Ignition timing and contact breaker gap (dwell angle) check - OHV engines (6000 Mile (10 000 Km) / 6 Month Service)
Contact breaker gap (dwell angle)
1 Access to the distributor is improved by removing the air cleaner unit.
2 Prise down the distributor cap retaining clips or remove the securing screws, as appropriate. Remove the distributor cap and rotor.
3 Apply a spanner to the crankshaft pulley bolt and turn the crankshaft until the distributor points are fully open, with the heel of the cam follower on the highest point of one of the lobes of the cam.
4 Using feeler blades, check the points gap.
Checking the contact breaker points gap using a feeler blade
If the blade is not a sliding fit, release the screw at the fixed contact so that the contact will move and adjust the gap to that specified. Retighten the screw, refit the rotor and cap. Take care not to contaminate the points with oil from the feeler blades.
5 This method of adjustment should be regarded as second best as on modern engines, setting the points gap is usually carried out by measuring the dwell angle.
6 The dwell angle is the number of degrees through which the distributor cam turns during the period between the instants of closure and opening of the contact breaker points. Checking the dwell angle not only gives a more accurate setting of the contact breaker gap, but this method also evens out any variations in the gap which could be caused by pitting of the points, wear in the distributor shaft or its bushes, or difference in height of any of the cam peaks.
7 The dwell angle should be checked with a dwell meter connected in accordance with the maker’s instructions. Refer to the Specifications for the correct dwell angle. If the dwell angle is too large, increase the points gap. If it is too small, reduce the gap.
8 The dwell angle should always be adjusted before checking and adjusting the ignition timing, as follows:
Ignition timing
9 Before checking the timing, check and adjust the dwell angle with the engine at normal operating temperature.
10 Increase the contrast of the notch in the crankshaft pulley and the appropriate mark on the timing index (refer to Specifications) by applying quick-drying white paint.
Ignition timing marks - mechanical ignition system
11 Connect a timing light (stroboscope) in accordance with the manufacturer’s instructions.
12 Start the engine and allow it to idle.
13 Disconnect the vacuum pipe from the distributor and plug the pipe with a piece of rod.
14 If the timing light is now directed at the engine timing marks, the pulley notch will appear to be stationary and opposite the specified mark on the scale. If the marks are not in alignment, release the distributor clamp pinch-bolt
Distributor clamp plate pinch-bolt (arrowed)
and turn the distributor in whichever direction is necessary to align the marks.
15 Retighten the pinch-bolt, switch off the engine, remove the timing light and reconnect the vacuum pipe.
16 It may now be necessary to check and adjust the engine idle speed if the distributor setting has to be varied to any extent.