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Sparkplug extension at plug wire end

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  • Sparkplug extension at plug wire end

    Has anyone ever seen or know of a sparkplug extension that looks like the one in this picture? The plug is a Rimfire .25-32. I want to nest this plug down between two rocker arms and not have the spark shorting out and snapping to the rocker arms instead of to the end of the sparkplug. The red and yellow parts I show is the extension. The purple is the original rimfire sparkplug. The red part would have to be steel or brass. The yellow part would be something non-conductive that was resilient like rubber so it would "grip" the end of the sparkplug. Strange question, I know, but I have a reason to ask.---Brian
    Brian Rupnow
    Design engineer
    Barrie, Ontario, Canada

  • #2
    What is the green part and it's I.D.?

    Edited to add: Could you not use a deep well spark plug boot commonly used on automotive OHC engines?
    You may have to reduce the plug insert diameter. Not sure of the size of the Rimfire plug.
    Last edited by Willy; 09-12-2021, 07:08 PM.
    Home, down in the valley behind the Red Angus
    Bad Decisions Make Good Stories​

    Location: British Columbia

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    • #3
      How about turning a piece in the lathe the length of both the red and the gold. Remove the screw on cap from the sparkplug, tap the newly made piece with the same thread in the end so it screws onto the plug. Then just a piece of appropriate size rubber or plastic tubing to slide over it all.

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      • #4
        1982 or so Toyota Corolla spark plug wire were made with a straight extension like that. You can find something similar to:https://www.walmart.com/ip/OE-Replac...X-LE/996623328

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        • #5
          Originally posted by reggie_obe View Post
          1982 or so Toyota Corolla spark plug wire were made with a straight extension like that. You can find something similar to:https://www.walmart.com/ip/OE-Replac...X-LE/996623328
          Some vehicles had hard plastic extensions very similar to the ones in the link you posted. Only possible problem is they all might be too large in diameter for Brian's tiny engine heads and plugs.

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          • #6
            many long years ago, thay made a resistor that snapped on the end of the spark plug to suppress radio static. the conductor was not metal it was carbon. It was about the size of your drawing.but you would need to slip a rubber hose over it for to insulate it. Radio repair shops carried them back then. 1950s-60s. may have to locate some one who restores them.

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            • #7
              I don't have a 1/4-32 plug in my hand to measure it, but if the longest diameter of the plug is not tapered I could make the outer shield from Corian and the inner part from brass or steel. I could quite possibly epoxy the "extension" onto the sparkplug, as it's only about an inch long.
              Brian Rupnow
              Design engineer
              Barrie, Ontario, Canada

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              • #8
                One other idea. Guys used to make up their own spark plug wires for hot rods etc, Packard 440 wire was one of the common wires they used, they sold the wire AND the male/female ends to go on it along with boots. You could take a male and a female end, solder them to a piece of brass rod making a extension, then just slide a piece of hose/tubing over it. Might check the local auto supply houses to see if they sell the wire ends.

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                • #9
                  Originally posted by brian Rupnow View Post
                  I don't have a 1/4-32 plug in my hand to measure it, but if the longest diameter of the plug is not tapered I could make the outer shield from Corian and the inner part from brass or steel. I could quite possibly epoxy the "extension" onto the sparkplug, as it's only about an inch long.
                  Just don't use your favorite JB Weld, it has metal filings in it ! (easily verified with a magnet)

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                  • #10
                    Be careful with your choice of hose.Many years ago in an Auto Shop class the teacher used a length of windsheild washer hose for a plug wire. The thought being that the car would run rough and the kids had to find the problem. The hose sure looked the same as a plug wire. The engine idled very smooth so the teacher reached for the"hose/wire" and got the shock of his life. It seems some hoses have carbon in them to resist sun shine ect. Now this was 45 years ago so newre hoses might be different.

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                    • #11
                      Back a year or two ago, when I was trying to set up a governor on that twin, I designed and built a set of heads that moved the sparkplugs up to the center of the heads. The heads were great, but the sparkplugs were so short that sparks were jumping over to the rocker arm towers.


                      Brian Rupnow
                      Design engineer
                      Barrie, Ontario, Canada

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                      • #12
                        Originally posted by Stepside View Post
                        Be careful with your choice of hose.Many years ago in an Auto Shop class the teacher used a length of windsheild washer hose for a plug wire. The thought being that the car would run rough and the kids had to find the problem. The hose sure looked the same as a plug wire. The engine idled very smooth so the teacher reached for the"hose/wire" and got the shock of his life. It seems some hoses have carbon in them to resist sun shine ect. Now this was 45 years ago so newre hoses might be different.
                        Excellent point and its probably still that way. We have a big warehouse here that stores things for the local Michelin Tire factories, the natural rubber is a brown color as received and they have drums of black carbon they use to give the tires the black color. I am now guessing its the common way of making rubber products black. Never thought about a shock hazard with rubber tube before BUT your story will remain in my memory now.

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                        • #13
                          Originally posted by brian Rupnow View Post
                          I don't have a 1/4-32 plug in my hand to measure it, but if the longest diameter of the plug is not tapered I could make the outer shield from Corian and the inner part from brass or steel. I could quite possibly epoxy the "extension" onto the sparkplug, as it's only about an inch long.
                          This sounds like a very plausible solution Brian.

                          Until I looked up the Rimfire plug I had forgotten how incredibly small these plugs are and I had not associated your .25-32 mention of them as the actual thread size. I missed the decimal in front of the 25 and merely assumed it was a plug number and not the physical description of it's thread size of 1/4"x 32 tpi. BIG DIFFERENCE
                          Duh!

                          You might also be able to affix your solution using a several layers of good quality heat shrink tubing, not the cheap Princess Auto stuff, no comparison in quality.
                          My reason for selecting this method instead of using epoxy is that it is reversible if needed at some later date.
                          I see from the link I left above that boots are also available for these plugs but a quick look-see brings up only 90° boots and not straight ones. However I my search was somewhat time limited so perhaps they may yet exist.

                          Home, down in the valley behind the Red Angus
                          Bad Decisions Make Good Stories​

                          Location: British Columbia

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                          • #14
                            For that size I expect you will be making your own.

                            You might be able to make a split end that would snap over the plug terminal for added security. The insulating hose might want to be a clear silicone, both for insulating qualities, and for heat resistance, as the plug body may get fairly hot.
                            2730

                            Keep eye on ball.
                            Hashim Khan

                            Everything not impossible is compulsory

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                            • #15
                              Originally posted by Stepside View Post
                              Be careful with your choice of hose.Many years ago in an Auto Shop class the teacher used a length of windsheild washer hose for a plug wire. The thought being that the car would run rough and the kids had to find the problem. The hose sure looked the same as a plug wire. The engine idled very smooth so the teacher reached for the"hose/wire" and got the shock of his life. It seems some hoses have carbon in them to resist sun shine ect. Now this was 45 years ago so newre hoses might be different.
                              Some fuel hose standards even have requirement for conductivity to lessen any static electricity.


                              I’d turn the extension from PTFE with a thin wire running trough.
                              Location: Helsinki, Finland, Europe

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