are retracted-gap plugs still being made?

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seattle smitty
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are retracted-gap plugs still being made?

Postby seattle smitty » Sat Sep 09, 2017 1:15 pm

Fifty five years ago or so I was racing outboard hydros with methanol-fueled 2-stroke engines. The plugs we commonly used were Autolite AE 403 or Champion L84R (if using nitro, the plugs would have been the colder AE203 or L82R). These plugs had retracted-gap or "side-wire" ground electrodes. A disadvantage was that these gave the fuel/air charge somewhat worse access to the spark, and a good strong ignition was very helpful, but the advantage was that the side electrode was unlikely to be burned off, as could happen with ordinary J-gap (a Champion suffix) electrodes. (BTW, these retracted-gap plugs are not to be confused with the "surface-gap" plugs which came out in those days, for a different purpose).

Since no spark plug manufacturer would have bothered making special plug types for the tiny world of alky outboard racing, my assumption was that these plugs must have had wider usage, such as in fuel dragsters(???) and maybe something like the speedway motorcycles(??).

I've been trying to Google any current info on the restricted-gap plugs, but without finding much more than odd opinions and misinformation. Do any of you know about this subject, and whether any manufacturer still makes such plugs? So far as I can tell, neither Autolite nor Champion do so.

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Re: are retracted-gap plugs still being made?

Postby pamotorman » Sat Sep 09, 2017 3:22 pm

are these the ones with the pressed in side electrode that needed a special tool to set the gap by pressing in the side electrode ??

kosky racing
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Re: are retracted-gap plugs still being made?

Postby kosky racing » Sat Sep 09, 2017 5:25 pm

Not made anymore common numbers for champs was N57r- N59r- n62r----an on Most use NGK 6061-9-10--11 surface gap plugs are still available

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Re: are retracted-gap plugs still being made?

Postby emsvitil » Sat Sep 09, 2017 5:56 pm

Look up the plugs used for Mazda rotary engines.
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Re: are retracted-gap plugs still being made?

Postby Old as Dirt » Sat Sep 09, 2017 7:19 pm

Smitty,
If you can't find any.. I'm pretty sure I have about a dozen new ones in the boxes.. left over from our Open class Methanol Dirt Kart days..
In Monroe.. so sort of close to you if your name is an indication.. PM me.. :mrgreen:

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Re: are retracted-gap plugs still being made?

Postby RCJ » Sat Sep 09, 2017 9:49 pm

Might look at the autolite X plugs.Search AR3932X

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Re: are retracted-gap plugs still being made?

Postby midnightbluS10 » Sun Sep 10, 2017 1:02 am

Something like a Champion G55R? The "R" in the part number indicates retracted gap.

http://www.sparkplugs.co.uk/champion-ra ... -plug-g55r

Image

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And how to decipher Champion Part #'s. Depending on the shell, they may have what you need. They still sell the C-style shell with retracted gap. See: https://www.amazon.com/Champion-695-C55 ... B0013TOR06

Just change the first letter to match what you need and plug in the part number to Google. Or figure which heat range you'd need, also. Goes from 51 to 69 for racing plugs.

The SP Handbook is on the web at the Cooper site but the Heat Range Chart is not. Both are great little 3 by 8 inch booklets with full color photographs.

If the first letter is "R" it stands for resister. A plug without a resistor would just be called a C12YC. There is some evidence that resistor plugs give slightly better gas mileage, according to both the Champion and NGK websites. The resistor delays the spark initiation but makes it hotter once it does fire.

The "C" is the 'shell' type and sets the threads and hex size. A "C" shell has a 14 mm thread, a 0.750 inch reach (reach is the length of thread), and a 5/8 inch hex bolt size for your sparkplug wrench. The "N" shell is similar to the "C" shell but has a 13/16 hex. Other shells are G, A, J, V, L, and S. The other shells won't fit the Magnum engines - except - the S shell has a .708 inch reach but is otherwise like the C shell. Put one of these 'S' in your Magnum and it would reduce the compression ratio a tiny bit. This might be useful for supercharged engines.

The "12" is the heat range. 12 is about as 'hot' as they go. Champion says that the ditty to remember is:
"Put a hot plug in a cold engine and a cold plug in hot engine."

