What causes a hot coil in Model A

3

31 Flyer

Junior Member
One of our club members has a very nice car and he takes extremely good care of it, but is experiencing a problem when he is touring. The car runs fine but will suddenly stop after running for some time on a tour. He has discovered that the coil is too hot to touch when this happens. If he waits for the coil to cool down the car starts and runs normally. The condensor has been moved to the firewall. The points are set perfectly and the hidden wire between the upper and lower plate is not causing a problem. He replaced the coil with a new repro unit but still has the same problem. The coils on other members cars are only warm on the same trip.
What might be causing this problem?
 
6V coil on a 12V system without a ballast?

compare amp draw of his coil with that of the cars without trouble....should be about the same
 
With the points closed and engine not running, the coil should draw about 4 amps.
I've seen some points where the copper strap rubs on the distributor cam, and this can cause the coil to be "ON" too much.

Make sure the cam is smooth and lubricated, or it will wear the rubbing block and cause the points to stay closed longer than they should be. This will increase the dwell time and overheat the coil.

A repro ignition switch can rub on the gas tank and cause the coil to be "ON" too much and overheat it. This usually results in a no start condition though.

Even though the engine will run with the condenser mounted at the coil, the condenser will function better when it's mounted by the points as intended. Also, when the condenser is mounted on the coil, it's on the wrong side of the switch, so if it was to short out it would kill the battery and also overheat the coil.
 
If the condenser should be on the firewall I would think that all the manufactures would have put it back there since it is cooler and out of the way. Every company got them as close to the points as possible.
 
Sunnybrook Farm said:
If the condenser should be on the firewall I would think that all the manufactures would have put it back there since it is cooler and out of the way. Every company got them as close to the points as possible.
Click to expand...


No that is not correct. The condenser is on the engine for important electrical reasons.

The extra length of wire can allow for burned points. The wire has inductance allowing for a voltage to be at the points that would not be there if the capacitor was physically close.
The condenser must be close to the points.
Think about it, if they could put it away from the heat back then they would have because heat is what really killed the early capacitors.

No matter which points you use (the 'modern' or original) I would recommend buying the burn out proof original style condenser. They are made with the modern quality more expensive (what like $.12 more?) capacitors. They just keep on working. My brother's is like 30+ years old now.
The V8 condensers are sourced from low bid contracts in china. The mustang guys have complained about them failing even new out of the box.
 
"The extra length of wire can allow for burned points. The wire has inductance allowing for a voltage to be at the points that would not be there if the capacitor was physically close. The condenser must be close to the points....., if they could put it away from the heat back then they would have because heat is what really killed the early capacitors. "
Yes I agree about the theoretics of it, but having driven many tens of thousands of miles on both my As with the condenser in the distributor, and equally many tens of thousands of miles with the condenser on the firewallall I doubt if in practise it has any significance in the world of low revving understressed engines like the stock A?
( I totaly agree about some lousy condensers on the market at present )
 
How much voltage is the generator putting out, if at full rpm's he's putting out 8V give or take, on a long run he could just be simply throwing to much juice at the coil causing it to over heat and give the symptom you are referring to. Just another avenue to check.


Saving iron from the scrap pile one piece at a time
 
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