O.S. Engines FS-52S - Manual (Page 19)

• Feeler gauge 0.04mm
The kit comes in a plastic case and includes:
(Code No.72200060)
• 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:
Remove the cover from the rocker-box on top of the
cylinderhead, using the correct size Allen hex key. 1.
( 1 )
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.) 2.
The standard valve clearance, on both inlet and
exhaust valves, is between 0.04mm and
0.10mm(0.0015-0.004 inch), measured between
valve stem and rocker arm. Use the 0.04mm and
0.10mm feeler gauges to check clearances.
(See Fig.1.) 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 0.10mm 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
0.04mm
Feeler Gauge
Rocker Arm
Valve
18