MG MGA Twin Cam Workshop Manual page 72

To set the distributor proceed as follows:
1. Turn the crankshaft in the direction of rotation until No. 4 piston is at T.D.C. on its
compression stroke. This can best be effected by turning the engine and observing the
valves. When the valves are 'rocking' (i.e. exhaust just closing and inlet just opening) on No. 1
cylinder No. 4 piston is approximately at T.D.C. on its compression stroke. If the engine is
now rotated until the notch in the rear flange of the crankshaft pulley is in line with the small
projection on the timing chain case the piston is exactly at T.D.C. (see Fig. B.3).
2. Set the contact breaker points to .014 to .016 in. (.35 to .40 mm.) when in their position of
maximum opening.
3. Insert the distributor into its housing, and engage the drive dog lugs with the drive shaft slots
(both of which are offset) by slowly rotating the rotor arm.
4. Screw in the two bolts securing the distributor clamp plate to the distributor housing but do not
tighten them. Failure to leave these bolts slack will cause misalignment of the distributor
resulting in excessive wear of the drive gears.
5. Position the distributor so that the vacuum control unit side of the body is uppermost with the
unit diaphragm to the rear.
6. Rotate the distributor body anti-clockwise until the points are fully closed. Then slowly rotate it
in a clockwise direction until the points just commence to open. Secure the distributor body in
this position by tightening up the clamp plate pinch-bolt and nut, give the engine a few turns to
allow alignment of the gears to take place, and then fully tighten the two clamp plate bolts.
Check that the rotor arm is opposite the correct segment for the cylinder which is at the top of
its compression stroke.
IMPORTANT.—To obtain an accurate setting an electrical method should be used to
determine the actual position at which the points break, and the following method can
be used:
With the low-tension lead connected to the distributor, turn on the ignition switch and
connect a 12-volt lamp in parallel with the contact breaker points (i.e. one lead from the
distributor low-tension terminal and the other to earth) and turn the distributor as
detailed in paragraph 6 until the lamp lights, which indicates that the points have just
opened.
7. After locking the distributor, re-check the timing.
Fig. B.3 When the groove in the crankshaft pulley coincides with the small projection on the riming
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