[updated:LAST EDITED ON 18-Jul-02 AT 08:50 PM (EST)]Aw heck, I don't know where to put this tidbit or warning, so I'll put it here.

After about 5000 miles on my sidegapped, and wider-than-stock-gapped Autolite plugs (5125's?) I decided to change 'em out today, and this is what I saw:

You know how the tips of plugs, or the end of a distributor rotor gets all rough after being used (sparks arcing and the transferring of electrons)? I had that effect on the side of each center electrode. But this was bad... this was on the bottom half to two-thirds of the center electrode, and was in a small area (let's say it only went ~ 1/6th or 1/7th around the total diamter of the electrode).

On top of that, the 'rough' areas never coincided linearly with the covering-electrode! On some it was at the nearly total opposite side.

So I had a good spark jumping from the base-side of the center electrode to some part of the head in each cylinder (probably the same part(?), but the way each spark plug was facing (they weren't indexed) determined where the spark jumped from the center electrode at. or that is what I'm guessing...)

The tops of the center electrodes were not rough at all. This could mean the plugs weren't firing from the tops much, or that the severe roughness that was on the side of each electrode happened during a certain changed condition (like the rare times the MSD-6A sparks would stop being multiple sparks and became single "lightening bolts" past 2500 or 3000 RPM - this is a rare condition in daily and highway driving of an 4.9 inline six).

But that is my experience for those who have MSD's and/or side gapped plugs and Inline Sixes - or whatever combination led to my strange findings.

I kept them, but do not have a camera to take a close macro picture of the effects to show you guys. Sorry.

 

Why the MSD on an I-6? Do you have other performance mods? If so, are the Autolites the stock plug heat range or different?

 

Why not a MSD-6 on an I-6? Better spark is better spark, no?

But the spark plugs are the stock heat range - I admit I should change 'em, but haven't got around to looking up the right plug number yet.

Have you got info I could use, or are you just bustin nuts on people who don't have V-8 envy?

 

 

Is the MSD wired up right? When I worked for Bosch, I learned that the spark is designed to jump from the outer electrode to the center one, so that wear is always on the outer electrode to allow for easier adjustment and prevent the center electrode eroding inside the insulator. On some 70's and 80's Japanese motorbikes and Citroen 2CVs, where the coil was double-ended (no distributor), one plug would wear normally and the center electrode on the other would start to erode as described above.

We used to see this on some old vehicles where the ground was positive instead of negative and the coil was wired in reverse to modern practice.

 

Thanks for the trivia - always interesting to know what I might be facing.

Well, I used MSD's wiring harness, and the negative and positive leads go right to their respective battery cables.

I guess I'll pull a plug or two out soon and check how the new ones are doing.

 

You are only supposed to take about an 1/8th inch off the ground electrode. Any more and the spark can jump all the way to the shell with a hot dog ignition system.

 

I have to admit i probably took a little more off the electrode than that (I side-gapped the plugs before the MSD-6A was installed), but even then the tip of the (cut) electrode was still closer to the center electrode than were the sides of the plugs.

But I'll bet you're right - after all, we are talking about a large amount of voltage and current, so the relatively thin side-electrodes may have more natural resistance in it than did the very sides of the plugs (which were in direct contact with the head, and that would seem to make them the 'best' conductors (or recievers) of the spark).

Best,