24 volt coil question

[Longhunter7]

Gentlemen,

Does anyone know how to test the original 24 volt coil for the 230 c.i. engine? What ohm reading should I get with a meter?

[w30bob]

Hi Long,

Well.....here's what was said on here awhile back by CUZ;

"First of all a digital VOM is needed for best, most reliable and accurate readings. You are looking for .5 to 1.0 Ohms across the primary coil. Zero indicates the primary coil is shorted. Infinity or open means the coil has a broken wire. The secondary will ohm out anywhere from 14,000 to 20,000 ohms."

regards.
bob

[Longhunter7]

The reading I get across the coil, is 6.6 on a digital meter. Does that idicate a good coil?

[w30bob]

Hi long,

Now you're putting me on the spot. Sounds high, but I'll check one of my coils when I get home tonight and see what I get. I don't have any experience with these coils, I just cut and pasted that info from CUZ's post.

regards,
bob

[hbb]

Long,
That is a very good ohm reading for a coil, If you were to check 10 new coils that would be a constant average.
hb

[Longhunter7]

Gentlemen,

Thank you for the assistance! Now I can eliminate the coil from my ignition problem.

[w30bob]

Long,

That's only the primary side of the coil.....what about the secondary side? Did that test good?

bob

[Longhunter7]

I guess I didn't make it clear that the 6.6 reading on the digital meter was across the coil + to - .

[w30bob]

Hi long,

No, I got that.....but the ignition coil is really two coils of wire inside the can. The difference in the number of turns of the coils determines the stepped-up output voltage. The primary side is what you measure by putting the leads on the (+) and (-) terminals. That's the side that sees the 24V from the voltage regulator. The secondary side is the voltage delivered to the spark plugs via the points. So in an ignition coil either of the primary or secondary coils can be bad and it won't work.

To measure the secondary side you put the (+) lead from your digital multimeter in the top center of the coil (at the center of the two raised circles) and you connect your (-) lead to the (-) terminal on the coil. Per CUZ that resistance should be between 14 thousand and 20 thousand ohms.


ignitioncoil by w30bob, on Flickr

regards,
bob

[bill monahan]

I recall with my M151A1 a few years ago coils were becoming hard to come by. Only ones I found were Chinese and really crap. Had to return two, vehicle wouldn't even start. Chrome plated to boot. I assume these are the same coils for the M-37?

[majorhitt]

Hello, I had an issue with my M37, and the coil was one item I expected to be the culprit. I did a bit of research and found that for the 24v coil you should see 6 ohms on the Primary and 14.5-- 15k ohms on the secondary. This info eliminated the coil as an issue with my M. And Bob nice cartoon there.

[w30bob]

Only the BEST for you guys!!

regards,
bob

[jimmy_stikx]

Have you tried replacing the condenser? My dad had a nova that the mechanical regulator went out on and as the alternator got up to 24 volts to the system would burn out the codensor. Everything else was fine.

[mylo219]

got me a 1952 dodge m37..dont get no spark at all so am replacing distributor inners with the pertronix M-161A spark ignitor, they say I need a coil with a minimum 6.0 ohm.... what and where to get what I need....getten despert here...Mylo

[arkadd61]

Quick follow up question to this thread. If my multimeter is only pulling about 10.5K ohms on the secondary does this mean the coil is probably shot? I'm pulling 5.9-6.0 on the primary.

It's definitely not getting a spark at the #1 plug. Hoping by listening to the engine turn over someone might be able to help diagnose I've included a link to my youtube channel of me turning over the engine and videoing the #1 plug wire not sparking:
https://youtube.com/shorts/IbPRx4oMku8?feature=share