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checking distributor caps and rotors

S

susandiane

Member
In days of happy memory we checked caps and rotors with the output side of a model T coil to be sure the continuous spark from the buzzer coil didn't go places it shouldn't. Many times it would arc to an
invisible crack or a chip near a terminal. Is there anything like that sort of tester today that a person can afford for routine tests?
 
I have never heard of that test before. Sounds interesting. Should still be able to get your hands on a model T coil pretty easy.
 
Run the machine in the dark and look for sparks around the high-tension parts.

ZAPPING what may be a good cap with high voltage with no place to go may start a "carbon track", leaving a permanent place for spark to jump where it shouldn't.
 
Which I suppose is why when cranking a spark ignition engine with the plug wires unhooked, they want you to ground them.

But then having a plug wire jump a spark just outside a spark plug hole, as you crank an engine which is delivering fuel, is an interesting experience!
 
While it is not a fun way but it a super cheap way to test a cap is fire it up if it will run and hold the cap. If the cap is bad you will find out before you get a good hold on the cap. I learned that back when I lived in Mississippi and my dads GMC pickup truck would not run right if we had a rainy day. He took it to a shop and they could not figure it out but I did because I reached in and tried to garb the distributor cap and I sure as heck let go fast We found for some reason it liked to kill distributor caps for some reason so we kept a new cap in the glove compartment for time when it would go bad
 
Some OOOLLLDDD magnetos had "safety spark gaps" built into the phenolic "cap", that were spaced wider than sparkplug gap, giving spark a place to go to ground if a wire fell of (or some such event), rather than "carbon tracking"/destroying the "distributor cap" and ruining it.
 
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