Hot coil

J

JOHN-WA.

Junior Member
Went to lunch with a friend yesterday on the way back his car started missing, backfiring and died about four times he was able to restart and get it home, checking things out he found that the coil was so hot he could touch it for only a few seconds (in the past two years he has had four coils that failed) where should we start looking ??
 
I wonder if he has a wire or ignition switch shorting to ground between the coil and points? That could burn out the coil.
 
If an oil filled coil is used it must be mounted with the tower and wire connections pointing up. The oil cools the windings. Model A coils were tar filled. If the coil is oil filled, it has been pointed out that you can shake the coil and hear the oil sloshing inside, if it is an oil filled coil. Two other causes of early coil failure are too much air gap at the rotor tip or too much spark plug gap. I don't go over .035 on either with points ignition.
 
I find that whenever something goes out that many times, it is the symptom and not the problem. I would do a good electrical system test. There was a nice write up in the Restorer around 2000. I will look it up tomorrow.
 
JOHN-WA. said:
A-12000
Click to expand...

Just wanted to be sure of the correct coil. Now that you have confirmed he is buying a coil from the vendors that are used with Model A's with no problems.

If the wiring were shorted to ground all the time I would think the circuit would never open and the high voltage would not collapse and go out to the plugs

I'm thinking; points, specifically gap, or a bad cap.

A small gap would allow the engine to run (poorly i would think at higher speeds) and a bad cap could be causing a path to ground but not a dead short causing a drain all the time.
 
Hot coil Update

He said he was check things today and his fuse holder was hot but the fuse was OK. I think he needs a witch doctor
 
I would install an electronic voltage regulator in the generator. The fuse holder being hot could mean a poor connection, and that can lead to high generator voltage output, unless he has an EVR.
 
Condenser could be the culprit, worth while changing it and make sure everything including condenser is earthing properly.
 
Like Tom mentioned, it could be a short somewhere.

I had a problem like this where the coil felt hot. Before I noticed the coil being hot, driving it home from a car show, the car acted similar to what you described. It would run OK for awhile then cut out and start going again. It finally died and I had to pull it home.

What I found was the key switch, which was after market, had shorted against the gas tank. I had one of the wires that was attached to the switch, stick out so that it touched the gas tank. The rig had run this way for over a year but the paint finally scratched off the gas tank and it shorted.
 
Make sure the black wire is on the - side of the coil and the key wire is on the + side of the coil. the coil will work the other way but the coil will heat up. also make sure all connections are clean and tight .
 
I had a similar problem this year with a Farmall Cub tractor I have-all the same symptoms. It turned out to be a poor connection to the voltage regulator-I only found it by using a continuity checker.
 
One person suggested that the points gap could be too large, and another suggested that it could be too small!

I vote for the gap being too small: this would result in a larger dwell angle, which means that current is flowing through the coil too much of the time. Or maybe the cam profile could be all messed up. A dwell measurement would be very helpful for diagnosing the problem.

Doug
 
You must log in or register to reply here.
Back
Top