Ignition Timing; Instructions For Setting Tappets; Magneto Pinion Extractor - BSA M20 Maintenance Manual And Instruction Book

Fig. 8. Instructions for setting tappets
The actual adjustment is carried out by releasing the
locknut (B) (Fig. 8), holding the tappet with a spanner
on the flat (C), and screwing the tappet head (A)
either up or down. When correct clearance is
obtained, the locknut must be tightened against the
tappet head. It is advisable, after locking up, to
check clearance again, to make sure that the
adjustment has not been affected.
Tappet adjustment should always be carried out with
the engine dead cold, and the clearances
recommended above regarded as a minimum,
especially in the case of the exhaust valve.

IGNITION TIMING

It is a rare occurrence for the magneto pinion to
slacken off and disturb the ignition setting, and it is
not advisable to interfere with the setting unless it is
known to be at fault.
It is however advisable to check over the timing after
carrying out any adjustment to the magneto contact
points, as a slight variation of the points tends to
advance or retard the timing. (Opening the points
advances timing, closing them retards timing).
If the timing requires re-setting, first remove the
timing cover, and in so doing take care not to
damage the small nozzle in the timing cover which
feeds oil to the hollow crankshaft.
With the cover removed, take off the nut locking the
magneto pinion on its shaft, and with the aid of a
magneto pinion extractor (Fig. 10) release the pinion
on its taper. (Note that the pinion is held on its shaft
by a plain taper only, and can only be released with
safety by using the proper extractor.)
Fig. 9. Ignition timing,
Check that the fully open gap is correct to gauge (not
exceeding .012").
To re-set timing, turn engine forward until piston
reaches top dead centre on the compression stroke
(see Fig. 9). Now turn engine until piston has
".
descended 7/16
turn contact breaker in its direction of rotation until
the points are just about to open (not more than .002"
open). Lightly tighten the magneto pinion nut and
carefully check figures and positions. Then tighten
nut properly and re-check.
Fig. 10. Magneto pinion extractor.
9
With ignition control at full advance