Strange spark plug wear in 2.2 engine

[Black 993]

I've got the engine out of my 1970 911T for some transmission work and I'm also doing plugs and valve adjustment. I was surprised to see the condition of the plugs. 1 and 6 have quite worn center electrodes. Detailed pics below. I'm wondering what the group thinks is going on here. Plugs are NGK BP6ES.

This is a low-mileage engine I rebuilt myself 10 years ago. Stock displacement, only mods are Mahle S p/c's, mod-Solex cams, and an MSD CD box (ignition stock otherwise except for re-curved distributor). Runs well, doubt I have 10k miles on the engine, plugs probably have less than half that. Carbs are in good shape (Paul Abbott did the rebuild at the time). Admittedly it's been several years since I did any real maintenance on this car as life and kids have been very busy and it does need the float levels and carbs dialed in better.

From L-R here are plugs 1-3 -- you can see how worn down the #1 electrode is.



From L-R are 6-4. #6 has the most wear of any plug, it's almost flush with the ceramic.



Detail on 1 and 6:

[Magyar Kiwi]

Hi
Are the manufacturers markings the same on all 6 spark plugs ?
Maybe this:
Counterfeit Plugs: Counterfeit NGK spark plugs (often found through unofficial online marketplaces) can result in using inferior materials that wear out much faster than genuine NGK products.
Cheers

[Black 993]

Yup, markings are all the same. I had a similar thought about counterfeit parts. But they sure don't seem like anything other than real NGK's. If they're knockoffs, they're pretty good ones.

[buster73]

Looks like normal wear but very surprising after only so few miles. Also strange to see such a huge difference between the cylinders. Probably just the wrong heat rating for your modified engine. NGK classic proposes BPR9EIX for the 2.2 S-engine. Of course gap will be too big with the worn down center electrodes, which can in return accelerate the wear process.

[dennisO]

I wonder if just got some bad plugs?

[Richey]

I'm thinking the same thing , this is not from wear .

[PeteKz]

I'm thinking the same. Did you check and gap the plugs when you installed them? Are you sure?

If that was electrode erosion, the top electrode should be badly eroded too, and it's not.

[Black 993]

Oh yeah, gapped them carefully. I wonder if it's from the MSD box?

[PeteKz]

If the MSD was causing it, it should be the same on all the plugs.

[brighton911]

What strikes me as strange is there is no particular erosion on the center electrode, the sides are fairly straight, not rounded. Looking forward to the solution to this one, I have no ideas other than what others have stated.

[john walker's workshop]

EDM by MSD is my guess.