uniform. Temperature changes affect air-cooled
engines to a greater extent than other engines, and there
must be sufficient valve clearance to prevent valve from
holding open when extreme cold is encountered, since
holding open will make cold weather starting extremely
difficult. Inadequate clearance or excessive clearance is
conducive to valve failure; therefore, proper settings are
essential to engine operation.
clearance When rough engine operation, backfiring, loss
of compression, hard starting, or any malfunction which
can be attributed to improper operation or clearance of
valves occurs, valve clearance shall be measured and
adjusted, using the following procedures
contained In applicable engine maintenance manual.
Locate top dead center piston
Use feeler gauge (shaped so that
end of gauge can be slipped in a straight line between
valve and rocker arm roller or adjusting screw) specified
in tools section of maintenance manual.
Do not use excessive force to insert
adjustment screw or rocker arm roller.
Adjust valve clearances found to be
out of adjustment according to specific procedures in
engine maintenance manual.
sodium-filled valves. The reclamation procedure for
sodium-filled valves consists primarily of rebuilding the
facing of exhaust valves and repairing the stems
Do not attempt to mutilate sodium-
filled valves. The metallic sodium
contracting moisture, gives off highly
flammable hydrogen gas, and when
brought into contact with the skin
often results in severe personal injury.
determined to be nonrepairable as a result of cracked or
broken stems shall be processed for disposition In
accordance with procedures established by Part 3,
Chapter XV, DOD directive 4160 21M. Disposal of these
nonrepairable valves shall be affected by one of the
Burial, at least 30 inches below ground level, in
a select location where future excavation is
By dumping at sea.
Values determined to be suitable
for reclamation shall be prepared for shipment in
accordance with provisions of AR 746-1.
Establishing crankshaft position using
top center indicator and protractor. The proper crankshaft
position must be established prior to checking or setting
valves using the following procedures.
indicator, as shown in figure 7-15, pointer travel to
Install Indicator in either spark plug
hole of number one cylinder.
Adjust arm of indicator so that full
scale deflections will be obtained as piston moves through
its full stroke.
specified in engine maintenance manual on one of engine
accessory drive pads.
direction of rotation until piston is coming up on
Figure 7-15. Top Center Indicator