F510 & F525 Cylinder Head and Valves – ANALYZE VALVES
Lead deposits on the intake valve are caused by exhaust gas leakage past the valve. This indicates that the valve is not seating properly.
IMPORTANT: Do not grind the exhaust valve or valve life will be shortened.
Grind intake valve and reface the seat to correct this condition.
NOTE: Be sure to reset valve-to-tappet clearance after grinding valves.
Valve stem corrosion is caused by moisture in the engine. Moisture in the fuel-air-mixture can condense inside the engine when the engine is stopped and cools down.
Valve corrosion can also occur during storage. Fogging or pouring oil in the combustion chamber before storing helps prevent valve corrosion.
Corroded or pitted valves collect deposits and may cause sticking valves. Replace badly corroded or pitted valves.
Exhaust valves are designed to function in temperatures exceeding (2760 ̊C) 5000 ̊F. However, when operating at high temperatures for long periods of time, valve burning may occur. Valves running too hot will show a dark discoloration of the valve stem into the area protected by the valve guide. Another indication is distortion of the valve margin (A) and valve face (B). Valve inserts may also begin to burn away.
IMPORTANT: DO NOT run the engine with blower housing removed.
Poor engine cooling due to dirt or obstructions is a common cause for overheating an engine and the valves. Remove blower housing and clean the engine cooling fins.
Other causes for valves running hot are worn valve guides or valve springs, incorrect valve clearance, lean fuel-air mixture and incorrect or overheated spark plug.
Using old or stale gasoline is a common cause for sticky valves (A).
This gummy deposit can be seen on the valve. When this condition exists, the carburetor may also contain gum deposits and will require a complete cleaning.
Always use fresh gasoline and drain fuel tank, lines, and carburetor before storing tractor.