M38 converted to 12V. I have a couple of reasons to mistrust the ignition coil and will replace it. It's marked "12V - External Resistor Required" (make and part number unknown, secondary measures low 8k ohms, and suspect off-shore junk). I have a good 1.5 ohm ballast resistor in the primary circuit and understand I need a ballast-required 12V coil that also has a 1.5 ohm primary to make the necessary 3 ohms to induce the proper secondary voltage output. I also have the circuit to put 12v on the coil primary only when cranking.
Is there a correct range for coil secondary output voltage for the L134 motor? Not that I could measure it, but more to try and find specs from a manufacturer to buy the right coil out the gate. Vendors seem to publish the primary ohms rating to match a ballast resistor, but not much else. Research and the SM offer no joy.
Back in the day I'm sure I could go to any auto parts store and get a coil for a CJ-3A and call it a day. Not so now. Only one vendor I've found (Brillman) publishes that spec for the two likely ballasted 12V coils they carry (one is 28,000 volts and the other 55,000 volts --- quite a spread). Asking in a modern auto-parts store gets nowhere fast. Seems like only the race car folks care about coil output these days --- and I'm thinking 80,000 might be too many?
In other words, should I care about coil secondary voltage on a L134 motor? Run like crapola or damage the motor if not in the ballpark? Over thinking it? Should I just buy the first 12 volt ballasted coil I can find and be happy?
Your advice and/or pointers to a good quality ballast-needed coil part number for a 12V L134 motor would be most appreciated. _________________ 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
Internal resistor coils vs external resistance (Ext Ballast Resistor) coils. Running performance V-8s with a lot of ign timing advance in the 60's caused the low rotation, especially with a warm engine, so a hot shot of coil juice was a handy reserve option thus the popularity of the external ballast resistance coils which normally provided coil power with the proper resistance but would allow a hot shot of no resistance voltage while cranking.
This crap is not necessary on a 60 HP L134 or a 72 HP F134. The 12 volt coil used thru the 60's to the end of the F134 use was the Prestolite 200691. Internal resistor coil. Primary resistance spec is 3.9 to 4.2 Ohms and secondary is 9400 to 11,700 Ohms. The only other test spec is the amp draw which should be 2.6 amps @ 12.5 volts.
Since you are running the jeep 12 Volt you should get a copy of SM 1046 for the 12 volt cj's and a copy of the Autolite/Prestolite Test Specifications dated sometime between 1955 and 1971. The illustrations below are from my 1960 copy:
Joined: Oct 02, 2014 Posts: 1926 Location: South Carolina, Dorchester County
Posted: Sat Jul 21, 2018 4:51 pm Post subject:
Thanks Wes. There's quite a bit of dialog (some yours, going back years) in this forum and other CJ forums saying the ballasted coil set up is a good thing for the L134 with many happy folks. Good not meaning "necessary" obviously.
You suggest I ditch the ballasted coil, which prompts a follow-up question --- it's my (limited) understanding that the ballasted set-up is "easier" on the points, because the 8 or so volts on the primary after the resistor is plenty to generate a secondary output sufficient for the L134 to run properly --- and points supposedly last longer than they do when using the full 12V all the time. And the other circuit that puts 12v to the primary just for cranking is maybe an unnecessary bonus for me as there's not much cold starting in South Carolina. If it's true that the ballast set up has these benefits, then because I'm currently wired that way, I'm kind of inclined to keep it up. Coil prices for either coil type are about the same, and a ballast resistor is less than $10, no big deal.
If it's not true, and it's 6 of one, half-dozen of the other and I should switch to a no-ballast set-up it's easy enough to change over. My truck won't be a daily driver and I can afford $5 to replace points a bit more often than otherwise.
My original post question also still hanging: about how many thousand volts should I be looking for out of a ballasted or no-ballast coil secondary for the L134? For example, is the Brillman 28,000 volts enough? 55,0000 too much? Does it matter? I don't want to be too hard on the old gal. If I can't find a spec or advice for kilo-volts, I guess maybe any coil with a secondary spec of 9 to 12k ohms would do. In other words, WWWD? (What Would Wes Do?)
I have a copy of SM 1002-R6 covering CJ-2A through CJ-6. But it doesn't say anything about coil specs. Is the SM 1046 better? I'll also look for a copy of the Autolite/Prestolite Test Specs. Hard to find? Any clues who has them most appreciated. Pay you to mail me a copy of yours?
Thanks again ! _________________ 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
28Kv is plenty. as compression pressures go up, it takes a higher voltage to break down the air gap of a spark plug. L134 engines are anything but high compression engines, actually probably the lowest CR of anything running around the streets.
55Kv will cause premature failure of the distributor cap and stock wires won't like it either. High voltage systems using those voltages have 8MM or bigger wires to the plugs. And that just doesn't look right on an L134. _________________ '52 Dodge M37, '42 GPW, '48 FrankenJeep CJ2A/M38, '50 CJV-35(U), '51 M38, '42 WC-57 Command Car, '44 WC-51 Weapons , (2) M1941 Sperry 60" Anti-Aircraft Searchlights, John Deere M-gator, '44 White M3A1 Scout Car
I did not suggest you ditch it. I pointed out that aftermarket coils and ballast set-ups were a necessity on high compression modern V-8s but absolutely unnecessary on a L134 or F134. In fact Willys Kaiser did not use those hi-output coils or external ballasted systems/coils.
Those high secondary voltages are seldom used in any coil spec sheets but often seen in advertisements for aftermarket units. Main reason is for the average public they are not measurable.
You can buy a 200691 Prestolite coil or a cross ref and know that it is adequate for your Jeep.
Joined: Oct 02, 2014 Posts: 1926 Location: South Carolina, Dorchester County
Posted: Sat Jul 21, 2018 10:16 pm Post subject:
Thanks Wes. My apology. I took your comment "This crap is not necessary on a 60 HP L134 or a 72 HP F134." as a ditching suggestion. Or that you wouldn't use it yourself.
Your opinion is important to me. I'm still a rookie at this and would rather not experiment with stuff you learned decades ago --- if I can phrase a question adequately.
Thank-you for the part number leads for non-ballasted coils.
And thanks mdainsd ! _________________ 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
Ron, There is one small tool I forgot to mention. With it you can determine kilovolt capability of your coil.
Quote:
Thexton manufacturing Company - gnition Spark Tester [404]
Works on ignition systems from high energy electronic automotive systems to small engines. Tests for no start conditions and for spark strength. Adjustable gap allows for spark gap requirements from 0 to 40,000 volts. Gauge background makes spark easy to see for accurate measurement. Alligator clip securely fastens to ground. Screw assembly adjusts spark gap quickly and easily. Includes safety shield.
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