Tackled this a few weeks ago, finally got around to posting the video.
Hope this helps you guys, do me a favor and hit the thumbs up thanks

I watched it. I already did my plugs change, however didn't pay any attention to the indexing, just did 23tq and .25 gap and no problems noted.... so far. (200 miles already)

Ha, I watched this before I even saw the post. I have new plugs and coils sitting in a box. My plugs were done right at 60k according to records and I am at 100k. So I guess I feel like I can drag my feet. After the explosion, did you notice any difference in performance or smoothness? I have been meaning to take mine for a ride with Xentry connected and monitor for misfires (I don't think it has any but want to see what the ECM thinks).

@kennyd thanks super helpful video (once again!)!! so many M157 owners pulled their hair out trying to understand why the MB OEM plugs don’t index exactly correct without sanding the washers as you showed which gives them enough additional “turn” to get them from 9’oclock to finally pointing toward 12’oclock at the injector.

Hey how did you get the washers off & on the MB OEM plug with out damaging the threads? I am a novice admittedly but i couldn’t get mine off easily so I gave up and just installed the NGK 1555 plugs which indexed nearly perfect with just 23NM of torque and nothing else. I’m keeping the MB OEM plugs at $25 each for the next change and will try the washer sanding

Best spark plug video brother. Always look forward to your videos. Super explanatory

I got lucky as I just started My plug swap the day Your vid came out. Thanks a ton. You convinced Me to go ahead and index the plugs as I go. I have a question for anybody or all. Are the sound deadening foam pieces that needed? They seem like a heat trap to Me plus 2 of the 4 clips broke during extraction.

i have to figure out how to unscrew the washers too on the oem

Edit*** you have to gently use some pliars to unscrew the washers. They come off very easy

Disregard My question about the foam inserts I see now it's to insulate the fuel rails.

2 plugs into this operation. I started in the back on pass. side #4 I believe. The original MB stamped plug was 90 deg. off from the injector. Cylinder walls look clean. I got the replacement to around 10 deg. Off the injector.#3 MB plug was 180 deg. off injector, yes pointing straight down. Ugh. The scope showed 2 black streaks on walls. Must be scoring, I expected it to not be so dark colored. There is still crosshatch visible in both cylinders. I am still working on indexing #3 new plug, had to stop for other stuff.

I was wondering about this, if anyone had experienced any issues if plugs etc not indexed correctly…

First off, this is an AWESOME video. I love watching people work on these cars.

i have customer cars that were probably never indexed correctly since they went to colder plugs. Their cars still run, hilariously although no tuned car making actual power will have the startup of a stock car anymore. I have serviced SO many out of warranty AMG's at this point that I can tell you they're not even indexed this way from the factory, from the dealer, and I'm aware of it enough to torque it properly and get it close but anything further than that I might as well not drive Mercedes anymore. When I refer to indexing I literally mean just torque it to factory specs, every other plug before DI I was just doing it til I felt the washer bottom out.

The washers themselves aren't even to within that level of accuracy and everybodys threads are different. That and there is a TON of slop in your conventional shelf grade socket. I use SK sockets so I get a better fit and they last a little longer but nobodys tools are even that accurate. A torque wrench with any extension isn't even accurate anymore.

I'm certain these are the original plugs at 50k. A little disappointed at the 180 deg off plug. But it still runs. Hopefully get the rest tomorrow

OK finished this project up today. Only 2 of the factory installed plugs were within 45 deg. of vertical. 2 were 180 deg off. Now they are all within 20ish degrees of the injectors. All of the new copper washers were .061-.060 thick. In the end I needed ,045-,050 so I pretty much sanded and filed for a long time. The plugs were at 50k The startup afterwards was noticeably quicker and the idle was noticeably smoother. I replaced all the coil leads as well , all of the originals shredded during removal. I had to get quite medieval on them with angled extra long needle nose. I am missing several small chunks of skin on various parts of both hands but it's done.

The spec is +/- 45 degrees. No socket is so bad that you couldn't achieve this spec. If you weren't sure, all you have to do is after torquing the plug, wiggle it to expose the play. Observe the line you drew and see if that line is roughly in the middle of the play. If it is, good enough. And even if it wasn't, it still would be within spec...

With the thin walled 12 pt 14 mm spark plug socket there is no play. The spark plug fits in so tight you can get Your index line inside 45 deg.

since Kenny was nice enough to do this for us. Doing the washers head of time might save us the extra trials of on and off

Thx man

Expect to wear off all your fingerprints sanding them down LOL

I will note, you notice that my numbers were very consistent from side to side, but they were both different from side to side. I assume this is just differences in machining and making the heads. I don't know if it's going to be consistent for every car and every year. In fact I would imagine that there might be some variances from head to head.
I would hate for someone to sand all these down to find out that theirs were backwards for mine etc

I am gonna measure mine and see how close they are stock to these

kenneyd is kenneyDIY, with a big CAPITAL D

Thank you for another great one!

I’m on a stage 2 tune. I want to try the NGK 97506’s. Thoughts?

i have a AMS 100 octane tune with the NGK 1555's colder plugs and they worked great... no misfires until i got long overdue 12k miles running them on the tune and finally changed them and the mis-fires went away.

when I installed my NGK 1555's with 23NM of torque they indexed within spec at either 11 o'clock or 1 o'clock without any messing around with the washers

bought them from Rockauto for $13 per plug also

I heard some mixed reviews about ngks colder step ones. I had those and returned them and bought the oem ones. Hope they work out for you

I see tuned guys running the 1555’s and others running the 97506’s. I ended up getting the latter. Guess we’ll see if my car likes them.

I have the exact same tune as @jvakos dyno'd on the same dyno tuned with same tuner and same intakes (bb) on OEM plugs and gap and no issues for 6k+ miles ... go figure

Not surprised. I honestly don’t know the state of my current plugs so I just picked up this set in case they need changing. Figured if I’m gonna go through the trouble bore scoping, then might as well change the plugs while I’m at it.