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Hi guys. My truck has been running great until a couple of weeks ago. Then it was temperamental to start, and it had developed a skip. Last week it went from running ok, to totally dead in one second. It just died, and would not even try to start. I was uphill of my house, so I coasted home fortunately. Upon pulling the #1 plug and testing for spark, I found no spark. I had also put two brand new Optima red tops in it a couple of days earlier. That really helped the hard starting.

I pulled the distributor. The coil in it read 6.4 ohms on primary and 10.72 K-ohms secondary. The secondary seems low
I have another coil. It reads 4.3 ohms primary and 14.18 K-ohms secondary. Primary seems low. Both coils seem old and are molded "made in USA" on the top. What do you think of these numbers? Two junk coils? If there is any doubt I will buy another. Its not worth the hassle to me to try questionable parts. All vent lines and fittings in the carb throat are correct and installed

What is the consensus on the replacement coils? $60 one made in Turkey, or the NOS $120 coil? The rotor also had a little cone of debris on the top/center of it. I don't think that was an issue, but the center contact seemed a little bit carboned up.

I've read that some of the replacements are just a bit shorter and don't contact the bottom of the housing, so they can't sink heat through the case and overheat quickly

This was posted by Sal a while ago, good info.

download/file.php?id=1906

Carter, In that picture, shouldn't there be a reading from terminal A to B?

Isaac, knowing that, I'd guess I could make an appropriate thickness aluminum spacer to go under the capacitor. Thanks for the heads up

A > B reads 0.5 to 1.0 Ohms according to the photo, lower right corner.

Hi Guys,

Carter, great pic........thanks! For coils that are out of the distributor the way I remember how to check resistance is;

Primary: "Positive (+) Terminal" to "Negative (-) Terminal"
Secondary: "Center Tower" to "Negative (-) Terminal

To muddy the waters a bit........you can also check the secondary resistance by measuring from the Center Tower to the Positive (+) Terminal. Done this way you're adding in the resistance of the primary coil, but it's so low compared to the Secondary resistance that it doesn't affect the reading. You might also want to turn the coil upside down while you're checking it to make sure it's still sealed. If oil leaks out the center tower it's junk, no matter what the resistance is.

regards,
bob

Are you guys sure about those primary ohm readings? I read a lot of searches about it on this site and I never saw .5 to 1 ohm for a primary resistance. More like 6 to 12 ohms. I was reading them like the downloaded picture showed, but out of the distributor. I think I will order a couple of new coils, or NOS.

Is there any negative to NOS coils? Do any components inside (insulators) degrade over time? Are coils made with todays components better, or more robust. from reading many posts, and from looking at NOS coil prices, it seems like the old ones are preferred.

One other thing. I don't run a truck radio of any sort. Is there any reason to keep the radio filter in the distributor? I am assuming cell phones are not affected by the interference of the old truck.

A couple years ago I had a problem with the coil feed wire arcing out inside the distributor housing. Due to the heat the insulation became dry and cracked. after replacing the feed wire the problem went away.

ZGjethro wrote:Are you guys sure about those primary ohm readings? I read a lot of searches about it on this site and I never saw .5 to 1 ohm for a primary resistance. More like 6 to 12 ohms.

I would have to go through my old notes to verify those readings and as stated I copied the pic from what Sal posted.

After checking I located this, more believable I am sure:
On the primary side you should have 6 Ohms, on the secondary side you should have 14.5--15k Ohms.

Thanks Carter. I didn't think 1 ohm seemed right. neither of the two coils I have fall in the desired range, so I think I will order new ones.

Edit. In doing some internet searching, Is our coil shared by some other military vehicles? Also, the chromed ones from china with no markings on them seem to be universally despised. I'm searching for NOS units now

I found NOS coils on VPW for $120. Ouch! I have one coming, along with several hundred dollars in random parts.

Hi Guys,

I did a little searching around on the web and it seems no one really knows what the primary resistance for the 24V coil is supposed to be. My notes say 6 ohm, but I don't know where I got that from, so it's suspect. The 0.5 to 2 ohm numbers seems to be standard for 12V automotive coils, so doubling or tripling that number for a 24V system would make sense to keep the current low in the primary. But like I said..........I haven't seen it printed anywhere yet.

As for coils, I believe the first repop coils were made in Turkey......and weren't too reliable. The newer ones I think come from our friends in China.......and haven't been that well received. I don't know if the primary resistance of the NOS coils, those made in Turkey, and those made in China all have the same primary resistance. If anyone knows for sure......or knows where in the TMs it calls out the primary and secondary resistance values for the original Auto-Lite coils, please post it. If I get some time later I'll do a bit of digging on my own and see what I come up with. We need to get this sorted once and for all.

regards,
bob

Thanks for doing some checking on this Bob. I had done a lot of searching and had come up with conflicting numbers, usually for the primary side resistance. It seems like 6 ohms is about right for the primary.

I have a NOS coil coming. It is kind of a crapshoot though. I don't know if it is a decent piece, or if it is as old as my 52 truck, with dried out and cracked internal insulation. it is really unfortunate that we don't have access to quality new coils

I got my NOS coil from VPW and it was perfect, no issues at all.