So today I started changing the spark plugs at 9am I finished a few min ago at 2:45. I have to say a huge thank you to Acta Non Verba. I could not have done this without his help. Even following WIS there are things WIS does not tell you to do and this was one of those instances. ON EACH side of the engine there is a plastic vent line that had to be removed to get the ignition coils out. These vent lines have to be pulled backwards towards the back of the car to get them out. Also Acta explained where a bolt was that held on the wire harness on the passenger side which was not easy to find and of course had to be removed.

So I changed the plugs at 46100 miles and I will attach a picture of the old ones. They really don't look worn at all but then that was the same thing when I changed the plugs on my Maybach at 70k miles. I would say that it is good to change them so as to prevent dissimilar metal corrosion between the plug and head and get stuck in there. I also used anti seize on the new plugs as well as dielectric grease on the ignition coil boots.

Also attached are pictures of nearly all the tools I needed for the driver side (passenger side was far harder and required way more tools). I also attached a picture of how one lifts out the coils. You have to pull at each end like you can see me doing on one of the ends. It was not easy to get them off and it took a few minutes to get each one pulled up do to the boots sticking on the plugs. Finally a picture of the dreaded vent line. As I said earlier each side has one and it has to be removed to get the coil bolts out.... If that vent line weren't there the job would be FAR easier!

I dont know if I would recommend this job to someone to do unless they are very technical. While I am not a car mechanic I am an Aircraft Mechanic and I promise today that 2000+ hours training served me well.

 

Thanks for posting this. My first glimpse at oily bits. Very deep reach plug. They look like Berus from my air-cooled VW days.

 

Yea I had to use magnets for most of the work on this job from the spark plugs removal and install as well as nearly every screw since space was tight. I would use a magnet probe in one hand and the driver bit in the other. Install the screw in the hole and then immediately use the bit to get it threaded.

After some thought I can say this. Like my 15 Maybach that I would check the plugs at 50 and 60k miles and they looked good this car is the same. I would have no issues with holding off the plug change till 70k miles.

 

If all your plugs looked the same, Katie would you say that just pulling one or two that are the easiest to remove for a visual check versus total replacement is viable?

What is the recommended plug change interval anyway? I’ve forgotten tbh.

Bish

 

For the 16 Maybach that I had I did indeed inspect several plugs that were easy to get at. The GT there is NO plug that is easy to get at without removing the breather line that I have shown in a picture. For the Maybach and the GT I have read in the manual that they are due to change at 50k miles.

After seeing the plugs in the Maybach and the GT I would assume they are good for 100K miles but bare in mind that that opens the door for the plugs corroding in the cylinder head and sticking when you try to remove them. Also the coil boots stick at 50k miles so at 100k they might be really hard to get out as well.

IF you do decide to take on the job you must have a copy of WIS and probably give me or Acta Non Verba a call if you run into issues.

Katie

 

Hi Katie,

Thanks for the kind words. Yes, help anyone who wants to try, but I too put the degree of mechanical difficulty higher on this job. Lots of places where mistakes can be made. And, yes, my magnet collection got some use on this job.

I also concur with you on all the points you make in post #5.

Regarding iridium plugs - Technically, they should (could) last forever. The tips don't wear and the gaps remain pretty stable even after 100K miles. They are not like copper (fastest wear) or platinum, but for all the reasons you mention, it's good to "visit" these after a reasonable time.

I have had issues with iridium in the past (not this engine). I've had situations where a given head design and serious mods on some engines have caused a reputation of eating the iridium tips, broken off. This has happened to me on a build I did taking an NA engine to FI and the iridiums didn't even last 5K miles. Pulled the plugs and found 3 out of 8 plugs with broken off tips on NGK plugs. I had to go back to a copper/copper plug that had to be watched a lot sooner. Now, whenever I pull iridiums out of an engine, first thing I look for - are the tips all there, especially on a boosted platform. Luckily, doesn't seem to be a problem on this platform.

Here is an example of an iridium plug pulled after 15K miles compared to a new iridium (different brand). W/O the tip the gap measures .080" and, strangely enough, still fired.

 

I by the way did put Bosch part number 7434 from Oriley Auto Parts. They were about 10 dollars each with a coupon Vs. the same plugs from other places were around 20 dollars a plug. The NGK and Mercedes plugs were also around 20 dollars a piece wherever I looked. All plugs were the iridium plugs.

PS. After removing the vent lines I came to realize one of the points where oil smell can come from our engines. Where the vent line slides onto the post in the front of the engine does not look like a perfect 100% air tight fit.

 

I came close to the Bosch, but in the end, I bit the bullet and did the Mercedes OEM ones. I think I paid around $20.

Even though they are branded MB, the P/N stamped along the base of the plug is the NGK SILZKFR8F7S

I had a couple of extras. Here is a pic. You can see the MB brand and the NGK stamped in the steel base:

 

Katie22 and Acta Non Verba, Your post and Acta Non Verba’s comments here are valuable indeed! Thank you both for taking the time to document and help those of us feeling bold enough to change the plugs on our beloved GTs. Dave