Coil Box Woes

[Oldav8tor]

A friend has a 1920 Roadster that he has spent the past year getting into good running condition. Back in May he took it on a tour that encountered heavy rain. From that point, the car just wasn't running right. He assumed the coil box got wet causing problems and dried it with a hair dryer. It ran better but still not great. We convened some of the "guys" and started checking out the possible culprits. The main symptom, cylinder # 1 & 4 had spark but the spark was weak....very weak.

Our "A" team, Brian and Tony, decided to remove the coil box and give it a real close look. First, the wood had been replaced with home made plywood pieces - not the best grade of plywood I might add. What they found was that the high voltage contacts on coils 1 & 4 had arced and formed a carbon track from the contacts along one of the plies to the frame of the coil box. The carbon tracks did not produce a complete short but directed a portion of the current to ground. The fix - we replaced the wood box parts with a plastic kit from Snyders.

Looking at these pix the carbon trails really stand out.

[TWrenn]

The plastic replacement kit is a no brainer.

[Russ T Fender]

I did the plastic kit on my '27 and it came out well but the coils are so tight in the box I can barely get them in and out.

[TXGOAT2]

Low grade plywood with voids is not suited for for coil boxes. Many other types of plywood can absorb enough moisture to allow current leakage. A quality marine grade plywood might do a fair job, but the best course is to use the "plastic" material.

[Norman Kling]

I have the plastic one on a 26. It shows whereas yours is behind the firewall where it does not show. These are made to look like wood and to most eyes, it looks like an original. I would recommend it. If you use wood, try not to take it out in the rain and avoid hosing down the car especially around the firewall.
Norm

[Oldav8tor]

Plastic coil box replacement kits are a no-brainer for someone with experience. To the new Model T owner the symptoms a shorted coil box produces can leave them totally flumoxed. I would recommend to any new owner that they be proactive and rebuild the coil box if it hasn't already been done. Two things to remember - once the carbon track is formed it's there to stay unless you can find some way to remove it. Just drying the wood will not do the job. Carbon is not as good a conductor as copper wires so you end up getting a divided current path. Some goes to the spark plug (weakly) and some grounds to the box. From there it seeks a ground, sometimes thru the fingers of the Model T owner. My friend had a steel firewall so it found an easy ground. The symptoms of a shorted coil box can be very perplexing but once you've seen them you'll remember.

I was lucky to get one of the last of the John Regan engineered plastic coil box kits back in 2019. The current plastic kits need a little extra work to fit everything together. A few suggestions - use your original phosphor-bronze contacts if you have them...they are superior to the available reproductions. If you have a problem of your contacts losing their "spring" and making poor contact, double them up. I and a few friends have tried that with great success. For example, you can back up an original contact with one of the repops for added strength. I also solder the contact to the bolt head to insure a good connection.

Sometimes the coils fit pretty tight in a rebuilt box. Ron Patterson (the coilman) recommends getting some paraffin wax (used for canning) at the grocery store and working it into the wood. Clean any wax off the contacts with lacquer thinner. If your wood has bumps or high spots you can carefully sand them down but the wax should do the trick in most cases.