Technical grounding distributor

While my hot rod was comfortably idling ( 324 Olds with an aluminum housing W&H ducoil distributor) I connected a jumper wire to the engine block & scratched the wire against the dist. hsg. small blue sparks appeared ! This of course indicated a poor ground at the dist. The engine was running perfectly. I ran a permanent wire to the block. My son says his IMCA friends always ground their HEI dists externally. I'm 81 & still learning. speedshifter Greg White

 

That makes sense, I will have to try the spark test and see if mine are needing better grounds.

 

Yep, battery to frame, engine, body, truck bed, radiator, distributor, alternator, and lots of redundant grounds for lighting and other elect. equipment. It makes a difference, especially on our old heaps.

 

It may be a high tension (secondary voltage) leak. Try it with the engine not running, but the ignition on. Make sure the poinjts are closed.

 

I usually tap a hole in the distributor body and with a wire, ground it to the same spot on the firewall as the coil. Nobody ever had a problem with too many grounds.

 

This may or may not be the case, but I remember reading once that the hold down clamp was supposed to form a ground to the block (and then block to frame etc.) This was in the context of paint and so on potentially causing a connection problem.

 

I think some of the PerTronix ign. problems could be helped with this idea.

 

After a Pertronix failure is when I started doing this.

 

There is an excessive resistance test, to be measured between the distributor points plate and the battery ground post, it's important regardless whether running Ignitor or contact points. Should not exceed 0.2 ohms, the resistance of the meter leads need to be subtracted for accurate measurement.

 

Any time you need an accurate resistance measurment of less than a few ohms you should do a four wire measurment (a.k.a. Kelvin), where you use a separate source to run a known current through what you want to measure, and then you measure the voltage drop across it. Very accurate as the resistance in the meter wires etc. doesn't matter, you just need to know the current going through it all and the voltage across the interesting bits, and calculate resistance using ohms law (R=V/A).

 

Interesting. Smokey Yunick always recommended an external ground to the distributor.

 

You could just connect a volt meter between the battery ground post and the distributor base with the engine running. Ideally it should read zero volts or very close to zero. That is a pretty accurate way to test 12 volt automotive circuits.

 

Driver50X I am familiar with the low voltage test. I considered making thar test but I was lazy& the spark test was good enough for me. Greg