When rebuilding model t ford coils on a regular basis it can sometimes be challenging to find additional tar for repotting after change of capacitor. The solution of course is to become captain of a tanker that carries tar and pitch. Here is today's catch from the pump room!
I believe black RTV silicone is non conductive and may work equally as well.
Epoxy would work but you would never dig it out again.
That looks nasty.
Can't we just reuse the tar already in our coils?
No silicone in my coils. Yes I am reusing the original tar, but usually the new capacitor takes up less space than the old one, so there is a constant need for additional tar. The brown colour is not from the tar itself, it is from the absorbant powder used on the pump room floor.
I don't try to fill the space left open by a new cap. with tar. I fill that space with small wood bits. I've never had the need to buy tar and even have some left over. The best way I've found is to break the narrow side of the box loose with a scraper (opposite side of the contacts) and remove it. Plenty of work room and the glass insulator is left in place also. Done 25+ so far.
Does that pump room floor tar have a high enough melting point for use in T coils?
Tar joints in the road are great for this. just keep an eye out for traffic.
The tar that has been identified as the closest to the original tar is Type III Steep Roofing Tar.
Here's a properties sheet for type I-IV roofing asphalts: http://www.owenscorning.com/networkshare/asphalt/10009927-d-trulo-lo-odor-data-s heet.pdf I like the Owens-Corning low odor type III for repotting coils, I could get away with pouring it in the kitchen, there is very little sulfur smell. Type III softens at 185-205F, and from my experience can be poured @ 275F. Roof hot mop application temps are not to exceed 385F, Flash temp is 575F for all four types of roofing asphalt. jb
No silicon in my coils .....
What, we have a tar snob now ?
Silicone is a poor choice for use in re-potting rebuilt Model T Ford ignition coils.
Silicone based products contain acids that can damage capacitors, wire and solder joints over the long run.
Usually I buy extra bad coils and use the tar from them 15million car x4 coils each not counting aftermarket ones
My doctor said I wasn't getting enough tar and suggested I start smoking.
Besides what Ron said, that silicon is really nasty s#*t when you have to remove it later!
Do NOT routinely re-use tar if your coils are going into a 26/27 coil box (mounted on motor) since the earlier Ford tar has a way lower melting point and you will get seepage of tar from coils due to additional heat from the 26/27 coil box. This can make a real mess inside your motor mounted coil box. You can use a 26/27 coil in anything earlier but not vice versa. The earlier tar is easy to spot. If the tar is gummy it is most likely the later stuff. If the tar is really easy to get out of a coil and falls away in large chunks leaving the coil winding nice and clean - THAT is the low melting point stuff and you best not use it in a coil for a 26/27 coil box. Don't use that early coil in a 26/27 box unless you replace all of the tar. The type 3 steep roof tar is higher melting point than even the Ford tar used in 26/27 and on Fordson tractors which all need to have the highest melting point stuff.
Hope this helps.
How is it possible to recognize a coil that it is the improved style with the higher temp '26/'27 tar inside?
The higher temp melting point tar started earlier than 26/27. Coils marked "tractor unit" were the first Ford coils that had a higher melting point tar. Very soon after that Ford decided to use this higher melting point tar in ALL coils so the tractors then used the same coils as other cars and there were no coils then marked "tractor unit" after that. The only place where the higher melting point tar is critical to the application is Fordson Tractors and 26/27 Ford cars. I do not know of any way to spot the higher melting point tar by looking at the outside of the Ford coil. I can for sure spot the low melting point stuff by how easy it crumbles out of a Ford coil unit but that is not visible from the outside. Sorry I can't be more help but I don't rebuild coils, I re-manufacture them using all new tar which has the much higher melting point than did even the Ford original "tractor unit" but that is not to infer that the later Ford tar is not good enough - it is. I just don't have access to any lower melting point stuff nor do I seek it.
From other threads I can see that "tractor unit" coils were only used for the early production of Fordsons, maybe 1917-19?
Then there would be a very low risk to find any coils that doesn't fit a '26/'27 over here, since the vast majority of T's were sold 1919 - 27 here due to ww1 shipping restrictions.
The melting point of the pitch we carry ranges from about 150 to 280 degrees F. The pitch I recovered from the pump room has a melting point of about 210 degrees F. Should be good enough for a model T coil, I believe.
John, I've always heard Fordson coils were different, but no one could say why other than they were marked. thanks for the info.
You can get non-acetic silicone caulk that doesn't have the corrosion problem. Here's an example, although you can't buy from this source without a wholesale account. http://www.crlaurence.com/crlapps/showline/offerpage.aspx?Productid=1127&GroupID =589&History=39324:330:512:528&ModelID=589
OTOH, I've seen caulk - can't remember exactly what type - that is not really a good insulator. Tried to use something one time to waterproof a power connector on a camping trailer. It leaked enough current to trip a ground fault breaker.
Probably best to just stick with tar.
As mentioned above, Type 3 steep roofing tar seems to work well for re-potting rebuilt coils. If I remember correctly a 50 lb bag cost me around $24.
P.S. My Rachael Rey copper bottom sauce pan was not sourced from the kitchen.
The problem for Roger, Lorentz and myself is, the EU have limited the acces to tar of the types you mention here (based on crude oil) so you have to have some sort of professional scale of usage (like road construction) in order get it.
Wood tar can be bought as it is used in traditional boad building (for making them tight) but that tar has a much lower melting point.
Michael! Kom til Nyborg og få beg fra pumperommet du og!