Distributor issue

Dick M

Dick M

Well-known member
My spare distributor is completely rebuilt and the last time I ran it was 2018 for all of 50 miles. I installed my spare distributor yesterday and found I had no spark. I removed the distributor and replaced the condenser, still no spark. I had power from the lower plate to the points. However, when I turned the engine over with the key on, no spark from the coil wire to a head stud. I bench tested it using an multi-meter ohm function. I had continuity from the lower plate to the points. I did not detect any short to the body or upper plate. The bottom of the distributor is clean as is the head mating surface. I also engaged the set screw so the ground should be good. My car starts right up when using my other distributor. Any ideas of what I am missing?
 
X2 on post #2.

Key on, points propped open with the cardboard from post #2 and using your Voltmeter, set on the 10 volt scale, what is the voltage at the tip of the points arm?
 
Possibly something to do with the armored cable and how it’s connecting inside the distributor. The replacement lower plates can cause it to short out. Something to do with the fiber washer that often gets left out.
 
Chuck,
I have power to the points. I do not have continuity from the hot points to the distributor body. I think that eliminates a short from the plug being too far in. I have also checked for a good ground by using the ohm meter from the distributor body to a head stud and it shows 0 resistance. I am stumped...
 
Last year I bought five condensers from one of the vendors. The first two didn’t work but the third one did. Several months later when I bought one of those $20.00 capacitor testers, I checked the two condenser that failed, and both tested bad. The other two tested good though and carry them for spares.
 
Dick, with key on, manually open and close the points. I use a small wooden stick. do you get a spark?


If not, are the points actually closing? Rotor is turning when cranked? Check point gap?


if you do, you can isolate the coil and high tension wire for a test by unhooking the red + coil post wire and replacing it with a jumper. You can touch the opposite end of the jumper to a head nut or other clean ground manually and generate a spark in the high tension cable. Take the high tension cable out of the distributor and place it 1/8 - 1/4" from a clean head nut. You are replacing the actions of the cam and points to test just the coil and high tension lead.

If coil and tension lead are sparking good, look at the dist. cap, rotor, body etc. If your other distributor had no problems, I expect the coil and its high tension lead to be good.

If coil and tension lead are not sparking good, did you leave the key on and damage the coil? You can test it with the ohmmeter. Substitute a different coil wire.
 
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Dick, with key on, manually open and close the points. I use a small wooden stick. do you get a spark? Rob Doe

If you don't get a spark, try replacing the points and try it again. I have had several sets of points go bad on cars that sit for a year or more.
 
Ok...This is a real teaser. I turned on the key and opened and closed the points and saw a spark between the points and at the same time I saw a spark from the coil wire to the head stud. However, when I used the starter to turn the engine over, I had no spark at the coil wire to the head stud. I have even removed the condenser and tested again with the same result. I had spark when opening and closing the points manually but not when cranking with the starter. By the way, I put my good distributor back in and had spark at the head stud. So, I have isolated the problem to the backup distributor but I do not have an answer...Grrrr.
 
Wild guess, I had a similar problem and it was low battery. I guess the starter turning over reduced overall voltage loss. Charged battery and it started right up.
 
It is possible you have screwed the armored cable too far into the distributor body and the isolated contact on the lower plate is making contact with the distributor body. With the disstributor installed check for continuity between the lower plate and the distributor body. The lower plate should be electrically isolated.
 
Quote: CT Jack: The lower plate should be electrically isolated.

CT, you meant the buss bar portion of the lower plate is electrically isolated, right?
 
Check to make sure there is no voltage to points when there are closed. I tend to think the points are still dirty.
 
Just recently my A was starting a little slower and at high rpm’s running rougher, I swiped some rough parts box cardboard through the points until no more black showed on the cardboard. She now starts instantly and no rough running at higher rpm’s!
 
Hello everyone,
I first want to thank all who responded. Believe me when I say I tried every suggested test without finding the problem.
So, good news/bad news: I went out to the garage this morning and completely took the distributor apart. I checked every electrical connection while wiggling the pigtail wire. I could find nothing amiss. I reassembled the distributor, reinstalled it, and reset the timing. I ran my usual coil wire to head stud test and found I had spark. I then went to start the car and it fired right up. So, the good news is the distributor works and the car runs and the bad news is I do not know why....
Perhaps the Model A Gods were with me today......
 
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