So, I have a GX head bought from an indvidual that had shimmed spark plugs in it. They were shimmed at the base where they screw in. The reach of the tip ends up back in the hole where the electrode is and does not extend into the combustion chamber. Does anyone know the logic behind this?
Spark plugs that are in the head: NGKB9EV
Factory plug should be NGKBP5ES.

Thanks in advance,
Kelmo

Normally i would have called this indexing the plark plug, but it doesnt normally entail the plug to be lifted out of the chamber.

The idea of indexing is to direct the spark towards the inlet of air/fuel this can create a better fire in the chamber.

If plugs arent indexed the electrode can theoretic sheild the spark as a worst case senario.

Having the plugs out of the chamber can in terms reduce the compression ratio. I use to machine done the washers on 50cc 2stroke pocket bike engines to get a little more compression

Cheers
Jake

Is it these things?

No, they just used copper washers about 1mm thick at the base of the plug where the threads start. I'd post a pic but the batteries are dead....dang.

they might have used the shims to stop the electrode contacting the piston? depends on how much the head was skimmed as to whether or not this is necessary.

Thats the only logic i can find behind it.

Why don't you ask the guy why he did it etc???

Sounds like "indexing". They idea is to get all four spark plugs pointing the same way.

Of course regular plugs use a gasket, but you are seeing something other than that, right?

Due to the head having B9EV plugs I would say it was used for competition or something along those lines, these plugs would typically foul up if it was just for street use.

1mm washers would still be just in the realms of use for indexing the plugs.

Ronald: I did call the guy but did not hear back from him. Hindsight being 20/20, I should have asked when buying but am learning as I go and didn't know what to ask..dang.
DD: The original gasket (ring) is gone and the copper wahsers are in place of it.
All: I think at this point indexing was the prupose as this engine was supposed to end up in a competition car, so that would put MLS dead on, nice call.
Me thinks stock plugs will be going in....after we measure to make sure they dont hit a piston...
Thanks everybody

Kelmo

It seems that this is definitely an indexed set up for the plugs, because the plug style has also changed. The original plugs are BP's, with the P standing for protruding, where the electrode extends out from the plug, while the fitted plugs are B9's, with the electrode in the body of the spark plug. Also the plugs are pretty cold, which means they'd foul up easily. Do you know what size the combustion chamber is & what's the compression ratio? Could be a small combustion chamber, which meant they had to use B9's, which meant they had to be indexed to get it to burn the mixture.

Dang, I wish I was smarter.
I get the indexing part, but the electrode part of the plug was still back up within the hole that the plug goes into.
The block is bored 0.40, pistons are flat.
As far as size of combustion chamber and compression ratio....this kid ain't that smart.
But I did learn about the "P" in NGK plugs today.
Thanks,
Kelmo