NOS Spark Plugs

[Jerry Wieland]

I recently purchased at auction an inventory of motorcycle and automotive parts including a stock of NOS spark plugs. Is there a reliable source where I can find out the application for them without searching an entire catalog.

Thanks Jerry

[chuckthebeatertruck]

No.

The problem is that application catalogs, even when digitized to easily search, may not be accurate.

Im betting you know this, so, I’m writing for future searches on the topic.

Basically, plugs came in more reaches at different times than we often realize and different makers liked different things, especially prewar and before alloy heads. As the correct reach plugs went obsolete, the shorter reaches were speced. You can’t crash anything into a shorter plug. Longer plugs on vintage machines often fit but the protruding threads carbon and can tear the hell out of threads coming out. The downside of shorter plugs is that while they work, they sit in a hole and the spark is shrouded,

Bike may actually be ok, but still runs a bit odd and fouls plugs too often just cause the darn plug sits in a hole. You find yourself carrying spares. . .then, you machine a short plug to the right length and often that same old bit of kit wakes up and chuffs merrily.

So, unless you know the bike’s oem reach, you may/may not match in reality.

And, not all application catalogs list reach, so it’s not always apparent if/when a sub happened.

Then there’s heat range or “grade” which, isn’t even close to uniform across the industry.

[T. Cotten]

It gets worse, Chuck,

When producers like NGK redesign tried and true vintage-application plugs like their A-6 as resistors.

And not only fail to tell anyone,

But then deny it to your face!

....Cotten

[PRG]

Howdy chaps,

Nothing wakes up a later model Chief like an extended tip plug, I’ve run NGK BP7ES’s with half an inch of the threads turned off in several of mine for over 30 years. Couple these with a simple Hall based electronic ignition like Clyde Crouch’s and you have a far cleaner running more responsive machine. Due to high crankcase pressures required for the lubrication system to work, any ring wear leads to oil burning and plug fouling thus requiring the band aid compromise of short reach plugs such as the Champion J6C. Build your motor with a focus on the best bore RA, minimal piston skirt clearance, use of modern gas expansion based, rather than tension, rings and that propensity to oil burning will be mitigated.