1. Check for carbon deposits, a bent valve guide, defective spring, or antifreeze (glycol) in the
lubricating oil. Replace a bent guide. Clean up and reface the valve. Replace the valve if necessary.
2. Check for excessive valve-toguide clearance, bent valve guide, or carbon deposits. Replace a bent
or worn guide. Clean the carbon from the valve. Reface or replace the valve, if necessary.
3. Check the operating conditions of the engine for overload, inadequate cooling, or improper
timing. Reface the valve and insert. Replace the valve if it is warped or too badly pitted. Use a harder-face
valve if operating conditions warrant.
4. Check for contact between the valve head and the piston as a result of incorrect valve clearance, an
improperly positioned exhaust valve bridge (four-valve head), or a defective spring. Check the valve guide,
insert, cylinder head, and piston for damage. Replace damaged parts.
5. Check for excessive valve-toguide clearance, defective valve spring or etching of the valve stem at
the weld. Improper valve clearance is also a cause of this type of failure. Check the guide, insert, cylinder
head, and piston for damage. Replace damaged parts.
6. Replace a worn valve guide. Check and replace the valve, if necessary.
7. Black carbon deposits extending from the valve seats to the guides indicates cold operation due to
light loads or to the use of too heavy a fuel. Rusty brown valve heads with carbon deposits forming narrow
collars near the guides indicate hot operation due to overloads, inadequate cooling, or improper timing which
results in carbonization of the lubricating oil. Clean up the valves, guides, and inserts. Reface the valves and
inserts or replace them if they are warped, pitted, or scored.
8. Check for worn valve guide or excessive exhaust back pressure. Replace a worn guide. Check the
valve seat for improper seating. Reface the valve and insert or, if necessary, replace.
9. Check for a bent valve stem or guide,. metal chips or dirt, or for lack of lubrication. Clean up the
valve stem with a crocus cloth wet with fuel oil or replace the valve. Replace the guide. When installing a
valve, use care in depressing the spring so that the spring cap DOES NOT scrape the valve stem.
10. Check for a gear train failure or for improper gear train timing.
11. Check the operation of the engine for excessive idling and resultant low-engine exhaust back
pressure. Install valve guide oil seals.