O.S. Engines FS-52S - Manual (Page 20)

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.2.) 1.
2.
3.
Wrench
Slacken approx.
1/4 to 1/2 turn.
Turn adjusting-screw approx. 1/2 turn counter-clockwise
to open gap, using appropriate tool -i.e. Allen hex key.
(Fig.3.)
Fig.2
Fig.3
Fig.4
Adjusting
Screw
Turn approx.
1/2 turn.
Allen Key
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.
Locknut
Re-tighten locknut while holding adjusting screw
stationary. (Fig.5.) 4.
Hold at the screw head.
Fig.5
Tighten Locknut.
19
( 2 )