Top of coil coming out of the can

[Sledge303]

This past week I had an ignition failure, where the engine sputtered a bit and quit.
Set in a parking lot for a short time and it started back up, ran another few minutes, sputtered and quit in the parking lot at work.
I had an aftermarket ignition module installed and so swapped it out for a used USGI unit.
After the swap M151A2 ran for over 40 minutes at idle, fast idle (using throttle) and drove around a bit.
Next day I drove it home (about a 20-25 minute run with a few hills).
During the swap out work I noted it was hard to get the black wire over the post on the coil.
Seemed odd as I don't remember having any undue effort to get in on when the coil went in last time.
So I had a look at the (USGI) coil out of the distributor while everything is disconnected and I swear that the black top (which has the connections) has moved up out of the metal "can" that the coil sets in.
I am thinking it has moved at least an eighth of an inch, comparing the lip on that black top with the top edge of the "can".
Compared to another older USGI coil I have it looks a bit taller, which would have made the wire tight to remove.
I tried applying pressure (carefully) in a vice to see if the top would move down, but it feels quite solid.
Has anyone else ever experienced this?
I am wondering the cause, what could swell in a coil housing?

Richard

[rickf]

The symptoms of the shutting down and cooling off to restart are classic coil failure. It is possible that the module was failing but it is also possible that the coil failing is taking out the module. If the coil is swelling up it is definitely failing. As far as what could swell, it is mainly the insulation on the wires but it could also be the cooling oil expanding. It seems that some are oil filled and some are not from what we have seen but if you take the coil out and the housing is full of nasty oil do NOT get it on you because there is a good chance it is a Dioxin oil which is very toxic.

[Walter]

Good Afternoon Rick & Company:

At an MV show last year I came across a fellow who was selling both NOS and used T/O, M-Series coils he offered the following tests to verify whether the coil was any good or not. He demonstrated it on several to make his point. I certainly agree with Rick that is it is swelling and leaking it is junk. But what if it is not? Has anyone seen or heard of this method in checking coils --

Here are the instructions for checking out the 24 volt coils. On your multi meter set it for Ohms. Set it for the 10-20 ohm scale. Zero "0" the ohm meter so that when touching the two leads it reads"0". Now measure the resistance between the two low voltage side terminals. It should read between 5-6 ohms.

Now reset the scale to 50,000 to 100,000 ohms. Re-zero the meter. Touch one lead to one of the low voltage terminals and the other lead to the center post or the high voltage side of the coil. Either terminal will work. Your ohms reading should be between 14,000 and 21,000 ohms.

Anything less than those readings and the coil is probably shot.

Thoughts?

Regards,

Walter

[rickf]

Those are the standard readings for the American coils on the primary side but the secondary should be in the 11,000 to 14,000 range. What you were given was the range for the Chinese coils on the secondary. The Chinese coils would read ~11 ohms on the primary and 15,000 to 20,000 plus on the secondary. With all of that said it is still possible for a coil to fail and read good, at least in the beginning stages of failure because what is happening is one of the wires, usually a primary wire, has broken and as it heats up it pulls apart which opens the circuit and the vehicle dies. Once it cools down the wires come back together and it will run. It will also show a good reading until the broken ends start to build up carbon from arcing.

[Walter]

Good Morning Rick:

Many thanks for the clarification. As I may not have mentioned in my last post this was my first exposure as to how to actually check the coil. I have shared it with a number of other good mechanics and most of them had not heard of it before. Yes, I uinderstand that a coil could possible check out within tolerances even if it is i the early stages of failure, Before I had this QC information I had a similar situation occur on my M-38. When it was cold it would start and run fine, but after a while it would run erratic and then die completely. The next day it would again run fine in the morning. In essence as it heats uo, the break expands and looses continuity.

Thanks again for explaining the differences between the American coils and the china coils.

Regards,

Walter

[rickf]

Another of the symptoms is backfiring out the exhaust as it is dying. This is caused by the disconnect/reconnect or the coil as it is on its way to total disconnect. Remember as a kid how we turned the key off running down the road and then back on to produce a loud backfire. ( and occasionally blow dads muffler apart!)

[m3a1]

Examine your Ignition module closely, as well. If there was enough energy there to pop the cork on that coil, I would bet there have been some serious side effects to your IM.

