New guy, basic question.
Can model T ignition coils be repotted with something other than the tar that is in the coil boxes after wiring in replacement capacitors? Would silicone sealant work?
Yes, you could use something other then tar but probably not silicone. Silicone is corrosive. And of course someone in the future will wonder quite loudly why you did not use tar when he tries to get in and repair it again.
Tar has worked well for over 100 years and is easy to work with. Many would recommend that you don't change something that works well.
No to silicone! Gurr! I have one that I need to redo that someone put silicone in, what a mess to clean out. Use tar.
There's nothing wrong with your question Andy. Welcome to the forum as well. Ron Patterson and other have posted many photos over the years of various things found inside coils. None of them will stand up to another 100 years of heat and cold cycles as well as tar does. It provides both mechanical stability and seals against humidity. It really is the best way. Things like silicone or RTV or expanding foam will cause problems in the long run. After all of the work required to CORRECTLY rebuild a coil, taking a shortcut in sealing it really makes no sense.
Again, welcome to the forum Andy.
The recommended tar is Type III Steep Roofing Tar. Most roofing companies probably have scraps lying around they would probably give you.
Our phone company used silicone on the under ground pit joints, now starting to give trouble after 25 years! I don't think I'll live long enough to see it give me any grief in a coil box!!
I don't think all silicone sealants have the same properties. Some are better than others when it comes to electrical degradation. What to look for I wish I knew. Tar may be the best long term if you can't find the silicone with non-corrosive qualities, if one exists. Squirting some goo in would sure be simpler. Several folks have shared before that such a substance is made. May not be readily available outside industry circles?
The best product to use is steep grade roofing asphalt type III.
That's what I use in my rebuilds. You may be able to get a small piece from a roofing distributor. I like tar since it insulates and stops interior parts from rattling around.
I hope this helps,
Just wonderin' - in a pinch would candle wax work?
Candle wax has too low a melting point and will not work.
You know it isn't strictly necessary to totally replace the space with tar. Wood blocks or spacers can be cut to take up a lot of the open area left by replacing the large orig. capacitor with a newer/smaller modern cap. The remaining space can be filled with the tar you've salvaged from removing the old cap. From the first cap. replacement I did to the present, about 20 total, I've always successfully pried off the wood side of the case that the cap is on. It makes replacement insanely easy and salvaging the tar you pull out onto an open newspaper is no problem. I dump it into a small metal can with a vice grip on it and a lip bent into the top and soften it with a propane torch. I've never needed to buy any extra tar. In fact I have a small stash left over from all the coils I've done.
By the way: there's no way in hell I'd re-fill that space with silicone.
I agree with Charlie B. Dang, that rhymes. Some wood blocks will take up the extra space. Just re-melt the tar you dig out. When I first started building coils, I used tar out of coils that had bad secondaries. I finally got a 'drum' of proper roof tar from a roof contractor. It was a damaged and they didn't even charge me for it.
is it possible to melt out the tar with a heat gun? Not a hair dryer, a heat gun.
Any hints on this messy project??
(One reason I like buying rebuilts from Ron--he deals with the mess!)
Dig the tar out with a small tipped screw driver. Just be careful to stay away from the coil windings as one slip will ruin a coil.
I've never tried to melt it out. My guess is that it would be a mess. Molten tar would run into the narrow grooves where the 'door' slides in.
Guys, it is really no big deal. Just dig it out. It's not particularly 'gooey'. It usually comes out in chunks. The biggest mess is the tiny little bits that break off. Just do it over some newspaper, then use the newspaper as a funnel to pour the little stuff into whatever you are melting it in. A little mineral spirits on a rag will clean it off of your tools and your skin or most any hard surface. It really is no big deal!
Someone on this forum sent me a shoe box full of tar for the price of shipping.
I keep an old pot and a hotplate just for the purpose of re-potting.
(A word to the wise)
Let the re-potted coils cool for several hours before handling.
Someone else gave me that same advice but I knew better???
I got a nasty burn when after a few minutes, I decided to move the coils.
No matter how hard or fast you sling your hand back and forth,
you will not be able to generate the centrifugal force necessary to
dislodge semi-molten tar from your hand.
(I speak from experience)
I have melted the tar out in the oven on low temp. One thing I did do was put tape over the groove to keep the tar out of it. That worked. I did them standing up on a sheet pan with a piece of wood under them to raise them up off the pan. Oh I have a gas oven done it twice, haven't blown the door off yet! Some smell, not bad.
