Any variation in timing can be obtained only by moving the contact breaker plate
“8” Fig. 2, which can be rotated through a very small angle after releasing the screws
“D”. Do not forget to re-tighten them securely after the adjustment has been made.
It is emphasised that this is a “works” adjustment rather than one which the private
owner is ever likely to carry out. To check the actual timing ignition, it will first be
necessary to remove the primary chain cover and then adapt a degree plate to the
engine main shaft, accompanied by a suitable pointer connected to a convenient stud,
as illustrated in Fig. 3. Next, determine the top dead centre position of the piston.
Rotation of the engine through several degrees near this position produces a very
small movement of the piston which is difficult to detect. If the cylinder head is
removed a straight-edge can be laid across the top of the barrel to act as a stop for the
piston.
Bring the piston gently up to the straight edge by rotating the engine as far as it
will so, first in one direction and then in the opposite direction. If degree plate
readings are taken in each position, the point mid-way between them is easy to
calculate and this will be an accurate top dead centre. Adjust the timing disc until the
zero mark corresponds with the pointer.
From this position rotate the engine BACKWARDS by 18-degrees and check that
with the piston in its new position, the contact breaker points are just separating (not
more than ·002 in. open). If they are open by more than this amount the timing is
advanced excessively and vice versa.
It is essential to ensure a correct contact points gap before setting the ignition
timing.