Check the bottom of the well where the coil resides, as well as below the IM. Coils poop out oil when they superheat, IMs poop out their potting material when they superheat. All of this poop goes right on your spark advance mechanism...which then won't work worth a darn because it'll be all gummed up.

Universal personal protective precautions for cleaning up the mess. You don't have to wear an encapsulative suit but do use good quality gloves and eye pro and throw-away rags. Don't get it in your or on you. It's certainly not a death sentence if you do get a bit on you but clean it off ASAP. Dispose of your cleaning rags (don't put them in Momma's washer).

Cheers,
TJ

[Sledge303]

I thought it may be useful to add a picture of the coil with the top coming out next to a "normal" 24VDC MUTT coil.
the o0ne I just removed is on the right.

Richard

IMG_20220227_1359572.jpg

[Mark]

Those are the kind I have on my jeeps

[Sledge303]

I have been thinking about it, I suppose there is nothing that can be safely done with that coil that seems to be forcing up its top.
I have driven with it installed, and had thought of keeping it as an "emergency spare".
What I keep coming back to is the possibility of the top coming out of the can, and then leakage.
Disposal seems to be the only option.

[rickf]

If the coil is swelling then it is failing. You could keep it as a spare but would you trust it? I wouldn't. It is entirely possible that the ignition was left on and the coil overheated and that was what caused it to swell up. You said you had to replace a burnt module. That was probably the result of the same thing. But the matter remains that the swelling is caused by the insulation cooking on the wiring so it is just a matter of time before it shorts out and you are dead on the road.

[Lou]

I agree with Rick on this one. The coil could short out in this condition and burn out another ignition module. Also, with the coil top high like that it is putting additional force on the spring and distributor cap and can crack it and cause it to fail. Sorry, but that coil is junk now.

What kind of ignition module were you using? It is possible it caused the coil to overheat and caused the failure. Many do not know that the ignition system is a “tuned system”. Meaning that the inductance (AC resistance) of the coil and the components within the ignition module have to be matched. If anyone here is familiar with radio terms, it would be like having a 1:1 SWR on a radio transmitter. Any deviation here will cause either the coil or ignition module to overheat and fail. This is why the china coils cause issues, they are not the proper Inductance or measurable DC resistance.

One thing you can do to help us is actually measure the primary and secondary resistance of the bad coil and compare it to the readings of the new coil.

[m3a1]

It's time to give that coil a decent burial.

[Sledge303]

I agree with Rick on this one. The coil could short out in this condition and burn out another ignition module. Also, with the coil top high like that it is putting additional force on the spring and distributor cap and can crack it and cause it to fail. Sorry, but that coil is junk now.

What kind of ignition module were you using? It is possible it caused the coil to overheat and caused the failure. Many do not know that the ignition system is a “tuned system”. Meaning that the inductance (AC resistance) of the coil and the components within the ignition module have to be matched. If anyone here is familiar with radio terms, it would be like having a 1:1 SWR on a radio transmitter. Any deviation here will cause either the coil or ignition module to overheat and fail. This is why the china coils cause issues, they are not the proper Inductance or measurable DC resistance.

One thing you can do to help us is actually measure the primary and secondary resistance of the bad coil and compare it to the readings of the new coil.

The ignition module that was in operation with this used USGI coil was one of the new manufacture ones that comes in a white box.
It was installed by the previous owner.
I had some ignition trouble last summer that I attributed to the coil, now I see it was the module and the other coil is back in service.
So, today I am running a used USGI coil and used Swiss controls module.
I think the rotor is USGI too.
I have ohmed out all 3 of my coils, the readings are in line with the values published in several places on this forum, this included the coil I pitched today.
So I have a operating ignition, and a spare used USGI coil and ignition module.
Now I just need to dial in the timing for a MUTT that lives at 6K feet of altitude.
It doesn't like the hills around town too much!
My carb is a Billy Brooks rebuilt ZENITH 13660, Ordnance number 11681709, done when this MUTT was in (low altitude) California and driven by its last owner.

[rickf]

Timing should be set right on the line, altitude has nothing to do with timing and changing timing does nothing for performance, at least not at the cost of drivability. 6,000 ft altitude should not affect the drivability at all but if you feel it is sluggish then back out the idle mixture screw about a half turn. You do not want it missing at idle but a hair rich at idle will eliminate any flat spots at cruise. These engines need to have all of the parameters set correctly to run right so the valves need to be set on the money also.