BSA D14/4 BANTAM SUPREME D14/4 BANTAM SPORTS, Руководство по ремонту

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D14/4 ENGINE B18
Piston Position
Before checking the ignition timing, the piston must
first be set at the recommended position before top
dead centre on its compression stroke. This position
can be accurately set with the aid of a degree plate.
The outer timing cover should first be removed and
the degree plate mounted centrally on the engine shaft,
against the rotor. A suitable pointer should then be
attached to some convenient part of the engine with
the point adjacent to the plate (see Fig. B22). Rotation
of the engine through several degrees near the top
dead centre position produces very little piston
movement, making the actual top dead centre very
difficult to find. It is a good point therefore to use a
suitable stop (such as a dummy plug with a projection
into the cylinder head) so that the piston can be
brought gently against it.
Bring the piston slowly up to the stop by rotating the
engine as far as it will go, first in a clockwise
direction, then in an anti-clockwise direction. Take
degree plate readings at each position and calculate the
point midway between them. The result will give you
an accurate top dead centre of the piston. Loosen the
timing disc retaining nut and turn the disk until the
zero mark corresponds with the pointer.
From this position, rotate the engine backwards to
obtain the desired reading of 16½° on the plate.
Setting the Ignition Timing
With the piston at 16½° before top dead centre, the
contact points should just be separating.
FIG. B23. Setting the ignition timing.