Arcing from coil HT post

[fig]

Hi all

I had to go and tow mrsfig home earlier when our 1971 single cab "Skedonkie" suddenly cut out a few km from home while carrying a load of manure.

I quickly isolated the problem to no spark and noticed the coil was arcing faintly across the bakelite top and it was getting very hot. So I replaced with a new one and the car started instantly. But now it was arcing strongly from the HT post and from the bakelite top to the fanhousing. Swapping out the HT lead to the distributor didn't help.

What would cause this? Is this yet another symptom of crappy condensors?

[retrovan]

We had the same problem with Johan Eagles Eagle on a trip to Outshoorn car show.

We then found the resistance in the HT leads where too high and it would rather jump to the nearest earth.

Changed to normal Wire HT cables and all was well.

Herman

[Dawie]

Seems that the coil is seeing an open circuit after the ht terminal. Normally the path to the plugs and plug gap prevent that voltage from getting too high. Even if plug gap gets too big with age the voltage rises with bigger chance of jumping elsewhere like plug wires or distributor cap.
Maybe the built in resistor in rotor went open. Or rotor not turning. Or cable between coil and distributor giving issues. Normally the end connectors have built in suppressors or aftermarket resistive wire.
Original Bosch coil have the external resistor built in, so it is supposed to run quite hot. It is oil filled and designed to take extreme heat indefinitely. Quality heat resistant materials like bakelite were selected.
Aftemarket plastic coils might be a different story.

[calooker]

I have had this happen as well, swoped out the dizzy that had a different cap and rotor, problem solved, but I cant tell you exacly the 1 item that was causing the issue.

[fig]

Thanks guys.

I think new HT leads are in order. And maybe rotor. Dizzy cap is new.

Adding to the above, the engine is newly rebuilt 1600 twinport original to the car. The only prior warning to cutting out was a for few days before the engine would run on 3 cylinders on cold start, but would smooth out once warm. Engine has so far done about 500km since rebuild with no issues except dirt in fuel lines in first few km.

[Terry Phillips]

Corrosion on all joints plug caps, dizzy leaves a coating that needs a good clean with sand paper. My 1/2 cents worth

[Dawie]

Also check that little carbon brush and spring inside centre of distributor cap

[fig]

I changed all the HT leads and Skedonkie is firing up first turn and running sweetly again.

When I removed the old ones I found that the insert that engages the spark plug on number 3 had come loose, so the spark was having to jump a huge gap to reach the plug. No wonder it was looking for easier routes to earth.