Technical burnt points

I have a strange problem, points in sbc burning very quickly. 10-15 minutes run time. I have checked the wiring, I have 13 volts on ing. side of resistor and 7 on distributor side. Car runs good for 4-6 minutes and then goes to missing and dies in 10-12 minutes, points burnt blue.

 

what coil?

have you replaced the condenser?

is this a new problem on a car that ran fine before, or is it a fresh build?

 

Over charging???

 

Just some things that can be prob;;;
Bad or wrong condenser,can burn them fast.
There are still coils around that are 6volt/that must have a 50watt resistor to use with 12volts. The wiring for same comes through the starter selinod an can be hooked up wrong.= running 12v to 6volt coil=coil gets really hot an fails but also kills points.
Old points that have been filed,burn faster then new. Leveing ign. on if points are closed at the time can burn them,etc.

 

7 volts to the points is too much.

 

Your house is filled with points (light switches) with 117v on them. Which is to say high voltage isn't the issue.

The ignition coil is a huge inductor which is switched on/off and can causing very large spikes at the contacts of the switch. In a perfect world the voltage spikes are quelled/reduced/subdued by adding a condenser at the points which is carefully matched to the equal the coil's impedance but have characteristics just the opposite. These voltage spikes, if allowed, cause metal to migrate from one contact to the other, sort of a plating action. Hence they cannot be allowed to occur because those peaks soon short the circuit as the points no longer open.

The voltage across the points should be close to pure DC so the points last a great long time. In the laboratory, they carefully match condenser to a given coil for you, thus preventing pitting and publish the size of condenser matched to a specific coil. Given adequate time you could duplicate the lab technique yourself (but not on an engine) by noting the mountain of metal which building into a peak on one side of the points. Too large a condenser will cause the metal migration to move from bottom to top while too small a condenser will cause the metal to migrate from top to bottom.

I realize inductance and reactance aren't part of the electrical world outside of electronics, so I hope this provides a basic understanding of the circuit. It should be noted that modern cars will in addition, have a condenser on the battery side of the coil to quell noise which interferes with the radio as the wiring from battery to coil is also inductive and that condenser neutralizes voltage at the coil to again convert it to pure dc.

Bottom line - Bob's problem is improper condenser. My vote is with Dana, coil/condenser must be matched.

 

I had a 70's Ford in the early 80's that started burning points after a tune up. Not as fast as you are though. Finally determined that the condensers from the parts store were the cause. Got the correct one after about 3 sets of points and condensers and things went back to a normal life expectancy. Good luck with it.
-Dave