Spark plug sub
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Tourer
Joined: Nov 2021
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From: FL winter, northern MI summer
Spark plug sub
I've used the Champion 12JYC plug in my shovel. Is it possible to use the resistor plug (R12JYC)?
Reason I want to do it is they have a much longer threaded body, probably because the resistor cools it, and it needs to get closer to the piston for the same heat.
Reason I want to do it is they have a much longer threaded body, probably because the resistor cools it, and it needs to get closer to the piston for the same heat.
Tourer
Joined: Sep 2020
Posts: 487
Likes: 289
From: Northern MN
Without looking up my plug number,
I had the short stubby plugs in my bike when I bought it and the threads in the head were pretty shot. I had to but the long thread plugs so there were more threads holding in the plug. Bike runs great. 79 FX
Tom
I had the short stubby plugs in my bike when I bought it and the threads in the head were pretty shot. I had to but the long thread plugs so there were more threads holding in the plug. Bike runs great. 79 FX
Tom
Road Master
Joined: Jun 2013
Posts: 1,239
Likes: 1,171
From: St. Catharines, Ontario
I'm confused a little. You're putting long reach plugs in a short reach head? I would strongly recommend not to , it may get closer to the piston than you want.
Lowoilpressure, your '79 if original heads would have been long reach anyway, PO probably installed wrong plugs.
Lowoilpressure, your '79 if original heads would have been long reach anyway, PO probably installed wrong plugs.
Last edited by Baird; Jul 8, 2022 at 06:05 AM. Reason: more info
Road Captain
Joined: Jul 2021
Posts: 605
Likes: 441
From: BRIGHTON, ENGLAND
someone beat me to it, but your year should have long reach plugs anyway, & forget the resistor bit, better spark un-resisted.........I have been using HARLEY plugs in my Shovelhead, not as expensive as Champion, plus over the years I have gone off Champions in favour of NGK, never had luck getting them to last ...
Road Master
Joined: Jun 2013
Posts: 1,239
Likes: 1,171
From: St. Catharines, Ontario
someone beat me to it, but your year should have long reach plugs anyway, & forget the resistor bit, better spark un-resisted.........I have been using HARLEY plugs in my Shovelhead, not as expensive as Champion, plus over the years I have gone off Champions in favour of NGK, never had luck getting them to last ...
Last edited by Baird; Jul 8, 2022 at 01:07 PM.
Road Captain
Joined: Jul 2021
Posts: 605
Likes: 441
From: BRIGHTON, ENGLAND
Baird, the only thing I had that loved Champions was an old WLC45 I had in the late 70's, when i bought it i(n boxes & in pieces) it came with a 10 box of lovely old big Champions, never had to buy a plug in the 15 years i had it, I tried them in various other Harleys & yea, they worked well, just didn't last, the shovel I have now has HD plugs, not sure who makes them for Harley, they might even be Champions at heart..??
Last edited by magnum45pete; Jul 8, 2022 at 01:49 PM.
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Tourer
Joined: Nov 2021
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From: FL winter, northern MI summer
Thanks for the replys.
I wrote a long reply last night, and it dissappered, I must have hit the wrong button. I'll try and keep this shorter on why I want a longer plug.
The front plug was only holding by a couple threads, so last year I put a Helicoil in, not that brand, but a "Plug Saver" insert. I have around 1,000 miles on it, and a couple weeks ago coming in from a ride I was thinking how this bike never ran better, it was like music going down the road. I get about a mile from the house, and it starts poppiing, I guessed it was a condenser because this shovel eats them.
I change the condenser, and it still is popping, the front cylinder is noticeably hotter just idleing in the garage, I'm now thinking its the O-riings in the intake. I check that out and its fine. I do a compression check, and the back is 90, front is 35. I pull the front head, and I can see light around part of the helicoil. The thread of the aluminum must have separated.
I take it to an auto machinest, he takes the helicoil out with an easy out, but it destroys the threads. He can't help any more, and sends me to a machine shop.
The machine shop says they have to weld the hole shut, re bore and thread. The weld would be softer than the parent aluminum head, but should last just fine. Thats where its at now, I don't know when I will get it back. I just thought since the plug is so short threaded, and looks like there is plenty of room, a few more threads will help. I just am concerned with the heat range. I thought maybe the resistor plug of the same designation would be the same heat, and it has lots more threads.
If that doesn't work out, I'll probably spring for the S&S head.
The rear head has a helicoil that was installed by a hot rod speed shop. Its been in there over 25 years, and been great.
I wrote a long reply last night, and it dissappered, I must have hit the wrong button. I'll try and keep this shorter on why I want a longer plug.
The front plug was only holding by a couple threads, so last year I put a Helicoil in, not that brand, but a "Plug Saver" insert. I have around 1,000 miles on it, and a couple weeks ago coming in from a ride I was thinking how this bike never ran better, it was like music going down the road. I get about a mile from the house, and it starts poppiing, I guessed it was a condenser because this shovel eats them.
I change the condenser, and it still is popping, the front cylinder is noticeably hotter just idleing in the garage, I'm now thinking its the O-riings in the intake. I check that out and its fine. I do a compression check, and the back is 90, front is 35. I pull the front head, and I can see light around part of the helicoil. The thread of the aluminum must have separated.
I take it to an auto machinest, he takes the helicoil out with an easy out, but it destroys the threads. He can't help any more, and sends me to a machine shop.
The machine shop says they have to weld the hole shut, re bore and thread. The weld would be softer than the parent aluminum head, but should last just fine. Thats where its at now, I don't know when I will get it back. I just thought since the plug is so short threaded, and looks like there is plenty of room, a few more threads will help. I just am concerned with the heat range. I thought maybe the resistor plug of the same designation would be the same heat, and it has lots more threads.
If that doesn't work out, I'll probably spring for the S&S head.
The rear head has a helicoil that was installed by a hot rod speed shop. Its been in there over 25 years, and been great.
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Tourer
Joined: Nov 2021
Posts: 479
Likes: 319
From: FL winter, northern MI summer
I have been using the Autolite 4275. I haven't had any issues with any brand, NKG, Champion, Autolite, Accel etc.. It seems like there was a two numbered Autolite that some used, (85?). I don't know what would be the difference. I tried them all, never could see a difference, so went with the $3 Autolite.
When I ran 2 stroke dirt bikes, there was a definate difference, NGK were my favorite, Champs were the worse.
When I ran 2 stroke dirt bikes, there was a definate difference, NGK were my favorite, Champs were the worse.
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