To reset ignition timing. As the ignition advance is limited to ¼"
B.T.D.C, this setting is critical and must be carefully carried out. The
automatic ignition control unit is a taper fit on the camshaft, retained by
a central bolt. To remove this unit take out the retaining bolt, use in its
place a withdrawal bolt, Part No. 042247. Screw home this bolt—do not
use undue force—then tap the head of the bolt lightly which will separate
the unit from the shaft.
NOTE—The contact breaker cam is detachable and if it is inadvertently
removed, the timing should be rechecked after refitting the cam, before
attempting to start the engine.
VALVE TIMING
Lightweight, Including Scrambler Models
The cam wheel, also the small timing pinion which drives it, are both
marked to facilitate assembly.
If for any reason, the cam wheel is removed, to re-assemble rotate the
engine until the piston is on T.D.C. of the stroke, the mark on the small
timing pinion tooth will then be at 11 o'clock. Take up the cam wheel,
raise both cam followers, then introduce the cam into the crankcase
with the mark on the tooth gap to register with the mark on the small
pinion.
These markings have been selected to give the most effective valve
timing and best engine performance,
To check the valve timing, as a single piece camshaft is used, it is only
necessary to record the inlet valve opening also the exhaust valve closing
positions to verify that the valve timing is correct.
The average valve timing, taken with .010" rocker clearance is:—
Inlet valve opens 40° B.T.D.C.
Exhaust valve closes 40° A.T.D.C.
See TAPPET ADJUSTMENT for running pushrod clearance.
IGNITION TIMING—COIL IGNITION
Heavyweight Models
To understand the principle, a study of illustrations should be made.
The automatic timing control is a taper fit on the shaft for the inlet cam,
retained by a central bolt. The cam separating the' contact breaker points
is rotated by two pegs engaged in the plates for the unit springs. As the
cam is detachable, the position of the cam should be noted, before it is
removed. Before setting the ignition timing it is essential to check the
contact breaker gap.
Checking contact breaker gap. Remove two screws securing the cover
mounted on the timing case, also the cover. Rotate engine to fully
separate contact points.
Check gap which should be .014—.016".
To adjust the gap release slightly the two inner screws securing the
fixed contact plate and adjust the gap as required by moving the pivot
plate in the required direction.
Removing the automatic timing control. After taking off the cover:
Remove the two screws passing through the slotted holes in the fixed
contact breaker plate and remove the plate.
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