Valve is sticking.
Cause
There are deposits on valve stem. Worn valve guide. Warped valve stem. There is insufficient oil. The valves are overheating.
Solution
Clean or remove the deposits. Replace the valve. Check the oil, service the lubricating system.
Problem
Valve burning.
Cause
Valve is sticking. The valve seat id distorted. The valve tappet clearance is too small. Spring cocked or weak. The engine is overheated. Lean air fuel mixture. Pre ignition problem. Detonation problem. The valve seat has leakage. Loose valve guide.
Solution
Check cooling system and tighten the cylinder head bolts. Adjust the valve tappet clearance. Replace spring. Check cooling system. Service fuel system. Clean carbon from engine and use cooler plugs. Adjust the ignition timing and use higher octane fuel. Relap valve face and seat. Replace valve guide.
Problem
Valve breakage.
Cause
The valve is burning. Detonation problem. Excessive valve tappet clearance. The valve is sticking. There are scratches on valve stem.
Solution
Adjust the ignition timing and use higher octane fuel. Adjust valve tappet clearance. Replace valve.
Problem
Valve face wear.
Cause
Excessive valve tappet clearance. Dirt on face valve.
Solution
Adjust the valve tappet clearance. Clean and check air cleaner.
Problem
Valve deposits.
Cause
There is carbon from rich mixture. The valve guides are worn. There is carbon from poor combustion. Used of dirty and wrong oil.
Solution
Service fuel system. Replace worn valve guides. Service fuel system, ignition or service engine. Replace oil.
