Indexing Plugs?

[jreiley]

I assume that to index plugs in an engine, you true to orient the electrode the same in all cylinders. If I am correct, is there an easy way to do this seeing as how the headers block seeing the orientation of the plug.

[johnracer]

The most important reason to index plugs is to prevent the piston dome from contacting the ground strap on the plug. If you don't need to do it, it isn't worth the effort. It usually doesn't matter if the ground strap is up, toward the front, or toward the rear, just not down.
I use a sharpy to draw a line on the porclain on the ground strap side so I can see the orientation with the plug installed & tight. It may take a bunch of plugs to get a full set indexed without index washers........
Johnny

[jreiley]

The obvious question is what are index washers? Thanks for the sharpie tip.

[johnracer]

You can get indexing washers from Jegs, Summit, ect. They're basically a shim that goes on the plug seat to change the position of the ground strap. If for a tapered seat plug, they're cone shaped, and flat for a gasketed plug. They look like a gsket and come in various thicknesses......I prefer to buy several sets of plugs at a time and find the correct one for each hole by trial and error. It can take a while and be kinda frustrating, but it beats smashing a plug at high rpm....the washers work fine though. I just don't like the idea unless I'm in a hurry.....or already tried 20 plugs and still haven't fould one that will work!!

[hammertime]

I use indexing washers seen no difference in doing it this way or buying several plugs and doing it that way. I put mine between 10-2 o'clock

[jreiley]

It would seem to me that the use of diamond fire type plugs, that have 3 electrodes, would negate the need to index plugs. Have you ever tried these plugs?

[johnracer]

Nope. I'm not a fan of "trick of the week" anything. You'd be money ahead to stay with a conventional plug in my opinion.....if they have 3 regular ground straps, they may hit the dome no matter how you index them.

[jreiley]

Good point.

[chevyfireball]

I bought a Moroso indexing nut. You just screw in an old plug that you know is indexed for a certain cylinder, mark the position on the nut, then find a new plug that screws into the same position. The nut is good and wide so you can mark a scratch on it and a cylinder number. A hell of a lot easier than indexing on the cylinder itself.

Another reason for indexing, other than piston to plug clearance, is to ensure the spark is facing the gases and the strap is not going to interfere with any ignition of the gases or flame travel.