TM 5-3805-281-24-2
Cylinder Head and Valves
CHECK AND ADJUST VALVE CLEARANCE
Too little valve clearance throws valves out of time.
Valves open too early and close too late. This causes the
valves to overheat due to hot combustion gases rushing
past valves when out of time. Overheating lengthens valve
stems which prevents proper seating of valves. The
valves seat so briefly or poorly that normal heat transfer
into the cooling system does not have time to take place,
causing burned valves and low power.
Too much valve clearance causes a lag in valve timing
causing engine valve train imbalance. The fuel-air mixture
Flywheel Turning Tool and Timing Pin
enters the cylinders late during intake stroke. The exhaust
valve closes early and prevents waste gases from being
completely removed from cylinders. Also, the valves close
with a great deal of impact, which may crack or break the
valves and scuff the camshaft and followers.
IMPORTANT: Valve clearance MUST BE checked and
adjusted with engine COLD.
IMPORTANT: Visually inspect contact surfaces of
wear caps and rocker arm wear pads.
Check all parts for excessive wear,
breakage, or cracks. Replace parts that
show visible damage.
1. Remove rocker arm cover with ventilator tube.
2. Remove plastic plug from cylinder block bores and
install JDE81-1 or JDG820 Flywheel Turning Tool (A)
and JDE81-4 Timing Pin (B).
3. Rotate engine with the flywheel turning tool until timing
pin engages timing hole in flywheel.
If the rocker arms for No. 1 cylinder are loose, the
engine is at No. 1 "TDC-Compression."
If the rocker arms for No. 6 cylinder are loose, the
engine is at No. 6 "TDC-Compression." Rotate the
engine one full revolution to No. 1 "TDC-Compression."
Continued on next page
RG,RG34710,1069
1923OCT971/2
