Chicagoland MG Club: Tech Tips

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  Chicagoland MG Club:Tech Tips

Distributor Breaker Points

Function: The function of the points is to make and break the electrical circuit to the coil. Each time the points open, the circuit is broken, causing the magnetic field around the ignition coil to collapse. When this field collapses, a high voltage spark is created that fires the spark plug. The points must open sufficiently to break the circuit and minimize arcing. The points must remain closed long enough for the magnetic field to regenerate before the next spark plug is fired. The distance the points open is called "gap", and the amount of time they remain closed is called "dwell'. On a four-cylinder engine operating at 3,500 RPM, the points open and close 7,000 times per minute.

Problem Areas: Each time the points open, a very small amount of metal is transferred from one side of the points to the other. This transfer is uneven, and in effect closes the point gap. The second problem area is the fiber block that rides on the distributor cam and opens the points. This fiber block not only seats itself on newly installed points, but wears on points that have been in use for long periods of time. The combination of wear and metal transfer will eventually close the points completely, and the engine will no longer run.

Symptoms: As the gap begins to close beyond some rather broad limits, the engine will start to misfire under hard acceleration. As the gap closes even further, the engine will start to miss at normal road speeds. Further closing of the gap will result in an engine that is hard to start and impossible to make idle properly. These symptoms are very similar to those of fuel starvation caused by a faulty fuel pump, plugged fuel line or filter, or dirty carburetor.

Conclusion: Before taking the fuel pump apart or tearing into the carburetors - both messy jobs - check the point gap.

Additional Information: During the past summer, I assisted at least nine different owners that thought they had fuel starvation problems, when in reality they had points that had closed beyond their limits. It is a good idea to carry a spare set of points in the car, as a badly burned set of points are nearly impossible to set.

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