12V Model A lost spark

F

fried okra

Senior Member
My 12V negative ground 1931 Tudor lost spark while hot idling in my drive. It had been a reliable touring car for years before I bought it.

It was running great, but shut down suddenly while idling. I've pulled plug leads and used a new plug to ground but have lost spark while cranking.

I am running a modern upper plate and points looks like with a wireless NuRex lower plate. Points are clean and gapped at .020.

My skills are more mechanical than electrical.

All thoughts and suggestions are appreciated.

Thx!
 
Make sure the high tension lead from the coil to the distributor is fully inserted, both ends. Try a different, known good, coil. Turn the engine over until the points are open or insert a piece of paper in them as an insulator. Turn on the ignition and measure the voltage at the moving point. It should equal your battery voltage. If not, look for an open circuit, like the ignition switch or ammeter. Follow the voltage from the battery to determine where you are loosing the voltage. One place to test is at the junction box on the firewall. If you have a fuse, check to see if there is voltage on both sides, it may be burned out. If it is burned out then you may have a short somewhere.

If you get frustrated, take a break and fry up some okra.
 
Check the contact between the upper and lower plate. The wireless
plates are a known trouble area.
 
Get yourself a Sparklite tool. It plugs in between the top cap and the high tension lead from the coil. Spark is quickly evident and polarity can be checked. Nu-Rex also makes a C-Lite tool that is a regular spark check tool similar to the Sparklite.

I always carry a new condenser in case it craps out due to the heat. Model As have always been sensitive to condenser failure. The spark really craps out if the condensed dies. Coils usually crap out after a person accidentally leaves the ignition key on and the points happen to be closed. I still purchase the Echlin brand condensers for the new style plates. A&L condensers are the way to go for original type plates.
 
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Loosen your gas cap as a 1 second starting point and try again.

Our coupe lost power out in the countryside a year ago. I felt it die as I pushed in the clutch approaching an intersection. My eyes go straight to the ammeter when that happens.

The ammeter went to zero. After coasting to a stop half off the road, I touched the starter. The starter cranked normally, but there was no Henry Jiggle in the ammeter as it did so. (Service Bulletin wiring change, all Model A's, November 1929, page 390)

Our horn works good. I tried the horn, no horn. I turned on the lights, we drive at night some. I got out checked the lights. (it was a sunny afternoon) No lights.

Hmm. I headed for the safety fuse. I had been suspicious of it since we bought the car. It was so flimsy, especially at its riveted ends. I wiggled them and the lights came on. We started the car and headed the ole girl for the barn.

Removed the safety fuse and installed a modern, enclosed fuse and camouflaged it with loom. No more problems....as yet. Several thousand miles tho.

Many times, the ammeter and the Henry Jiggle that it displays is your first best friend.
 
Good input group.....I've got a spare "stock" distributor with side mounted condenser under the top plate (my terminology) that came with the car.

I can swap it out as a test without needing to reset the timing I think?
 
Before you start swapping things out, do some investigation with your volt meter. As Rob suggested it may be something simple like a fuse.
 
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The modern set-up you have has a slider that connects the two plates, it is not a good connection. As it slides it sparks and wears a burn path, mostly at the idle position and the cruise position. After about 1,000 miles the connection deteriorates and then fails. Your best bet is to have a wire connecting the two plates. It is important that the wire be a multistrand wire so it can move with the actuation of the spark advance.

Tom Endy
 
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