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M38 Spark Plugs
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Naugha
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Location: Ocala, Florida

PostPosted: Wed Aug 11, 2021 8:15 am    Post subject: Reply with quote

Now for the flip side: The spark plug wires

Last year before I knew that “For M38”, “Fits M38” we’re dubious terms, I bought a few things that are ..... well, dubious.

It would be nice if the plugs I eventually buy can use these cables.

2920-00-792-9777
FSCMn8N223
Cable Assembly
DAAJ09-82-C-DO75
C. 1/84

Four spark plug cables, all 18” long from elbow to elbow. (NOS?)
Each end has a little spring wire.
I will send pics later...... I will also do some Google work.




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Don Alvarez
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Naugha
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PostPosted: Fri Aug 13, 2021 10:26 am    Post subject: Reply with quote

Quote:
Ron D. “I'm using Autolite 295's”
.
A few questions & an Idea. 💡

*Do 295’s do well in a M38?..... 24V system.

*What other modern day plugs do M38 owners use?.... 24V system.

* At least one brand of adapter says you can use NOS type M38 plug wires with the modern day plug. How do they do that?

Plug adapters can be a choice in a world without proper plugs.
They are mostly cosmetic (which is fine) and usually pricy.

Now for a silly idea that could inspire someone who can make it work.

-Find a modern day M38 compatible plug with a small diameter & profile.
-Cut the threaded base off a burned out M38 military plug.
-bore out the old plug so that the it fits over the insulator of the new plug.
-solve the problem of how to fit your NOS M38 wires on the new plug
-use permatex & small locking screw to attach the shell of the old plug over the upper part of the new plug.

You would end up with a DIY adapter ‘cap’ & plug that looks like a slightly longer 2243 or ....... maybe some variation on this DIY would work.
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Don Alvarez
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keats
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PostPosted: Fri Aug 13, 2021 2:13 pm    Post subject: Reply with quote

champion J8 have been used in all my civilian jeeps with the L-head and the f-head without issue. J8C may be the modern version.

I remember a time I was having a carb issue on a m38 fouling the 2243 plugs. I used the waterproof cables by unscrewing the top piece of the j8 plug and putting the spring on the m38 cable over the threaded end. worked for as long as it took me to correct the carb issue.

perhaps not the best solution. maybe some sort of rubber boot over the connection for long term use.
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Gary Keating
1949 C3A, 1952 M38,
1954 M170, 1957 Cj3B
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RonD2
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PostPosted: Fri Aug 13, 2021 3:38 pm    Post subject: Reply with quote

Don,
While your plug wires might work on the M38, they obviously aren’t “correct” for a M38. From what I can determine, they belong on the M274 Mule. I didn’t try to find the Army TM ORD9 for the Mule to confirm it, but at least one vendor I found says they’re for the M274, here: https://www.easternsurplus.net/PartDetails/6807/MU-242-Spark-Wire-Cable-M274-Mule

The M38 plug wires are called out in the September 1955 ORD9 on page 147. The wire for plug #1 is 23-3/4 inches long, G740-7528173, and the wires for plugs #2, #3, and #4 are 19-3/4 inches long, G740-7528174. Your Mule wires are all 18 inches but would likely reach anyway.

We already discussed the pitfalls of buying old government surplus parts. Are the plug wires in your bag really what’s described on the label? Are the wires otherwise not defective government rejects that got sold on the civilian market?

According to the label, your wires were made in 1984, which makes them 37 years old. Assuming you intend to use them anyway, if the end connectors aren’t brittle or rotted and will hook up correctly, before using them I believe I’d test them for insulation resistance breakdown using a megohmmeter. I happen to have one (AN/PSM-25 Test Set, Insulation Breakdown), and most any old-school radio repair shop or HAM radio operator could also test them for you. Or, you could just hook them up and keep your fingers crossed. The first 6-8 pages here describe it pretty well: https://www.instrumart.com/assets/Megger-Guide-to-Insulation-Testing.pdf

Do you have a copy of Army TM9-8000, Principles of Automotive Vehicles? If not, I suggest you consider buying one and read Section 5 starting on page 196. You can buy a good copy most anytime on fleabay for about $20. Then you might understand your spark plug questions better.

Spark plugs are HIGH VOLTAGE components, input and output. They operate on KILO-VOLTS (thousands of volts), about 20,000 for the L134 motor. The spark plug gets HIGH VOLTAGE from the distributor that gets it from the ignition coil. The ignition coil is the component that takes a 24 volt (or 12 volt) input and increases it to 20,000 volts through the magic of induction. In other words, a spark plug has kilo-volts going in and kilo-volts going out ---- it doesn’t matter if your jeep has a 24-volt or a 12-volt electrical system.

