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[tippi]

Hi there,
Today my engine suddenly stopped working without any pre-warnings; first feeling on the bike was like no fuel or ignition switched off (really nice in peak traffic). Back home by means of a trailer it turned out that the moving point moved as it should, and the points gap was ok as well. But when I got the points in closed position (decompress and kick), I had no amp meter reading and a test lamp also showed that there was no current through the closed points. After cleaning the points, everything seems to be ok right now (engine runs). But I am little afraid regarding my next ride. Can corrosion on the points happen this suddenly? I would have expected pre-warnings, such as poor engine power, misfiring etc. Points operation is about 1500 miles ... Thank you very much, regards Peter.

[Dennis C]

Yes it can happen that quickly. It would be a good idea to check/replace the condenser if the points looked burnt.

[jefrs]

This article shows and explains the points and condenser pretty well even though it's for an Austin 7 http://www.da7c.co.uk/technical_torque_ ... citors.htm



Wear on the heel of the points (see pic in link) against the cam will close the points gap. It is the opening of the points that creates the spark. The fully open gap is usually about 16 thou. When the heel wears the gap gets smaller and smaller and thus starts arcing which apart from causing weak and false sparks at the plug will create pitting of the contacts. The contacts can be filed flat again to some extent but soon need replacement. The condenser is there to quench the contacts arcing so we get a full spark from the coil only when we want it. The heel is usually Tufnol, a phenolic resin-fabric material with good wear and insulation properties, there should be a drop of lube on the cam.



Should the points not be closing indicates the points have slipped on the screws somehow so the heel is held too tightly against the cam. Usually if the screws loosen the points' spring will hold the contacts in the closed position, it is not normal for points to tighten themselves against the cam.

[jefrs]

If one of the contact pads has flown off you will get open points. You should have two phos-bronze contact pads on the points.

[Dennis C]

Phos-bronze?. I think you will find tungsten is the preferred material for the contact disc.🤓🤓

[ric]

A points failure that wasn't fixed at the side of the road?

There will be several electronic ignition naysayers reaching for their voodoo dolls before this day is over.

[PeteF]

I don't think phosphor bronze contacts would last long.

[papasmurf]

I thought contacts are an alloy of 80% platinum/20% iridium.

[jefrs]

Well I can't ask my old dad what he made them from as he's passed away. Phos-bronze was used, and silver-copper and silver-cadmiun-copper are used for switch contacts. Tungsten is used but not only hard but difficult to machine, which puts the price up. Platinum/iridium likewise expensive. Switch contacts are usually formed by die-punch in a big press. There's not much physical wear on the contacts but they need to be hard to resist the rapid repetition and must conduct electricity well and resist arcing. They have to resist electrical eroding. Phos-bronze (of which several alloys) is hard and has a high copper content, the silver-copper alloys tend to be softer. One of the ways of machining hard tungsten (and titanium) is spark erosion.

[PeteF]

Yes but spark erosion is used for accuracy, not because the material is difficult to machine. Spark erosion removed microns at a time.
I find the electrical conductivity of phos-bronze is only described as "fair" an all the tables I can find.
I can not find any reference to it being used for breaker points (though it is used for switch contacts)