I think the reason Dodge chose a 12 heat range plug is to pass emissions tests - which simulate stop and go city driving. This is cold engine type driving and the hot plug is there to keep the plug from fouling. The booklets mention that Champion makes colder plugs down at least to a RC9YC .

n Champion's racing sparkplugs they go to a two number heat range system that goes from 69 (hot) to 51 (cold). All racing plugs are very cold and not recommended for street use. In the booklet they have a chart that shows that a RC9YC is about the same heat range as a racing C67YC. This chart also shows that a 'N' shell RN5C is about the same heat range as a 'C' shell RC9YC. Yes, it can be confusing.

The "YC" means "Projected Nose." Quoting from Champion......

"This gap style projects the spark an additional .060 inch into the combustion chamber for a total projection of 0.210 inch, and providing there is sufficient clearance to valves and pistons, provides the ultimate in performance. Initiating the flame front closer to the center of the combustion chamber has a similar effect to advancing the timing. Therefore, maximum timing may be reduced which helps reduce the chance of detonation and provides superior part throttle response. A second valuable feature of this style is a broader heat range. The core nose is longer, providing a 'hotter' plug at low speed which helps prevent fouling. As engine speed increases, the incoming air/fuel mixture flows across the tip of the core nose, providing charge cooling which effectively reduces heat range at higher engine speeds for increased preignition and detonation protection."

Other gap styles from Champion are:

Regular gap (no letter)
'V' Surface gap (like the Bosch Super 4 - turns spark 90 degrees)
'R' retracted gap (for supercharged and ultra high compression)
'JC4' cut back ground electrode (for Winston Cup & Trans Am)
'A' angled gap
Fine Wire Electrode gap 'FWE' (fine wires fire at lower voltages and fire better in very rich or very lean mixtures according to Champion. )
Last edited by midnightbluS10 on Sun Sep 10, 2017 1:37 am, edited 3 times in total.

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Re: are retracted-gap plugs still being made?

Postby midnightbluS10 » Sun Sep 10, 2017 1:23 am

Also found this at yellowbullet. Would something like this work at all? It's a Bosch plug. Not sure if Alex ever figured out which plug that was exactly or whether he got more or replaced them with something similar.

http://www.yellowbullet.com/forum/showt ... p?t=502094

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Re: are retracted-gap plugs still being made?

Postby englertracing » Sun Sep 10, 2017 1:42 am

The champion g55r and g57r are standard equipment in methanol fueled 500cc 4 stroke speedway bikes

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Re: are retracted-gap plugs still being made?

Postby seattle smitty » Mon Sep 11, 2017 11:43 am

[quote="pamotorman"]are these the ones with the pressed in side electrode that needed a special tool to set the gap by pressing in the side electrode ??[/quote] Yup, those were the ones.

The Champion G55R/57R referred to by Englertracing look to be the same gap style, though with a much longer reach shell (the old L- series was 1/2" reach). With the changes in numbering systems over the years (WHY?) it's hard to be sure that today's cross reference charts are really comparing apples to apples, but I'm guessing those Champions are not as cold a heat range as the L87/84/82R that I knew, years ago (maybe comparable to the old L57/54/52s). OTOH, that extra-long reach does give more of a heat-sink. One of the great things about racing 2-strokes is that a reasonably good home-shop tuner can do a lot of his own development work, which in this case could include carving out his own custom racing head on a Bridgeport as I once did (250cc Konig), the point being that a shorter or longer plug reach need not be a deal-killer in this situation.

That NGK plug, with the welded side-wire, is interesting in that it looks like it would take a lot more heat without melting than more usual ground wires, midnightbluS10. Had not seen that one (but then there's a lot I don't know!).

Incidently, I phoned the Champion tech line, and I asked for and got "an old guy" who had been there a while. However, he evidently was not clued in to the racing side of things, didn't know about my old plugs, and couldn't find anything helpful on his charts. Which is why I came here. You need a real ancient codger to talk about anything that was current when I was young and handsome (and stupid) :lol:

Thanks to all for the help.

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Re: are retracted-gap plugs still being made?

