FORD CORTINA PITTING POINTS
Q
I have a 1973 Ford Cortina Mk3 on which I have recently replaced the original Autolite distributor with a Bosch unit. I now find that after around 50 miles the points are pitting up. I have replaced the points and condenser several times, but the problem comes back.
I have also now replaced the alternator, plus the coil ballast resistor wire, but this has made no difference. When the points begin to pit, I then suffer from poor running problems and so am keen to get this problem rectified. I have made various checks to confirm the distributor is correct, but I am at a loss as to why this problem has now arisen only after the distributor was changed.
AExcessive voltage can cause the premature pitting and although you have replaced the ballast wire, this only limits the voltage going to
the coil and does not control it. The voltage at the coil may still be too high, and this should be checked using a voltmeter with the engine running at about 2000rpm.
One of the main reasons for the higher voltage, providing the alternator output is correct, is that the earth return circuit back to the battery has a high resistance. One simple way to remove this from the equation would be to run a separate earth from the engine directly to the battery. If the problem still occurs, then other sources should be looked at.
As it is a new distributor which may have been coated at the factory with a fine film of oil to prevent it from corrosion, you should ensure that this is not the cause. A light film of oil on the points will cause the spark to arc across them, and this may well be the reason you are going through so many sets of points and why the problem was not apparent before the new distributor was fitted.