28
VALVE CLEARANCE ADJUSTMENT
ALL O.S. four-stroke engines have their valve (tappet)
clearances correctly set before they leave the factory.
However, if, after many hours of running time have been
logged, a loss of power is detected, or if the engine has to
be disassembled or repaired as a result of an accident,
valve clearances should be checked and readjusted, as
necessary, with the aid of the O.S. Valve Adjusting Tool Kit.
Note:
Valve clearances of all O.S. four-stroke-cycle engines
must be checked and reset ONLY WHEN THE ENGINE IS
COLD. Procedure is as follows:
1. Remove all the glowplugs except the one installed in the
cylinder that you want to check.
2.
Note:
Each glowplug should be re-installed in to the original
cylinder. You may start to check and adjust with any
cylinder.
Turn the propeller counter-clockwise until compression is
first felt, then turn it futher a quarter turn. At this point, both
valves should be closed.
The standard valve clearance, on both inlet and exhaust
valves, is between 0.04mm and 0.1mm(0.0015-0.004 inch),
measured between valve stem and rocker arm. Use the
0.04mm and 0.1mm feeler gauges to check clearances.
(See Fig.1)
0.04mm
Feeler Gauge
Rocker Arm
Valve
3.
Note:
If the gap is found to be less than 0.04mm, it is not
necessary to readjust the clearance if the engine has
good compression and starts easily. Equally, if the gap
exceeds 0.1mm but is not more than 0.14mm (i.e. the
thickness of both feeler gauges inserted together), it is
not necessary to readjust the clearance if the engine
runs satisfactorily.
Fig.1
If a clearance is found to be outside either of these limits, it
should be reset as follows.
0.04m
m
29
Carefully loosen the locknut
on rocker-arm 1/4-1/2 turn
with 5mm wrench. (Fig.2)
1.
Loosen approx.1/4 to 1/2 turn.
Wrench
Locknut
2.Turn adjusting-screw approx.
1/2 turn counter-clockwise to
open gap, using appropriate
tool-i.e. Allen hex key. (Fig.3)
Adjusting
Screw
Allen Key
Turn approx.1/2 turn.
3.Insert 0.04mm feeler gauge
between valve stem and
rocker-arm and gently turn
adjusting screw clockwise
until it stops. (Fig.4)
0.04mm
Feeler Gauge
Turn with fingers
until it stops.
Remove 0.04mm feeler, recheck gap as explained in the
previous page.
5.
If clearance is correct, loosen the locknut on the other
rocker-arm and repeat steps 1 to 5 above.
6.
Remember:
Excessive valve clearance will cause loss of power, due
to valve (s) not opening sufficiently. On the other hand, a
total loss of clearance may cause difficult starting due to
valves not closing properly, resulting in loss of
compression.
Re-tighten locknut while holding adjusting screw stationary.
(Fig.5)
4.
Hold at the
screw head.
Tighten Locknut.
Fig.5
Fig.4
Fig.3
Fig.2
0.04m
m
0.04mm
Note:
The camshaft rotates one turn with every eight propeller
turns and has four projections on the profile. After
adjustment is completed, turn the propeller eight turns to
make sure you feel 4 times normal compression.