Postby englertracing » Mon Sep 11, 2017 12:23 pm

what are the dimensions on the plugs you are looking for?

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Re: are retracted-gap plugs still being made?

Postby pamotorman » Mon Sep 11, 2017 12:55 pm

seattle smitty wrote:
pamotorman wrote:are these the ones with the pressed in side electrode that needed a special tool to set the gap by pressing in the side electrode ??
Yup, those were the ones.

The Champion G55R/57R referred to by Englertracing look to be the same gap style, though with a much longer reach shell (the old L- series was 1/2" reach). With the changes in numbering systems over the years (WHY?) it's hard to be sure that today's cross reference charts are really comparing apples to apples, but I'm guessing those Champions are not as cold a heat range as the L87/84/82R that I knew, years ago (maybe comparable to the old L57/54/52s). OTOH, that extra-long reach does give more of a heat-sink. One of the great things about racing 2-strokes is that a reasonably good home-shop tuner can do a lot of his own development work, which in this case could include carving out his own custom racing head on a Bridgeport as I once did (250cc Konig), the point being that a shorter or longer plug reach need not be a deal-killer in this situation.

That NGK plug, with the welded side-wire, is interesting in that it looks like it would take a lot more heat without melting than more usual ground wires, midnightbluS10. Had not seen that one (but then there's a lot I don't know!).

Incidently, I phoned the Champion tech line, and I asked for and got "an old guy" who had been there a while. However, he evidently was not clued in to the racing side of things, didn't know about my old plugs, and couldn't find anything helpful on his charts. Which is why I came here. You need a real ancient codger to talk about anything that was current when I was young and handsome (and stupid) :lol:

Thanks to all for the help.

if you can get tungsten rod in the right diameter you could make your own recessed side electrode plugs. just remove the welded on one and drill into the shell for a press fit

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Re: are retracted-gap plugs still being made?

Postby MadBill » Mon Sep 11, 2017 7:23 pm

"if you can get tungsten rod in the right diameter.."

Or iridium. Bet McMaster-Carr has both in stock, in any desired diameter.. :D
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Re: are retracted-gap plugs still being made?

Postby midnightbluS10 » Tue Sep 12, 2017 2:42 am

seattle smitty wrote:
pamotorman wrote:are these the ones with the pressed in side electrode that needed a special tool to set the gap by pressing in the side electrode ??
Yup, those were the ones.

The Champion G55R/57R referred to by Englertracing look to be the same gap style, though with a much longer reach shell (the old L- series was 1/2" reach). With the changes in numbering systems over the years (WHY?) it's hard to be sure that today's cross reference charts are really comparing apples to apples, but I'm guessing those Champions are not as cold a heat range as the L87/84/82R that I knew, years ago (maybe comparable to the old L57/54/52s). OTOH, that extra-long reach does give more of a heat-sink. One of the great things about racing 2-strokes is that a reasonably good home-shop tuner can do a lot of his own development work, which in this case could include carving out his own custom racing head on a Bridgeport as I once did (250cc Konig), the point being that a shorter or longer plug reach need not be a deal-killer in this situation.

That NGK plug, with the welded side-wire, is interesting in that it looks like it would take a lot more heat without melting than more usual ground wires, midnightbluS10. Had not seen that one (but then there's a lot I don't know!).

Incidently, I phoned the Champion tech line, and I asked for and got "an old guy" who had been there a while. However, he evidently was not clued in to the racing side of things, didn't know about my old plugs, and couldn't find anything helpful on his charts. Which is why I came here. You need a real ancient codger to talk about anything that was current when I was young and handsome (and stupid) :lol:

Thanks to all for the help.


I covered how to get the plug you need in my post. Reach is determined by the shell. Different letters differentiate the different shells. Check em. See if one matches what you need. If so, plug the letter into the part number. It's all explained in my post. They carry an "L" shell for those plugs. See if it has the reach you need. If so, the part number will be L**R where "**" is the heat range determined in range 51 to 75.

According to their chart, the L series shell has a 1/2" or .472 reach. I'd start there.

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Re: are retracted-gap plugs still being made?

Postby kosky racing » Tue Sep 12, 2017 6:15 am

I have several boxes of n-57 if interested


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