Changing plugs on 112 engine
 

I have a 98 C280 with 40K miles and the V6 112 engine I was told by the dealer it needed new plugs and was thinking of trying it myself.
When I looked it over I see the plug wires are terminated in a metal boot at the plug end. Before I did any damage I was hoping I could get some advice about whether this is the "normal" lifetime of these plugs and if so do these plug wires simply pull off is is there some trick to removing them
Thanks
Bob

Hi:
Yes, all 112/113 owners of this vintage should really take note here. The service life of the sparkplugs is 100,000 miles OR 4 years. Lots of these cars were built in 97 and have been in there for the 4 years, and they do turn out rather hard after 4 years, did a set on a car just like yours last week, we charge book time of about 1.5 hours, depending on model (chassis).
In general what needs to be done is remove the engine trim panel (over the intake manifold), and remove the screws from the center of each coil on top of the valve cover. Pick the screws out of the coils with a magnet so you don't lose one, but DON'T ASK HOW I KNOW THIS!!!! Then the coil wires are removed. I recommend removing them just on the spark plug side, the wires will also pull off the coil side (by hand), if this appeals to you. Ultimately you only need to remove the spark plug side. You'll see there are 2 plug wires per coil, one over the other. The top coil wire goes to the FRONT of the engine, the bottom one towards the REAR. Also disconnect the small electrical connector from the coils. To get the metal end off of the spark plug, the recommended tool, per Mercedes, is a 17mm wrench which was originally used to adjust valves on an older Mercedes, the engine type escapes me now, as does the part number of the tool. The 17mm end slips into the indent on the end of the metal cover, and the wrench is then pried against the valve cover to pull off the end, works slick. On the ones that I have done, some of the plug wire ends weren't very accessable by this wrench anyways, and with some effort I was able to twist and pull the end off of the plug anyways. DON'T pull on the wire itself, obviously.
I recommend the Mercedes plug for this application, as I recall they retailed for about $11 each, you need 12 of them on a 112 engine (280 or 320), 16 on a 113 (430). Gap is 1mm and please do use a torque wrench to tighten, 28nm is the spec.
Gilly

Yikes! Quite a job compared to the leisurely 15 minutes to reaplce the plugs on my M111 engine...

Thanks I'll give it a try
Is this the tool they recommend ?
Thanks again
Bob

That is a valve adjustment tool. I use a Snap-on spark plug wrench for doing these. BE CAREFUL!

Another question re plug gap
 

Gillybenztech said the gap is 1MM and the plug box says the same . Yet the Owners manual specifies .8mm is this wrong??
Also the photo I attached was in reference to the wrench to pull the plug wires off not change the plugs
Thanks again
Bob

Yes, the owners manual is wrong, the box is right, the gap on the 112/113 engine plugs is 1mm. I have noticed the owners manuals being wrong a time or two on tech info like this. The spec had been .8mm for so long some guy who is in charge of what goes into the owners manual probably refused to believe it was different!
This whole tool for removing the spark plug boots I knew would cause some confusion. I can try to remember to post the tool number. It's not a socket like what you posted a picture of. It's a wrench, it's 17mm open end wrench, probably around 12" long with 2 pretty tight angles, like for clearing obstacles. The open end of the wrench will engage into the "groove" in the metal end, then the handle of the wrench can be pried against the valve cover to pry the end off of the plug. Easier to do than describe. If I had a digital camera I would post a few pictures of how to do it. Maybe I'll ask for one for my B-day this year or something.
Gilly

Great thread! Thanks for the tutorial.

Have a great day,

The tool number (this is the tool per Mercedes) is:
110-589-01-01-00
Original application is 110 engine valve adjustment.
It's made by Stahlwille.
We still show it as available, retail should be about $27.
Gilly

Thanks
I'll get one
for anyone interested there is a picture at http://www.samstagsales.com/images/hz2771.jpg
Bob

Yep, that's the one!
Gilly

Bob,
Want to sell that tool ?
Arthur

Arthur
I'll let you know after I change the plugs. I'm considering making one after seeing the picture. Given the best price I could find was $40
Bob

I was asking about the valve adjust tool that you posted the pic. of. I think I wrongfully assumed that you had one on hand.
It fits my 113s [ if it's the 14mm one] and they are nasty to do without it.

Anyone else have one for sale, I would be interested.
[ specially if they no longer have use for it]

Tnx

Bob:
The tool number I gave still came up as a good number on our parts dept. computer, retail was, as I said, about $27. Run the tool number past your dealer and see what they come up with.
Gilly