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I’ve a strange phenomenon with my Model B that involves slight electrical arcs between the coils cases to the firewall. This obviously affects the runability, but even moreso it’s a hazard that I’d like to rectify before the engine can be properly tuned and the car driven on the road. The engine starts fine, but anything much below 850 RPMs and it doesn’t run for long. Presuming its a dead short or ground issue along the wiring harness somewhere, I’ve used new wiring to connect the battery to the starting lug, and from there to the Hershey switch. (I will be doing a full rewire of the car over winter with a Rhode Island harness).
So, the car is truly running on battery ignition with nothing else connected. I’ve also disconnected the wiring at the generator. The Hershey ignition switch seems to function just fine, but I noticed that it was connected to an old 6V Stewart-Warner “thumper” pump in the past, and hope that didn’t draw too much through the switch. A 6V Carter rotary is now in place of the old S-W, and that’s fused on a separate circuit/switch. All of the ignition components are new. Coils, points, condensers, wiring to the distributor terminals, as well as new plug leads, a NOS rotor and a dual coils Studebaker cap.
Given all of this, I’m wondering what other items I should address to track down and eliminate the errant arcing? Thanks for any suggestions!
Carl,
I am a little confused (a common thing), are you actually seeing an arc from the coil case to the firewall? To me this says a breakdown inside the coils. Can you clarify? Dave
Thanks for inquiring…
The arc is occurring between the coil case and the firewall, and this is happening with the originals as well as the Brillman replacment coils. Both sets are just resting in the firewall holes, and not bolted in (this is especially the case for the Brillmans that don’t have a mounting flange).
After doing some more troubleshooting, I suspect the spark leakage is moving from the distributor + terminals and back to the coils. Both show ground to the block.
Have you replaced the secondary wires from the coils to the distributor? How about the rotor and cap? Electricity is going to take the path of least resistance, so if one of those has high resistance it might cause the spark to take a different path through the coil case. I have a hard time visualizing spark feeding back through the dist/coil primary wire, but I guess with some fault in the distributor it might. Dave
Yes. All new wiring, including the plug leads and secondaries, NOS dual ignition Studebaker cap, NOS rotor, points and condensers. I’ve also run the car on the original coils and the new Brillmans. The arcing is slight, but bridges the gap between the coil cases and the firewall…it is not jumping the terminals or forming carbon streaks that I can tell. Anything below, say, 850 RPMs and the car doesn’t run long, probably given all the extra fireworks. Hard to pull coil secondary wires and tune the carburetor properly in this state!
It sounds like you covered things. What is your feeling about the arc, a high voltage arc, or a 12v arc? What is the arc length? By “Both show ground to the block”, you mean the coils show no voltage potential to the block ground? How about between the block and the chassis? I can’t see how the coil cases would have voltage potential to arc to the firewall if they are at ground. Perhaps I am misunderstanding something. I am hoping someone else will chime in with some ideas.
The voltage is reddish-white and faint, but enough to interrupt the individual plug firings and contribute to RPM fluctuations, as noted on my timing light. I suspect I may have a crossfire situation going on in the metal loom. I removed the distributor head and spun it on my Sun to confirm the proper timing, and again timed it to the engine. Will now use the original Delco cap and fresh leads to do a quick diagnosis and rule out the crossover possibility within the loom, or a bad cap (I’m not using the existing leads, but a new cloth-covered set I made up, so I can latch the cap and get to testing).
Thanks again for the interest and advice…
Made some adjustments to the distributor and replaced the coil secondary leads today, but still have the same issue with the arcing. I temped-up a new switch, and wired the coils directly to the battery to isolate the ignition circuit. The generator is also disconnected at this time. As you can see the arcing is affecting the idle. My next step will be replacing the plugs and individual leads, as there may be a crossover in the loom.
Again, thanks for any suggestions!
Looks like those coils use the flange as a grounding point to the firewall/chassis. Have been chasing my tail with new coils that don’t have the flange, and therefore the ground. Hard to beat the old Delco-Remy originals, I guess. (Now for the speedo repair and the full chassis rewire this winter.)