spark plugs

vilanar said:
On Navarro and Offy heads that I have B6L plugs are too short and very prone to fouling .....
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Some of the modern heads now have 3/4 reach plugs - which is a VERY good thing. This gives you much better plug selection as well a a lot more threads to work with. If I was buying new heads and could select a year/model that had these long reach plugs - that is definitely the direction I'd go. Great example - the recently re-released Edelbrock block-letter 39-48 heads . . . now have 3/4" plugs (great enhancement for sure!).

I've never stripped the threads out of any 3/4" reach spark-plug aluminum head - flathead or OHV, but I've had to fix a bunch of vintage aluminum flathead heads with stripped out plug threads.
 
Measure the length of the threads - if they are closer to 1/2", then you may want to find a 1/2" reach plug - as the B6Ls are 7/16, just like the Champion H10s. You can also chamfer back the last few threads in the heads or 'fire slot' the plug area . . .

Old article with a few part numbers as well:

http://www.btc-bci.com/~billben/headprep.htm
 
Bored&Stroked said:
Measure the length of the threads - if they are closer to 1/2", then you may want to find a 1/2" reach plug - as the B6Ls are 7/16, just like the Champion H10s. You can also chamfer back the last few threads in the heads or 'fire slot' the plug area . . .

Old article with a few part numbers as well:

http://www.btc-bci.com/~billben/headprep.htm
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I'm surprised to see this suggested here. Why would someone cut up an original set of heads when it's so easy to just go out and buy a set of plugs with the proper reach? The engineers who designed these heads put that extra reach into their original design to gain holding power for the plugs in aluminum, which is not as strong as cast iron. Not only will this weaken the heads, but the plug will still be in a less than optimum location. I am using a set of "Edmunds Custom" heads because the plug location. A little initial initial checking showed that these heads were designed to use 1/2" reach plugs rather than 7/16". There are literally billions of 1/2" reach plugs floating around out there. A few folks have mentioned aftermarket heads designed for 3/4" reach plugs. Visualize a 1/4" chamfer in a set these heads with the plugs shrouded by an equal amount. I's not a pretty sight.

Bite the bullet and spend the time and money to get the proper plugs.
 
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JWL said:
I did a search for USA manufactured spark plugs and "no results found". Maybe I didn't ask the question correctly.

I have never had a problem with Champion plugs. I'm not sure why they are out of favor. Perhaps the (I think) Mexican manufacture location?
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John,
I changed from Champion H10 to NGK due to the Championship fouling really quickly then after they fouled the damn things wouldn't fire again! NGK had no such problem. Didn't know they were made in Mexico. They went out of favour with me because they were rubbish. Haven't run champions since then, but that was 12 or so years ago. Maybe there better now?
Martin.
 
The thread depth on my heads are .600+ close to 5/8". I don't plan to modify the combustion side of the head.
 
big deuce said:
The thread depth on my heads are .600+ close to 5/8". I don't plan to modify the combustion side of the head.
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I'd definitely look for 1/2" reach plugs. Here are a couple part numbers that should work well:

NGK 7534 B6HS
Autolite 425
Bosch 7902 WR8AC+ Super Spark Plug
Denso 4012 W14F-U U-Groove Plug
Champion 896 L90C Racing Plug

If it was mine, would try the NGKs - have had really good luck with them in general (race engines and the street).

B&S
 
Choosing a spark plug is like a political debate, You need the right reach plug, with the right temp range, and most of all, never seize on the threads. Back in the day when aluminum head first caber out, the Champs were prone to stripping the threads. I understand that was because the had cut threads instead of rolled threads. Not sure if that's still so. The never seize will help prevent that. They also require the proper torque, which I call just snugging them down. With all that BS said, I prefer the NGK plug.
 
Wow, this like asking what oil to use. So many "suggestions" it will get you dizzy. If your plugs are fouling, most times it is not the plug. Carb problems or ring problems that can't be cured by new plugs. JMO
John
 
John,
I get what your saying, but when I had champion plugs fouling and then quitting soon after, the NGK worked perfectly. Didn't foul, and kept on firing. In my mind that is a spark plug issue, as by just swapping plugs, the problem dissapered.
Martin.
 
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Well after doing some bench work, I came up with a solution; for my heads anyway. Ended up using NGK .750 reach plug br6es B=14mm, R=resistor, 6=heat rng, E=19mm reach, S=standard center electrode. At first it put the plug too deep in the chamber, but found some Arp hardened washers .120 thick that made the end of the plug flush with the chamber and no threads showing. The OD of the washer sits perfect inside the spark plug pocket.
 

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