Spark plugs
 

I have a 59A stock engine, 6 volts. My question is: Has anyone use a Chevy spark plugs. They both are 18mm threads. The Ford (Champion)
H-10 threads are 11mm long. The Chevy (Champion) J-12 threads are 9mm long. The H-10 porcelain is receded in the head, as the ignitor is flat with the surface of the combustion area. The J-12 the threads are short of bein flush with the combustion surface about 3/32", but the porcelain and ignitor protrude into the combustion chamber about 3/16 of and inch. Seems the J-12 plugs would burn cleaner at slower speeds.

The reason I ask is, the plugs always look black, like the are not firing hot enough, or long enough.
Thanks
Bill Herbert

Re: Spark plugs
 

Most plugs are designed per the manufacturers specs for length of reach, type of sealing surface between head and plug, and the desired heat range. If you want a colder plug or a hotter plug, there are designations for that. If the reach it too long, it can lead to detonation or after fire dieseling. If the gasket surface isn't the same it may not seal well or damage the faying surface. Almost every plug ever made has at least one step up or down for heat range which is reflected by the part number.

Champion H-10 is only one usable brand. Autolite, NGK, and Bosch all make equivalent plugs for the flatheads. Some are better than others. Fuel system problems or piston ring problems can also be the cause of sooty plugs.

Re: Spark plugs
 

I'm aware the manufactures design and make a spark plug for each engine. Thanks.
I was just asking if anyone has adventured into using a different plug as described.
You advice about detonation is something to consider.
Probably will re-use the H-10. Doesn't hurt to inquire about peoples experiences.
Thanks for the reply

Re: Spark plugs
 

Just to stir the pot, I had a '51 276" Merc all built up in a '36 3-Window. I had an MSD ignition and Offenhauser heads. I found some surface gap plugs from a 2 cycle outboard motor that were perfectly flush with the inside surface of the head. They worked perfectly. I don't think I would have tried them with a stock ignition. I am currently building a 258" 8BA that I am going to run Edmunds heads on. According to "Ol' Ron", Edmunds moved the spark plug just enough to allow the use of an extended tip plug. We'll see how it works out.

Re: Spark plugs
 

I've read many posts on here regarding plugs and based on that bought NGK. I am very happy with their performance, as is a good friend with a 40.

Re: Spark plugs
 

I made a drawing of various plugs fitted to an Offenhauser head to help in picking something that would fit best. Can't help with heat range.

Re: Spark plugs
 

Very interesting!

Re: Spark plugs
 

Thanks for the input. One of the reasons I'm interested in information and experiences is because the H-10 plugs were engineered for the needs of a Flathead and the "GASOLINE" we use to have. With todays "formulated fuel" I don't think the H-10 is totally efficient.
Thanks

Re: Spark plugs
 

My experiance has shown the best plug to be the NGK which offers two heat ranges. Any Champion plugs I have treid in the past which come from Mexico were easily fouled even on a stock flathead.

Re: Spark plugs
 

I am with adlieo, the ngks are great,car never ran better

Re: Spark plugs
 

18mm thread ??

R

Re: Spark plugs
 

I didn't want to admit it, but after seeing Tubmans response to using Mercury surface gap plugs, I too have to admit doing the same thing. The plugs were spares out of a 2000 Mercury 90HP two stroke. The engine is 286", B&M supercharger with MSD ignition. It ran great on these plugs but I got concerned about long term effects and removed them for Autolite 216s.

Re: Spark plugs
 

I've used Champion RJ14YC plugs for years in my flatheads. The longer snout stays cleaner, even in loose engines.

Re: Spark plugs
 

Yep, it's interesting that "hotrodcbx" was kinda reluctant to admit he used surface gap plugs. My lifelong desire was to have a '36 3-Window with a "3/4 race" Merc and hydraulic brakes. I drove the car as a "daily" for about five years until a local "rich guy" made me an "offer I couldn't refuse". I never replaced any plugs, and it ran as good when I sold it as when I built it. He later sold it to some guy in New Zealand for a lot more than he paid me. Any of you "Kiwis" know about a "Vineyard Green" '36 3-Window that came in about 10 years ago?