Agro

Hi Guys,

I am an old Merc lover having owned a few of them over the years.

List includes

W116 1979 450 SEL ( 24 Years)

W126 1989 420 SEL (12 Years )

1989 300CE 24 (10 Years )

1989 560 SEL ( 8 Years)

1994 SL500 ( 26 Years)

At 71 I decided it was time to consolidate so sold the Harley 2008 Softail Custom, Sold the SL500, Sold the 560 SEL and in June this year lashed out and bought a 2011 CL63 AMG with only 47,000 Km on the clock.

Bought it from an old friend of mine so I knew it had been looked after -- Actually drives like new

It has only ever been serviced by Mercedes and the last service was done at Mercedes AMG in Sydney ( Yes Australia)

Well the first thing I noticed was that in was a nightmare to turn off the ECO system every time you start the car. In the end, fixed that by purchasing the Renntech Hand Held Tuner ECU Tune with the ECO disable function. Best thing ever, starts easy, runs smoother, seems to run cooler and I just love that extra HP. Overtaking is like a slingshot.

HOWEVER, I then started to get misfires on hard acceleration. Hmmm!!!

I had no idea when the Spark Plugs had last been replaced and on researching found a lot of info on spark plugs and ECU upgrades.

As I have done all of my own servicing and fault finding on all of my Mercs I decided it was time to start learning about my new toy

First decision – Don’t reinvent the wheel. AMG had chosen the Spark Plugs for this engine and I was not about to start changing the Spec without good reason

Yes the Merc Original Plugs are quite expensive but Bosch make the OEM product so I sourced the Bosch equivalent. Interestingly when I came to do the actual plug changes I found that the AMG Dealer had actually used the same BOSCH Plugs I had purchased. ( Naughty Dealer not using the genuine Merc Parts)

Now comes the fun and the reason for this post

In my research I noticed the Mercedes Service Bulletin that referred to the requirement to index the Spark Plugs for the electrode position in relation to the Injector location. And I also noticed the reference to the damage caused when using NGK Plugs that were not indexed. Hence my decision to stay with the Bosch Plugs

I decided that I would check the existing Spark Plugs as I removed them to check the Indexing. To do this I marked my Spark Plug Socket in the 12 o’clock position and then removed the first Plug. I found that the Indexing was about 25 Degrees before the 12 o’clock position. Continuing on I found that all of the existing Plugs were in a similar Indexing Position.

That made sense because I assumed that AMG would machine each spark plug thread in the same index position for the same batch of heads in manufacture. Similarly if Bosch were making the Plugs to Mercedes Specs then I would expect all of the plugs in a given batch to torque up to a similar position.

SO if I wanted to move the Indexing position up the 25 or so Degrees to achieve a 12 o’clock position what were my alternatives??

First I checked the sealing washer thickness on both the old and the new Plugs and to my surprise I found that they were all .058 to .059 inches thick. I put one of the new plugs in and torqued it up to Mercedes Specs. Guess what , exactly the same 25 Deg before 12 o’clock position

Ok for a 14 mm Thread on the plugs they have a pitch of 1.5 mm which means for a 360 Deg turn the plug would go in an additional 1.5 mm

Converting that to inches I decided to Sand down one of the old washers about eight to ten thou and see how far that realigned the index point.

Next challenge – How to hold the washer whilst sanding. Fortunately I have a 3D Printer that I have been using for over five years, so I printed up a small holder with a recess to hold the washer whilst sanding

So a Cutting board, a piece of 220 grit Sandpaper and a washer in my 3D Printed holder and I could now sand the washer evenly to any desired thickness . After a bit of experimenting I found that with my Spark Plug Sealing Washers sanded down from their original 58 Thou thickness to 48 to 50 thou I could get all of my plugs to index within Plus or Minus 2 Degrees from the ideal 12 o’clock position

NOTE !! Very Important -- When Sanding place the rounded face of the washer into the holder.

When finished place the washer back onto the Spark Plug with the sanded side towards the Spark Plug ( ie away from the engine) The sharper edges of the sanded surface help locate the washer centrally on the plug for perfect sealing

I will be interested to follow

a) Continuing Engine Performance

b) Service life of these plugs given the optimum positioning

Please note that in accordance with numerous comments about Spark Plugs on ECU Modified Engines I have reduced the Spark Plug Gap to .025 Inch for my testing

So far I am impressed, vehicle starts easily ( Could Just be the new plugs), Engine is running smoothly in all rev ranges and no misfires.