This is what I will be using for coil repotting. I bought the 50 lb bag locally.
My '23 TT coils had newspaper stuff around the capacitors when I bought it.
I wouldn't recommend it though.
I did this as a newbee myself and received significant help from people on this forum. The result of the effort was a ton of fun and two sets of rebuilt coils. I saved no money on rebuilding my own but what i learned and the sense of accomplishment was priceless.
I sent you a pm and will gladly share what I learned, as others here are doing.
all the best,
Andy, make sure you replace the capacitors w/the proper ones or sooner or later you'll be re-doing it.
I have unpotted probably well over 1500 T coils and the assortment of things one finds inside is amusing. Generally when a correct capacitor is replaced with something incorrect it is sort of capacitor looking device such as a diode, diode-capacitor combo, resistors, resistors+capacitors, very large electrolytic capacitors, metal jacketed capacitors with bare wire simply wrapped around the outside to attempt a connection... the list is long. For awhile I was saving them to make a display but decided against it. What is interesting is that most often these were found in coils marked "BAD" or "DEFECTIVE" on the outside but actually were just fine when all was corrected. The most interesting one had a skull and crossbones on the outside as the insignia of evil I guess. T mechanics do have a sense of humor.
What have you seen for potting material, John? I have done nowhere nears as many as you, but I have never run into anything other than tar. I have seen folks say they used silicone, but I've never had to work behind them. I could believe epoxy might be used, but then again, maybe not. No T guy would spend that much money. I can safely say that if I ran into silicone or epoxy, I would probably throw it into the scrap pile. I don't think I would spend the time it would take to dig either of those out.
In 25 years and over 17,000 coils rebuilt I have found sand, gravel, rocks, newspaper, epoxy resin, paraffin, body putty, body sound deadening putty, silicone and expanding foam inside coils.
Here is a photo of the capacitors removed from previously worked on coils.
Ron the Coilman
Expanding foam is another one I had heard of, but had forgotten about.
I wonder why people are so opposed to using tar? Two reasons come to mind. They don't have access to additional tar to fill the space left over from removing a large condenser and replacing it with a small one. Or, they think it is too much trouble. Using a small block of wood can solve the first one. The second one is just a mental thing. It is nowhere near as big deal as some imagine.
Hi all ;
What is the max. temperature when you repotting the coils . So that you don't damage your new capacitors. I always use 130 C = 266 F.
Thanks in advance
When it flows it goes.
Just keep the tar below its flash point - it will be fine.
I generally don't mess with coils that have had some sort of filler other than tar. The exception might be if filler is something that comes all the way out in one "blob". Remember that I am after the winding and generally just nip the capacitor and toss it away while the total tar from inside the box is evacuated. I then remove the winding and run it through a bunch of tests to make sure it is totally good and then install it in a new box with new capacitor and all new hardware. I then pot the whole thing. I melt my tar in a large coffee can formed into a pouring spout on one side with long handled pliers as the handle. I heat it over a single burner Coleman camp stove. Nothing else heats it as fast. I start pouring just as soon as there is enough molten tar in the can to fill a coil box since the liquid tar will pour out when there are still chunks of solid tar in the bottom of the can if you use the deep coffee can. In the same way that ice cubes in a glass of water kinda stabilizes the temperature of the water, I find that solid chunks of tar stabilizes the tar at a lower temperature since soon after all tar in the can is melted it will begin to smoke. If the tar is smoking then it is hotter than it needs to be and will splatter more as you pour it. I just add tar chips to the can as I go and then fill as many coil boxes as I can with the tar in the car that is melted then soon after adding more tar. I usually pour about a dozen coils at a time and will do about 6 batches (72 coils) in a day. Angela does the wiring and gets them ready for a "pour" and then she finishes them up after they have cooled. I just don't want her around the hot tar. I wear long sleeved shirt and heavy gloves just in case but it really isn't too bad unless you let the tar get totally melted and very hot and then the whole neighborhood stinks. The melted tar is barely 300F and I do check it with my laser temp gun and let it cool a bit if hotter than 300. Typical tar can flash over when it gets over 375 degrees F but it will be smoking pretty heavy by that temp too. Pour before that and be very very careful. There is nothing that works better since it drives out all moisture and holds all parts in firm position with just enough "give" to not make it all brittle. I don't reuse any of the tar that I melt out because I don't want to have to keep track of the low melting point tar versus the high melting point stuff. The new tar is higher yet than either of the 2 types that Ford used.