My dad has a 1927 tt truck. We are having problems with spark on #4 cylinder. The plug has little or no spark. It has to be pinched almost all of the way closed to get some spark. I have switched coils, plugs, wires, and checked the cap and rotor. Even when I take the plug wire and grnd it I get minimal spark. The coil seems to be getting plenty of electric and buzzes well just like the others. All of the rest fire just fine. It does the same thing on batt or mag. I do not see any burn marks in the coil box or on the ceramic insolators where it is shorting out. Any help would be appreciated.
It is most likely carbon tracks in the laminated wood of the coil box shorting to ground.
Rebuild the coil box with a FunProjects coil box wood replacement kit and I suspect your problem will be solved.
Ron the Coilman
Not sure how a cap and rotor mix with 4 coils since those are parts from 2 different systems. I shall assume you mean the timer and the brush inside. To localize the problem. Pull the plug wire at #4 and hold the wire near ground with something other than you hand. Turn the ignition on bat and if any coil is buzzing, turn the engine over a bit till you stop at a spot with nothing buzzing. Now put a jumper wire from the top connection on coil #4 insulator (at the firewall engine side) directly to a good ground on the motor and that should cause coil #4 to buzz continually. If the spark is still weak then the problem has nothing to do with the timer and brush and the problem is in the coil box and/or coils. If the spark is now strong then the problem is with the timer/brush/timer wiring. Make sure your plug wires are SOLID WIRE conductor types and NOT the carbon filled modern wire types since those can spell doom for your coils or coil box and can cause this type of problem and others too. It sounds like you have High Voltage leaking likely due to a breakdown or arcing within the coil box wood going to #4 spark connection at the box. You can try this late at night in a dark garage and look for any sparking other than at the plug wire you have held near ground. Often there is arcing within the wood that makes up the coil box lining at the back or bottom of the coil box. Since the problem is confined to #4 and you have tried other coils there that work fine in other positions in the coil box - that is about all it could be. If the coil connections inside the box that go to #4 are marginal - that too might cause this but I think it is High Voltage leakage within the wood. Hope this helps.
First thing I would do is switch the coil with another coil and see if the problem goes with the coil or stays with #4. Or you can switch your coil with another from another T and see how it runs, and see if that cures your problem. If so, your problem is in the coil itself. If not, it is either in the coil box or the timer. Sometimes the coil doesn't make good contact with the inside of the coil box. If you push the coil down and forward with a popsicle stick or other wedge, and it works better, you have a problem with the contacts inside the coil box. You could also have a problem with the timer being off center causing it to skip #4. Having said all that, I would think the problem to be either the coil itself or the wood in the coil box since you are getting a weak spark, some of your spark is leaking off, most likely through the wood.
For the longest time I was convinced that I just had something loose as banging things about, jiggling this and that etc., seemed to always getting me where I was going and coming from. Finally I concluded that others, like the guys above, were right...Whether I had a leak through the wood coil box liner or not...I was going to swap it out for one of the FunProject non-conducting shell boxes.
Actually, I learned my lesson simply by taking the coil box off of the firewall. It had green stripes on the laminated wood and even though I'm dumb on electrical, I knew enough that green and electricity don't mix! Did the rebuild in the course of an afternoon, and had a 10 fold improvement [to me] in ignition.
I've been there too when my T got really wet in a
rainstorm. It would run alright for a little while
but once you got past a certain rpm's it seemed, it
would start to run on just three cylinders. Got the
coilbox rebuild kit and it runs good again. I could see the carbon trail radiating from a couple of the terminals.
Trouble shooting a previously wet Model T coil box and the resultant elusive carbon tracks is something you never forget. The next time you see the symptoms you recognize it immedaitely.
Ron the Coilman
Are the knurled terminal nuts a recent acquisistion? Where did you get them? The ones I find these days have a coarse straight knurl.
Was that coil box re-build on the '15 Runabout ?
The knurled nuts were original to the original coil box set.
Yup, was on it when you stopped over last time. I did the change over summer of 08
The nuts with the criss-cross knurl are available in 8-32 thread from Restoration Supply Company http://www.restorationstuff.com/index.htm . See page 3 of the catalog.
Other sizes only come in the straight cut knurl.