I have my fingers crossed

Now for those of you who are interested in doing the same thing I have attached a photo of the washer holder I made. I tried to upload the STL file ( 3D Printer file) for the part but the site would not allow this file format. If anyone wants the file to get a washer holder printed locally if you leave me a message with your email address I can easily email it to you.

By the way the process of removing the Spark Plugs is a whole other story but for any of you older Merc owners out there a small hint. Remember the Instrument Cluster Removal Tool that we all either bought or made ( I have a 3D printed Handle file for that too) , well I have found a new use for it. It is perfect for hooking under the Spark Plug Boot Tab to allow you to put upward pressure to remove the Spark Plug Boot. Apply pressure slowly and be patient – They will pop off .

Second important point on Spark Plug removal -- Jam a towel down in the gap between the body and the motor to catch the tools and the plugs that you may drop in the tight working space. After doing the first bank I had to jack up the car and remove the under engine panel to retrieve three short extension bars and one of the Ignition Coil securing bolts that got away. I learnt the lesson and used the towel on the second side – Much easier retrieval

Ok guys that’s my story so good luck and I am waiting to see how long it takes for the NGK enthusiasts’ to try this on the colder plugs to get the right indexing

Keith

jvakos

Hi @Agro Keith - fantastic write up thank you for sharing this as I am about to tackle this job on my 15 E63.

I know your a CL63 (same M157) and would assume if you posted to the W212 E63 forum where there is much more activity and interest in this plug indexing topic you would get a zillion likes and thank you’s!

I have had NGK 1555 plugs for 12k miles on an AMS 100 oct tune (car has 48k miles) which are long over due now to be replaced and I decided to go with MB OEM plugs this time which I believe you did also….

Did you change the gap on your OEM plugs or leave it with the factory gap? Any misfires to report all all has been good?

https://mbparts.mbusa.com/oem-parts/...lug-0041598103

Agro

Hi JVakos, No I did not use the MB Plugs, I used the Bosch plugs and yes I did reset the gap to .025 Inch.
I have now done 28,000 km on these plugs with no plug issues. I have however had an issue with a coil pack. Kept getting a misfire on No 2 Cylinder. I found a wreck of a 2016 SL with same engine and very low km and bought a couple of plug packs and replaced No 2 — Problem solved.
What I did notice is that MB had changed the coil pack design for the later models and the housing around the plug is much more robust. I broke the housing on two of my original ones just getting them off the engine.
The new design is so much stronger so I went back to the wreckers and bought the other six coil packs for spares ( Haven’t needed them yet)
Also one other really important point. MAKE SURE YOU PUT FRESH “DIALECTRIC GREASE” on the rubber boots for the spark plugs each time you take them off. The grease is cheap and the boots will come off the plugs so much easier if you do.
Good Luck with the plug change and don’t forget to plug that gap between the engine and the body with a towel before you start. It will save a lot of swearing.
Regards
Keith

jvakos

@argo Keith you're a prince thanks for all the feedback and nice score finding those coil packs off that SL in the wreck. I have 8 new coils from FCP euro which were about $45 each and they have a lifetime replacement warranty which for this part is pretty helpful since coils on tuned M157's seem to degrade around 5000-10000 miles max from my experience but my AMS tune is pushing 20-21 psi so all that heat is clearly not good for coil longevity.

Thanks for the tip about the MB grease for the boots and I just bought some from Amazon for $10 bucks!

I also bought this 14mm spark plug socket with swivel that a few forum members said works great for reaching the #4 and #8 rear plugs and also picked up some varying length extensions so hopefully I'm equipped to tackle this job )

Ill try to document the install and how the indexing went and hopefully I figure this out and start doing these plug changes on my own since the tune is forcing me to swap the plugs around 5000 ish miles. I have always had my indy guy do plug changes for me for around $600-$700 each time with plugs and labor so saving some $$ here and assuming i do this correct it will give me peace of mind knowing the index is set propertly!

thank you again!