4. Set the engine idling speed to 500 r.p.m. when the -~ engine is properly warmed up.
5. With the engine running at 500 r.p.m. observe the fixed T.D.C. pointer with the stroboscopic timing light. If the ignition timing is correct the white line on the crankshaft damper will appear opposite the white line on the fixed pointer.
6. If the Ignition timing is not correct loosen the distributor holding down bolt and rotate the distributor, so that the correct timing is obtained while the engine is running at 500 r.p.m. Clock-wise rotation of the distributor advances the ignition and anti-clockwise rotation retards it.
7. Tighten the distributor holding down bolt and re-check the timing.
8. If no further tests are to be made reconnect the vacuum feed pipe and remove the test equipment.
Checking centrifugal advance action
Without removing distributor
The distributor centrifugal advance action can be checked without removing the distributor from the engine, by connecting a stroboscopic timing light to No. I cylinder sparking plug, and a tachometer to read crankshaft r.p.m. The ignition advance angle in crankshaft degrees for a given engine crankshaft speed, with the distributor in position on the engine, is always the static ignition advance setting plus the distributor advance angle for that speed multiplied by two.
When checking centrifugal advance only the vacuum advance pipe must be disconnected from its most con-venient attachment point.
Example
These figures are taken from the Data Section and are —~ those used for this check.
Static ignition setting ... ... 60 B.T.D.C. Engine
R.P.M. ... ... ... ... 3200
Distributor R.P~M. (3200+2) ... ... ... 1600 Distributor centrifugal advance for
1600 R.P.M 5 1/4 deg.-7
(average 6 deg.)...... ... ... ... ... ... ... 6 deg
Ignition advance for 3200 r.p.m. is therefore 6 deg. B.T.D.C. ± (6deg. x 2) =180 B.T.D.C.
It should be noted that the distributor r.p.m. and advance angle must be multiplied by two to obtain the equivalent crankshaft r.p.m. and crankshaft advance angle, because the distributor runs at half the engine speed.
To make this check: —
- If not already done clean and paint the fixed T.D.C. pointers, and the static ignition setting before T.D.C. on the crankshaft damper rim, with quick drying 7-paInt.
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2. Paint another line 180 B.T.D.C. This second line will be easier to recognise if it is painted with yellow paint. l8 deg. B.T.D.C. Is obtained by marking off 6 deg. (two 3 deg. spacings) before the 120 B.T.D.C. position, with a pair of dividers.
3. Using the stroboscopic timing light check that the static ignition setting has been correctly set as previously described.
4. If not already done disconnect the vacuum feed pipe to the distributor at its most convenient end.
5. Connect a tachometer to the engine and run it at
3200 r.p.m. while observing the fixed T.D.C. pointer with the stroboscopic timing light. If the centrifugal advance is operating correctly the yellow line (180 B.T.D.C.) should appear opposite to the white line on the fixed pointer to within 2 degrees.
6. With the engine Idling and still observing the white line, gradually increase the engine speed. The distance between the white line on the damper rim and white line on the fixed pointer should increase with rising engine speed. This Indicates that the centri-fugal advance is operating. Decreasing the speed should give the opposite effect. Jerky movement of the mark on the damper rim while accelerating or decelerating indicates sticky centrifugal advance mechanism.
Note—The foregoing is a very useful check but as it is only made on one cylinder no indication is given of the condition of cylinder phasing timing. At high mileages this can be affected adversely by cam lobe and distributor shaft bearing wear or excessive wear in the distributor drive train. These faults can only be detected; with the distributor on the engine, by the oscilloscope (scope) type of test equipment.
Checking vacuum advance action
Without removing distributor
The throttle should be opened to give an engine speed of 1200 to 1500 r.p.m. and the vacuum pipe to the distributor connected and reconnected while observing the line on the crankshaft damper rim. This should retard and advance as the pipe is removed and refitted. Blockage of the vacuum feed pipe, vacuum feed hole, or jamming of the contact breaker plate will prevent correct vacuum advance action.
This check gives an Indication that the vacuum advance is working. For a more accurate check it is necessary to remove the distributor and test it on a distributor tester and also to check the vacuum at the carburettor con-nection. This should be approximately 2 in. Hg. at 1,000 r.p.m. and 22 In. Hg. at 1,800 r.p.m.
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