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Sparkplug extension at plug wire end

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  • #16
    Brian, we used to use Vaseline smeared on to waterproof the magneto and HT leads of motorcycles so we could ford rivers. Maybe something similar coating the plug and lead will stop arcing?

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    • #17
      Quite a few years ago (in the 60s) I had two different Citroens, ID19, that had extensions on the plugs due to the big valve covers on the engines. Course those were full size plugs. :-)
      ...lew...

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      • #18
        I agree with matti. A teflon tube with a thin centre conductor should do it. A foot of teflon rod is only ~10 bucks on ebay.

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        • #19
          Okay---Don`t laugh.--I have a solution. The inner portion will be made from brass. The outer section will be kiln dried oak wood. The brass core will be Loctited into the wooden outer shell. The wooden outer shell will be Loctited to the sparkplug. The sparkplug never gets hot enough to burn the wood. The wood is a good insulator, and the brass passes the current down to the sparkplug. best part of all is that I have the material to do this.
          Brian Rupnow
          Design engineer
          Barrie, Ontario, Canada

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          • #20
            And with a nice wooden base it will add some old world flair to the final presentation.
            It won't take much to deter the errant spark jumping and this will add a unique look. I mean really, when was the last time anyone has seen what appears to be a wooden spark plug?
            Home, down in the valley behind the Red Angus
            Bad Decisions Make Good Stories​

            Location: British Columbia

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            • #21
              You might consider epoxy instead of Loctite. Loctite crosslinks tin the absence of oxygen to form a bond, unfortunately, it also melts at fairly lo temps (~300F) to release the bond. If you are using Loctite super glue, ignore all the above.

              Mike

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              • #22
                Dry wood is a decent insulator, but not perfect, especially at higher voltages. Something like varnish soaked into the wood might be a useful addition.

                I'd consider dry wood a good insulator at 240V, but might have some questions at 20,000 volts.
                2730

                Keep eye on ball.
                Hashim Khan

                Everything not impossible is compulsory

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                • #23
                  I didn't read all the replies in detail yet. But so far no one had mentioned that the trait you are looking for is a material with a high dielectric strength? This trait being the voltage per thickness which the material can withstand before it arcs through.

                  Something rubbery or from plastic would be the easiest way.

                  Looking at a couple of links it looks like good ol' natural rubber is the best. At THIS LINK the last table about 2/3's of the way down the page near the end has a section on common insulators. Natural rubber is listed as being 100-215 Kv/mm for dielectric strength.

                  Another search for dielectric strength of plastics put me onto THIS OTHER PAGE where out of the provided list Teflon is a clear winner at the listed 60-70Kv/mm But at the first page the same stuff (polytetraflouroethylene) only gets a rating of 19.7 Kv/mm. So the tables don't always match up and some more searching of this would be wise. But this is the quality you are looking for in an insulator.

                  Looking around at rubber a little more I'm finding a more believable rating of 30-40 Kv/mm. Keep in mind that this would depend on any colorants like carbon black and other additives. It may well be that the best cover if rubber is your choice would be simply a layer or two of common light brown/tan latex tubing

                  If your original head with the arcing did not use an insulative cap at all then almost anything you use will be better than nothing. But picking one that has the highest rating will mean you can squeeze things a little tighter without any issue. Air is listed as having a dielectric strength of around 3Kv/mm. So just about anything you can use is better than that.

                  Last second check. Found THIS OTHER PAGE listing plastics and it looks like straight PTFE (Teflon) is still the best in terms of the highest breakdown voltage per thickness at 50 to 170 (no idea why the wide range). But even UHMW polypropylene is no slouch at 28 Kv/mm. If you have some plain white UHMW on hand it'll be 8 times better than air. But clearly PTFE/Teflon is better even if it only meets the minimum of 50 Kv/mm.

                  Chilliwack BC, Canada

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                  • #24
                    Oh. and one other thing. You want your extension to cover the entire length of the ceramic top post on the plug just as you show in the drawing. But don't forget to include extra length above the contact point too. The reason being you need to extend the possible travel path through the slight amount of air between the wire and any insulation boot.

                    I've got some of these little 1/4-32 plugs for my old time spark engines. And there's not much room to work with. I think my mode of attack in the same situation might be to slip the PTFE boot over the wire and then actually solder the end of the wire to the end of the plug's tip so the connection is highly axial. Then slip the PTFE boot down over the connection and ceramic. That'll ensure that I can maintain the most distance from any grounds around the boot and keep the maximum thickness of insulator between the HT lead and any ground parts of the valve train.

                    EDITED- Modified the above to reflect the details in your last drawing. But I'd also pass on the idea of wood which is not easy to find a spec for the dielectric strength vs more typical insulators such as natural rubber and all the usual plastics. Plus working with an easy to split wood such as oak at that size range would not be fun.
                    Last edited by BCRider; 09-14-2021, 12:10 PM.
                    Chilliwack BC, Canada

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                    • #25
                      Originally posted by The Artful Bodger View Post
                      Brian, we used to use Vaseline smeared on to waterproof the magneto and HT leads of motorcycles so we could ford rivers. Maybe something similar coating the plug and lead will stop arcing?
                      The modern method is Silicone Dielectric Grease, available at any part source store.

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                      • #26
                        Carbon is sometimes used in plastics for obtaining a black color. I heard a story once where an electronic manufacturer purchased some black, plastic sheets to make terminal boards for audio. They had all kinds of cross talk which took some time to trace to that carbon filled plastic. They had neglected to specify "non-conductive".



                        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.
                        Paul A.
                        SE Texas

                        And if you look REAL close at an analog signal,
                        You will find that it has discrete steps.

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                        • #27
                          Was gonna say, it's amazing how little resistance carbon has. I have some blocks cut out of the bottom of an old crucible, about the size of the old blue-tip match boxes. So, they are a graphite mixed with fire-clay basically. The resistance on my Fluke is less than one ohm (I use them for starting TIG welders, they don't foul up the tungsten)


                          Originally posted by Paul Alciatore View Post
                          Carbon is sometimes used in plastics for obtaining a black color. I heard a story once where an electronic manufacturer purchased some black, plastic sheets to make terminal boards for audio. They had all kinds of cross talk which took some time to trace to that carbon filled plastic. They had neglected to specify "non-conductive".

                          25 miles north of Buffalo NY, USA

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                          • #28
                            Originally posted by MikeL46 View Post
                            You might consider epoxy instead of Loctite. Loctite crosslinks tin the absence of oxygen to form a bond, unfortunately, it also melts at fairly lo temps (~300F) to release the bond. If you are using Loctite super glue, ignore all the above.

                            Mike
                            I was wondering about that when I read his comment about "Locktite" . :-)
                            ...lew...

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                            • #29
                              Originally posted by J Tiers View Post
                              Dry wood is a decent insulator, but not perfect, especially at higher voltages. Something like varnish soaked into the wood might be a useful addition.

                              I'd consider dry wood a good insulator at 240V, but might have some questions at 20,000 volts.
                              It's pretty poor at high voltages as it absorbs humidity and also has a "grain" and that's not good at all,

                              one jump is all it takes with plugs and wires and then the pattern is set - the next time is easier due to "carbon tracking" and with wood it's near impossible to "scrub" and remove due to said grain and pockets....


                              That being said - this things not going cross country and buried under a hood for full on abuse, should be easy enough for Bri to diagnose, just hope if he's going with oak that it can be seen for the aesthetic appeal...

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