Therefore, yes, the Autolite 295 plug works well on the M38. It’s the non-waterproof civilian equivalent to the waterproof military Autolite 2243. The Champion J8 (J8C) is also a good equivalent. There are others. When you go to the auto parts store and tell them you have a CJ3A, most can actually look them up for you. Naturally, you still have to trust, but verify.

Your question “At least one brand of adapter says you can use NOS type M38 plug wires with the modern day plug. How do they do that?” is entirely perplexing to me. What do you think the word “adapter” means? Have you seen these 3 photos that show it very clearly? https://store.midwestmilitary.com/product-p/mwm259.htm Or these photos?: https://www.ebay.com/itm/274426613655?hash=item3fe519cf97:g:DbIAAOSwbl9d6aBx

I think your self-described “silly idea” to cut, bore out, and glue up some DIY spark plugs is just that, laughable. What could go wrong with making your own HIGH VOLTAGE components? Shocked

The adapters aren't "mostly cosmetic", they're entirely functional. And they're a great example of American ingenuity. Yes, expensive. The price you pay (one time) for ingenuity. Or, you can try to corner the market on 2243's (consumable, throw away when worn, out of production) spark plugs for the same price as an adapter.
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Ron D.
1951 M38 Unknown Serial Number
1951 M100 Dunbar Kapple 01169903 dod 5-51

“The only good sports car that America ever made was the Jeep."
--- Enzo Ferrari

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RonD2
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PostPosted: Fri Aug 13, 2021 5:35 pm    Post subject: Reply with quote

One of my day-dreams besides winning the lottery is getting to the U.S. Patent Office first with something like these adapters.

Hula-Hoop, Slinky, and the great Sledge-O-Matic also top the list https://www.youtube.com/watch?v=ErppAlOIGQE

You're an animal Don! Laughing
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Ron D.
1951 M38 Unknown Serial Number
1951 M100 Dunbar Kapple 01169903 dod 5-51

“The only good sports car that America ever made was the Jeep."
--- Enzo Ferrari

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Naugha
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PostPosted: Fri Aug 13, 2021 5:49 pm    Post subject: Reply with quote

If the cables work I will use them. Errors unseen from the road, that can be rectified with an easy to install part, can wait for another day. I will, however, endeavor to stop making mistakes.
—————————————————————-

I have never examined a plug adapter but thought they are mostly a cosmetic shroud with some feature that connects the military cable to the top of a civilian plug...... no voltage modulation... just the physical connection.

Looks like they slide over the insulator part of the civilian plug, resting on the neck of the plug. The ads say they have a small screw on the side that secures the adapter (shroud) to the plug.

So OK, maybe there is a lot more going on here than M38 eye candy.

I was thinking about a gutted, modified, electrically dead military plug body (shroud) big enough to accept the upper part of a slender M38 substitute plug. Not engineering a new plug.

At least I now know about the ‘Great M38 Spark Plug Problem’ and possible solutions. You never know. It’s a big world with many dark drawers where four M38 plugs could be hiding.
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Don Alvarez
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Naugha
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PostPosted: Sat Aug 14, 2021 5:49 am    Post subject: Reply with quote

Quote:
I remember a time I was having a carb issue on a m38 fouling the 2243 plugs. I used the waterproof cables by unscrewing the top piece of the j8 plug and putting the spring on the m38 cable over the threaded end. worked for as long as it took me to correct the carb issue. perhaps not the best solution. maybe some sort of rubber boot over the connection for long term use. Gary Keating

Gary’s temporary fix sounds interesting. Maybe there IS a way to reliably connect the waterproof cables to the modern plugs without overly complex modifications.

A burned out military plug still has the threads up top for the M38 cable. If there is not enough space in the dead plug to insert a new plug top, then a short section of black pipe can be threaded.

Gentlemen, isn’t piddling around part of the hobby?
I think i’ll give it a go..... where is my hacksaw and duct tape ??
Will let you know what happens.

Gary, please keep thinking about how to make that stable plug-to-wire connection. Don
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Don Alvarez
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RonD2
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PostPosted: Sat Aug 14, 2021 5:56 am    Post subject: Reply with quote

Ok Bubba. There's always a better mouse-trap just around the corner. Laughing

The search button is your friend. Have you seen this? http://willysmjeeps.com/v2/modules.php?name=Forums&file=viewtopic&t=11268&highlight=plug+wires
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Ron D.
1951 M38 Unknown Serial Number
1951 M100 Dunbar Kapple 01169903 dod 5-51

“The only good sports car that America ever made was the Jeep."
--- Enzo Ferrari

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wesk
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PostPosted: Sat Aug 14, 2021 10:29 am    Post subject: Reply with quote

Nice choice RonD!

