
Failure of air pressure to hold the exhaust valve and intake valve closed while replaceing the valve stem seal is an indication of valve and/or valve seat damage and requires removal of cylinder head. If Air pressure fails during valve stem seal replacement, and the piston is not at top dead center, the valve will fall into the cylinder and will require cylinder head removal.