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23
VALVE CLEARANCE ADJUSTMENT
Remove the rocker cover from each cylinder head by
unscrewing two socket-head cap-screws from the rocker
box on top of the cylinder head with Allen key supplied.
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.
Feeler gauge 0.04mm
The kit comes in a plastic case and includes:
Feeler gauge 0.1mm
Hex. key 1.5mm
Wrench 5mm
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 fitted to the
cylinder that you want to check.
2.
Note:
Each glowplug should be re-fitted 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 quarter turn. At this point, both
valves should be closed. (If the prop driver ('drive hub') of
your engine is engraved with a letter 'T', this mark should
now be at the top.)
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.29.)
Fig.29
0.04mm Feeler Gauge
Rocker Arm
Valve
3.
4.
24
If a clearance is found to be outside either of these limits, it
should be reset as follows.
Carefully loosen the locknut on rocker-arm 1/4-1/2 turn with
5mm wrench. (Fig.30.)
1.
Fig.30
Slacken 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.31.)
Fig.31
Adjusting Screw
Allen Key
Turn approx.1/2 turn.
3.
Fig.32
Insert 0.04mm feeler gauge between valve stem and rocker-
arm and gently turn adjusting screw clockwise until it stops.
(Fig.32.)
0.04mm Feeler Gauge
Turn with fingers until it stops.
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.