I took the liberty of editing and condensing ktm25089's post and will present right here:








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Wes K
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Naugha
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PostPosted: Sat Aug 14, 2021 2:28 pm    Post subject: Reply with quote

I had seen that DIY post, but my untutored mind concluded this was not exactly the mod I envisioned. Correct me as needed, gently if possible. 🙂

The ktm25089 post shows (I think) a civy wire with a civy plug (maybe a 295) in one end ... and the other end modified so as to fit his original military distributor. That’s why he cut off four military plug wire ends and attached them to his civy wires.

I am thinking about a military plug wire ... that is joined to a M38 compatible civy plug..... without damaging the wire or the plug..... which I think is what the various commercial ‘plug adapters’ do.... plus they add a surrounding tube which makes the assembly waterproof and lends a ‘military look’

A DIY adapter assembly would cost less and offers the possibility of using the upper metal tube section of a dead/discarded military spark plug as a cap/shroud .. looking much more like the plugs we can no longer find.

I do not know yet if there is a civy plug (M38 compatible) with a top section that would fit inside the top tube section of a military plug.

Again, just piddling around..... yes, tedious ... sorry. Don
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Don Alvarez
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RonD2
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PostPosted: Sat Aug 14, 2021 3:39 pm    Post subject: Reply with quote

I was predicting you'd say that. Surprised

Ok Don, gently.....
You're suggesting a cheap alternative adapter that can also use military waterproof plug wires with civilian spark plugs because paying $30 each for an existing proven solid adapter design is too much to pay one time to use commonly available $3.25 each civilian plugs instead of impossible-to-find and crazy expensive military 2243 spark plugs?

And you think this cheaper adapter for a HIGH VOLTAGE spark plug can be fabricated fairly easily by the average DIY'er cutting a piece from a salvaged military plug and somehow grafting or adapting that piece onto a civilian plug, so as to also be a reliable, but cheap adapter?

Does that about describe what you're suggesting?

Keep us posted when you get to the testing phase!

Good luck!
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Ron D.
1951 M38 Unknown Serial Number
1951 M100 Dunbar Kapple 01169903 dod 5-51

“The only good sports car that America ever made was the Jeep."
--- Enzo Ferrari

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Naugha
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PostPosted: Sun Aug 15, 2021 7:02 pm    Post subject: Reply with quote

The shroud can be constructed in three different lengths depending on how much you cut off the base of the military plug. One of those mods produces a plug that looks almost like the real deal. The challenge will be the military plug wire attachment to the 295.

Is there someone out there who has already worked out a stable way to replace the wire tip of a military cable with the typical attachment sleeve and rubber shroud found on most civy spark plug ends?

The internal alteration of the military cable to a civy plug attachment would be hidden by the cap that screwes onto the plug-mod.







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Don Alvarez
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Naugha
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PostPosted: Tue Aug 17, 2021 5:55 am    Post subject: Reply with quote

Quote:
You're suggesting a cheap alternative adapter that can also use military waterproof plug wires with civilian spark plugs because paying $30 each for an existing proven solid adapter design is too much to pay ...”

I clearly need more info about the various adapters available but have not found much/anything in the way of reviews. Ron, did you say you use them?

* About $120-$190 per set depending on the adapter.
* Different models including one plastic version which is (I think) $15/per.
* Some reports of length issues.
* Reviews ???

Do you have the low down on these parts?



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Don Alvarez
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RonD2
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PostPosted: Tue Aug 17, 2021 2:31 pm    Post subject: Reply with quote

Don,
See my first post back on page 1 of this topic.
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Ron D.
1951 M38 Unknown Serial Number
1951 M100 Dunbar Kapple 01169903 dod 5-51

“The only good sports car that America ever made was the Jeep."
--- Enzo Ferrari

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RonD2
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PostPosted: Tue Aug 17, 2021 10:11 pm    Post subject: Reply with quote

Hey Don,
In case it's helpful as you fabricate your solution, this outfit has a great selection of ignition terminal products https://brillman.com/shop/?fwp_product_category=products-g-ignition-terminals-and-boots
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Ron D.
1951 M38 Unknown Serial Number
1951 M100 Dunbar Kapple 01169903 dod 5-51

“The only good sports car that America ever made was the Jeep."
--- Enzo Ferrari

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