12v reproduction coil

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Tigerman67
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12v reproduction coil

#1

Post by Tigerman67 »

I believe I had a 12v reproduction coil go out on me, but I want to check if what happened was normal, and is there anything I should have done on my end.

I bought the chrome reproduction 'square' 12 v coil, I got it from J&P, I thought it was a Vtwin part, but i checked J&P, and they don't mention manufacturer.

Been running for less than 500 miles, when it was missing badly. Thought i had fouled a plug badly. Swapped in a new set of plugs even though the old ones didn't look bad. Still ran kind of rough when I took it out at lunch time, but on the way home back it was running fine again. Come out to ride it home, and it was a bugger to start and then only ran on the back cylinder.

I was guessing bad plug wire or bad coil. I had a more modern coil that was originally on the bike when I bought it, and I hooked that up, and the bike starts and runs fine. Looking at the repro coil the 'pin' on the side of the coil feeding the front cylinder appeared to be off center, and a bit blackened and maybe even melted, hard to tell actually, its tough to see in those holes.

My theory is that it didn't make good contact with the plug wire center, and torched itself because it had to arc to make contact with that wire which caused the miss.

A few other details. The coil wasn't marked + or - on the terminals. I got caught in a massive rain storm the other day, but was sheltered in Home Depot for most of it, and the bike ran fine after that, but sat for a few days after that before I had this problem.

So I guess my question is, should I have returned the coil if I had noticed that the pin was off center? Should i have used dielectric grease on the plug wire fittings? Anything I should have done on my end to prevent this?
58flh
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Re: 12v reproduction coil

#2

Post by 58flh »

Tigerman---Thats how they start to go!--I have seen NEW ones from a blisterpak DEAD before even used!--You didnt do nothing wrong for that junk coil!--(I use di-electric grease on wires to)-But thats not what killed it!---Its JP that killed it!--If you want a good 12-V coil Use a good used OEM one or SPEND the mony & get youself a QUALITY COIL like DYNA or C-Fire,etc.---Respectfully---Richie
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Re: 12v reproduction coil

#3

Post by old.wrench »

Tigerman,
It takes a little bit of switching around, but the best way I've found of identifying a suspected bad coil is simply to swap it out with a coil that you know is good. I know there is a way to check a coil with test equipment, but I think most of us that have run into coil problems just "test" with a known-to-be-good coil. You are not the first one to encounter problems with the re-popped old-style coils. It's a bit of a crap-shoot with those coils; If you get a good one it will work just fine, but if you get a bad one . . . :) . I've got one of the re-pops (12 volt) that has been working flawlessly for 3 years.

Geo.
1951 adam
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Re: 12v reproduction coil

#4

Post by 1951 adam »

I ran into the same issue when I had the 12v square coil, lost my frt. cyl. But was able to limp home. Yesterday I rode for 2 hours, bike got hot , and started missing .now this is a 6v repro coil . First I thought fuel issue, pulled up reserve , stopped for gas. It would start to break up accelerating in 3rd and fourth, ok I thought a fouled plug....nope. Got home put in another condenser ... Same.
Today I checked the wire end in the coil, that feeds the frt plug , and it was green! I had just put those wires on a few months ago with electrical grease and bike had not seen water.... Weird. Rear feed was clean... Weird. Cleaned it up, popped in plugs. Cold it's fine , hot I got a slight miss sometimes. I think when the coil heats up it starts to lose it. I'm done with these aftermarket coils , I'd rather buy 5 swap meet coils , to find one good one , then to run that crap.
Adam
Tigerman67
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Re: 12v reproduction coil

#5

Post by Tigerman67 »

Thanks guys. I had read a few of the other posts, in particular the one about some of the repro coils being wound back was very interesting. I hadn't checked the coil to see if I was backwards, as I think I just looked up the correct wiring for a stock one. So I might have had that problem, but I think my offcenter pin would have bit me reguardless.

It was nice that I happened to have that spare coil laying around to be able to swap out and test. I wasn't planning on running that coil since the plastic mount broke on it, and that is why i stopped running it. I epoxied it back together when I was epoxying something else a few weeks ago, but I doubt it will last with the vibration on my 51. But I might run it for a few days while I wait for a replacement.

I am sending the repro coil back, its recent enough that it should fall under the return policy. If an exchanged coil doesn't have centered posts, I will send back immedaitely. If it looks good, I will chance it, but I may have to throw my spare in the tool bag even though its a bit big to be lugging around in a small tool bag.

Since I am running 12v, I assume that no stock bikes came with that square style coil in 12V? So I have never looked for a used stock coil.

I am going to order a dyna coil as insurance, since I don't think my currnet backup's mount will last long. If the new repro doesn't last long, then I will switch to the Dyna.

I choose to not ride mine home when the front cylinder was completely dead, wasn't sure if there was a chance that I would wash out the rings with it not firing at all. i was thinking about just doing the coil swap in the parking lot where it was, but it was getting dark, so the bike got a ride on the trailer instead.

thanks everyone
1951 adam
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Re: 12v reproduction coil

#6

Post by 1951 adam »

No square coil was ever 12v originally .
Adam
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Re: 12v reproduction coil

#7

Post by Bigincher »

Sometimes you just have to take the penalty and put the bike on the trailer. You lose all your points for that trip, but it's better than doing damage to your bike somehow. (Old inside joke on the "points for the trip"...... :wink: )
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Re: 12v reproduction coil

#8

Post by panhead_kicker »

31609-65A is still available from Harley, and reasonably priced compared to aftermarket, not sure who makes it. Andover coils made in Indiana , one of the original suppliers to Harley is still around too, but I don't know that I've used their product. I've run one from Harley for 3 years and no problems.
1951 adam
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Re: 12v reproduction coil

#9

Post by 1951 adam »

"I choose to not ride mine home when the front cylinder was completely dead, wasn't sure if there was a chance that I would wash out the rings with it not firing at all. i was thinking about just doing the coil swap in the parking lot where it was, but it was getting dark, so the bike got a ride on the trailer instead."

These old bikes are pretty tough, that's why we can reuse and restore these old parts, I guess you got to use your better judgement,
Adam
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Re: 12v reproduction coil

#10

Post by awander »

On tractors and cars, many "12V" coils are simply a 6V coil with an internal resistor to allow use on a 12V system. On some of the tractors and cars, the resistor is external to the coil.

Not sure why that wouldn't work to put an original 6V square coil on a 12V bike.
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Re: 12v reproduction coil

#11

Post by VPH-D »

I like to use the -65A coil, with the -78 coil mount on 12 volt conversions. Looks OK, and the coils last a long time.
VPH-D
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Re: 12v reproduction coil

#12

Post by panfreak »

When my piece of crap repop coil died just like yours many years ago, I gently pried top off and drilled holes down into it which emerged at the lower/back, exiting right by the seat tube. I put an accel coil in my tool box, and ran long spark wires from there, up through the square coil (with top cap back on of course) and used the same finger nuts etc. and even fake wires from the terminals. I was concerned about the longer spark plug wires, but I put thousands of miles on it without a problem. Ran wayyyy better with that coil as a matter of fact. I went through a couple show and shines and no one ever did see what I'd done, I was careful to hide everything so you couldn't see unless you really tried. Only draw back was space in my tool box but knock on wood I haven't needed much in that way yet. It was an experiment because I had loads of spark wire, a dead square coil and a spare accel off another bike in a box of junk; I'm not saying everyone should do it, I just wanted the stock square look as my bike was not a chopper back then. If it failed there was no loss, I would've sourced out a better quality coil.
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