# spark plugs



## chuck foster (May 19, 2008)

i was asked by a member here to provide some more info and pictures on the way i make spark plug so i figured i would share this with everyone.

i start off with a piece of hex bar stock for the metal part of the plug






i then thread the plug body to suit the engine, in this case it is #10-40 tpi.





i then make an adaptor to thread the plug body into so i can hold it in the lathe a bore out the body for the corian insulator.





i use an end mill to counter bore for the corian body 





this next pic shows the corian loctited in place (loctite red)





i then drill a .031" hole from one end of the corian to the other and loctite a piece of .031" spring or piano wire
in the hole. this wire will become the center electrode.i leave about 1/8" of the wire sticking out of the top of the
corian insulator this is where i solder the brass plug wire terminal on.





i then make a copper washer from some copper tubing that i got from a plumbing supply place.
i just part them off on the lathe.





the last picture shows a finished plug with a ruler for size reference.





i hope this helps anyone interested in making spark plugs (speedy)  
in another post i explained why i choose to make them.
it was mainly because some engines need a long or short reach plug, so as to get the spark right in to the combustion
chamber. another reason is some times on a small engine the bigger plug look out of perportion to the rest of the engine.
i have run this type of plug in several of my engines and had very little trouble. when the plug gets dirty you just take it out and rub the business end on a piece of fine emery paper to clean it.

thanks to all who read this and i hope it was informative.

chuck


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## Mcgyver (May 19, 2008)

Chuck, great write up - thanks!


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## Lew Hartswick (May 19, 2008)

I guess with that size plug a side electrode is not needed. It is a "surface gap" plug my Saab 850GT 
used surface gap plugs but they were a LOT bigger.  even took a bigger socket than normal plugs.
  ...lew...


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## cfellows (May 20, 2008)

Chuck, thanks for the write-up. Good information!

Chuck


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## TinkerJohn (May 20, 2008)

Great tip on when to drill the hole for the electrode. I've always drilled *before* gluing the two parts together and have broken my share of insulators! I will try this and will bet I won't be breaking as many now! Thanks for the details and pictures.

TinkerJohn


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## Stan (May 20, 2008)

I see that you leave zero clearance for the loctite around the center electrode. Do you also leave zero clearance between the metal body and the corian?


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## chuck foster (May 20, 2008)

thats a good question stan..............i had to go out in the shop and do some measuring and i found that i leave 1 or 2 thou. clearance for the corian. if you make the hole the same size as the corian it can become very difficult to press the corian in to the metal body and corian will break easily if you push too hard. 

thanks for all the positive replies guys, it makes this a much more enjoyable hobby if we can all share and be positive ;D

chuck


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## Speedy (May 20, 2008)

Chuck, 
that was great, pics and written  
cleared up allot of Qs. thanks man :bow:

I was told another good substitute for Corian is Macor (mica filled ceramic) the Corian is good for low heat engines while the Macor holds the same heat as normal ceramic found in spark plugs (more for higher rpm/heat) carbide tooling machines it. 

Chuck now you got me thinking of other ways (yours is great, not taking away from that :bow. to bad I dont have a lathe/mill yet. sending you another pm. ;D
thanks for taking the time for the pics for use to see. very much appreciated.


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## Stan (May 21, 2008)

Thanks Chuck. My home made spark plugs have been pretty much of a disaster so I will give your method a try.
Stan


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## chuck foster (May 23, 2008)

one thing i forgot to mention is that i owe all of my success at building spark plugs to a guy who lurks around here from time to time but never posts anything.

this gentleman's name is ed erwin ........... a very good model builder and a wealth of information that he freely shares with anyone.
ed if you read this i thank you very much for all the info and the many good times we have shared in this great hobby :bow: :bow:

chuck


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## Powder keg (May 26, 2008)

I have always wondered how "They" did that) Thanks for sharing.

Wes


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