I think what he is saying the STRAP Can't be in the 90% in front of the injector...
I think this also means that that the open face can be outside of the 10:30 and 1:30 as long as the strap isn't in that 90 giving you 270 of "good"..

From what I UNDERSTAND from the bulletin the OPEN face should be in the 90% 10:30 - 1:30 for proper indexing-- giving you 90% of good as @5soko highlights.. but what do I know..

Torque spec is your friend. Too much overthinking on this thread. Buy MB parts and install them according to MB specs.

yes, i agree with this, this is what i understand aswell.

https://cimg9.ibsrv.net/gimg/www.mbw...661632ffa2.png

you are correct, I stated it backwards.

You had me second guessing myself for a second lol

Just using Merc plugs and torquing to spec totally did not work in my M278 engine.

Bought 3 sets of plugs. 9 Mercedes branded plugs from FCP Euro, a few of the same Mercedes labeled plugs from my local dealer, and 9 of the same part number with Bosch labeling.

ALL OF THEM indexed wrong. ALL were aiming at about 7 o'clock. (well,.. I only tested 2-3 from each set) Whereas they need to aim between 10 and 2. (The open end of the ground electrode)

You CANNOT just put them in and trust they're right,.. and you also should never trust this job to a dealer or an indy. I asked 2 indy's as well as the tech at the dealer about indexing plugs,.. and all had a puzzled look on their faces. I don't think any of them had any idea what I was talking about. The one tech said they use Merc plugs and just torque to spec. And admitted he had never checked to see if that produced a correct result.

It MAY in your engine,.. but it didn't in any cylinder in my 2012 car.

Now,.. the original plugs DID. And I hear from Eurochgarged, FCP Euro and others that after '12 they realized the plugs were a tad hot,.. and the plugs used thereafter were a bit cooler.

Did the heads change for 13? Did the threads on the plugs change when they made them cooler? I don't know the answer,...

threads are still the same. I use the colder plugs(NGK-97506) and they are close...but I always order extras, just to be safe. I have a record of 4:5 being correct.

Yeap - Indexing is important and while I understand people that say stock this and stock that I really APPRECIATE YOU but this conversation is for those who want to push the limits and figure out how to do it in the best manner possible.

Conclusion in my mind is - stick to spec but verify -- now that I understand the indexing fully I'll try going back to NGKs because I feel I had better performance with those bad boys when I didn't have misfires (Which I think I finally resolved)..

Great thread, great info.. Thank you all.

Agreed, this is very informative. Thanks TECHNICIAN, nota_amg, and Duckstu :y

Plugs
 

Anyone know the difference between the ngk 1555 and the 97506? Ngk says the 1555 protrudes about 2.7mm more than the 97506

I'm back hahaha. Installing step colder plugs as I'm going s2 next week, and so far 3 plugs I tried will not index properly. Will try my 4th and if that doesn't work I will reinstall the oem ones gapped at 0.022

I just did a 2014 E550 and the Merc plugs that were in there (at 55,000 miles) were all over the place,. AND NONE OF THEM were aiming within 45 degrees of the injector. Most aiming down at 7 O'clock.

The new Merc plugs I bought from FCP Euro, as well as the ones I bought from my local dealer were also aimed down. Totally acceptable.

Same with the Bosch version of the same plug.

Yes 23 nm is the torque spec,.. but installing factory plugs and properly torquing them WILL NOT cause them to be installed correctly.


This is NOT a job anyone should ever let a dealer or an indy attempt. There is about zero chance they will do it correctly.

I bought 4 sets of copper washers off Amazon trying to get washers that were 12mm ID x 16mm OD and 1mm thick (12 x 16 x 1). Only one set were actually 1 mm hick. The others were 0.7 or 1.5.

With that set I was able to get 4 or 5 of them to be within spec.

I sanded down a Bosh 1.5mm wsher to get the rear-most cyl on the driver's side close,.. and the front 3 on that side are almost withing spec using 1mm washers.

On the notepad below I recorded the before and after (before being the arrows inside the circles,.. and after being the arrows on the exterior of the circles).

. The 1mm washers corrected the pass side bank nicely,.. but only managed a slight improvement in the left bank. The rear most cyl I sanded down,.. but really needed to do all 4 like that,... or find some 1.3 mm thick 12 x 16 washers. Need to buy 3-4 more sets I guess and keep measuring.


https://cimg8.ibsrv.net/gimg/www.mbw...225c29f9cf.jpg
.

Here's the washer sets i have. The ones in the set with the red arrow are the only 1 mm ones I have found so far.

https://cimg2.ibsrv.net/gimg/www.mbw...bb84edb47b.jpg

I just reinstalled the oem plugs, gapped them to 0.022 and torqued to 23nm and all of them facing towards the injector.

