Ignition System Routine Maintenance

The workshop manual refers only to three regular ignition maintenance items, every 3,000 miles or 4,800km:
  • Lubrication of the advance mechanism (bob weights) with a few drops of light oil into the depression on the top of the central spindle and of the cam lobes with a bit of grease.
  • Check and adjust points gap
  • Clean and adjust spark plugs

Even the 12,000 mile service makes no mention of replacing the points although it does include replacing the plugs.

There is no mention of the need to check the timing as a regular routine, so this was regarded as only a side-effect of other work, such as new points or engine maintenance.

In practice, points will eventually become unserviceable because the contact surface is eroded by sparking. The decision to replace them can be based on visual inspection and anything other than a clean flat contact face is unacceptable. Check also for erosion of the cam rider. If the cam lobes have not been lubricated in the past, it is possible that some roughness may have been created on them and this roughness erodes the fibre or plastic cam rider on the points. The points progressively close and require frequent adjustment to maintain a strong spark.

After engine no. 12319, the upgraded DM2.P4 distributor was fitted. This accepted the later one-piece points sets that fitted with only one set screw. That set screw is loosened to adjust the gap and adjustment is achieved by inserting a screwdriver blade between two opposing V-slots. Rotating the blade opens or closes the gap.

Timing and point gap can be adjusted with the use of one of the multi-purpose meters available from accessory shops. The points gap is only the mechanical way of controlling dwell angle. That is to say the period (expressed as an angle or a percentage) during which the points remain closed during each ignition cycle. A meter that displays dwell angle shows whether the points gap needs to be narrower or wider, so that the specified 60 degrees of dwell is achieved. The meter will also substitute for the “bulb on a wire” traditionally used to identify when the points begin to open.

Misfiring problems can sometimes be caused by “tracking” in the distributor cover, which means that the high tension current goes to earth along the inner surface of the cap. Here again, visual inspection will reveal the problem because tracking leaves a black line and can also erode the cap itself. Dirt contamination and moisture will encourage tracking, so keep the distributor cap clean and dry.

If the rotor arm has been changed recently, it is also possible that the HT is shorting through it and onto the central spindle. This is a weakness of some batches of after-market parts manufactured in the far east. A later superior batch is now available and is coloured red for ease of identification.

For information on more complex distributor work, see the article "Getting the Best from your Distributor".

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