With the Ngk step colder, best I could get is 6, meaning the back of the plug was facing the injector, so I gave up after trying about 4 diffrent plugs

I spent an hour or two the other night sanding down stock plug washers from 1.5 mm to 1.2 to 1.32 mm and then re-index'd the driver's side bank. Got them all well within spec.

Arrows INSIDE the circles were how we got the car, presumably with orig plugs.

Black arrows outside the circle were after we changed them, and used 1.0mm washers on 7.

The red arrows are my 1.2 - 1.32mm washers.

Looks like 1 mm gives almost a full rotation. Perhaps 340 degrees.

Going from 1.5mm to 1mm allowed the plug to index clockwise almost 1/2 turn.

Hopefully that will help everyone know what thickness washers they need to custom make.

https://cimg5.ibsrv.net/gimg/www.mbw...c1b76acf20.jpg

So adding a 1mm washer made all the Difference?

NO,

REPLACING the 1.5mm washer that comes on the plugs with one that is 1.0 or 1.2, or 1.3 is what did it.

The problem is,.. it's very hard to find a 1.0mm thick 12 mm x 16 mm copper washer, (The one set I pictured above had them, the others lied) .. and it's impossible (so far as I know) to find 1.2 or 1.3 mm copper washers.

So you have to make them.

Ah i see 👍

I just re-did the plugs in my 2012 E550.

Previously I had found that both factory and the Bosh branded plugs index'd at about 7 -o'clock,... so I closed the gaps a bit, sanded the tips clean, and re-installed them.

Last night I installed a new set, and found that they all wanted washers in the 1.15mm - 1.2 mm range. (Stock washers are 1.5 mm)

And sanding down the stock washers presents a bit of an issue, where the washers no longer have a curved surface where they meet the head. And with a now wider and flatter mating surface, they won't crush as much. I.E. they wont continue to rotate as much when you torque them to spec.

So I beveled the inside edge a bit with a Dremmel, and beveled the outside edge with a belt sander,.. so that the mating surface would be narrower, and I could still get a good crush.

A lot of hassle.

Arrows on the inside of the circles are where the original plugs from late 2011 were (on my M278 2012 model year engine).

Arrows on the outside of the circles are where I ended up, and the washer thickness I used to get there. Thinner makes it move clock-wise, thicker moves the ground electrode counter-clockwise.


https://cimg5.ibsrv.net/gimg/www.mbw...4269a7d365.jpg

Has anyone noticed a difference in the way the car runs after indexing? As described this is quite a bit of work for what may be intangible gain. I like the idea, it has been done for decades, but is is worth the effort.

Well it's something the amg engineers said needs to be done and guess makes sense. Then again, bunch of direct Injection cars on the market that don't need indexing that run fine, including bunch of competitors like the m5

That might be quite a project.

Any differences most of us notice are more likely from the plugs being new..

Someone would have to put their car on a dyno with new indexed plugs, run it, then, while still strapped to the dyno, swap in similar new plugs, poorly indexed, and perfectly match the operating temps and run it again to find out.

The dire warning in the things from MB is about how it's critical to have the correct temp plugs and have them correctly indexed,.. or else (with pic of burned piston).

Who's to say how much of that damage was from incorrect heat range, and how much if any from the indexing.

I looked at some of my piston tops with a bore-scope while I had them out, and they all just looked a bit sooty. Less so on the '14.


For sure back in the day we'd get power out of our 2-strokes by indexing plugs. Perhaps it's worth 8 hp?

Translation: "If an owner tunes, let the buyer beware." LOL

Si latine uteris, recte fac:

If an owner tunes, est ludus eorum.

My "grammar nazi" lesson for the day. :o:

So much effort and as pointed out above, nearly no one knows how to do this properly. Has anyone seen any failures or damage from not correctly indexing plugs?

In a tuned engine, with upgraded turbos, internals, WMI, etc., such as I'm currently doing on mine (Weistec W.4, complete) there are factors introduced which make indexing much more critical than in a stock motor.

1) EXCESS HEAT. This requires using one step cooler plugs to avoid high risk of detonation, which can be catastrophic.

2) TONS MORE FUEL. It's required in order to produce up to 1050 horsepower, so in order to burn it all efficiently, without fouling the plugs, they MUST be indexed.

There are lots more factors introduced with major mods, but there's no need to write a book here. I was just indexing my plugs on Friday, using NGK Iridiums with the heads off it's super easy. However, no washers needed to be changed. At 23Nm they all fell in the perfect range.


https://cimg2.ibsrv.net/gimg/www.mbw...98f24daee5.png
NGK Iridium 1X Torqued to 23Nm. Supplied washer.
https://cimg3.ibsrv.net/gimg/www.mbw...e029a93925.png
NGK Iridium 1X Torqued to 23Nm. Supplied washer.