[W126 Coupe] Fouled Spark Plug

[Chet Hwilka]

Pick up a “spark plug” socket from your local auto parts store.   It has a
rubber sleeve inside that holds the plug in so you don’t drop is as you’re
removing it.  There are basically only 2 sizes, large and small (I think ¾ &
5/8 inch). You want the large one.  You may also need a few extensions and a
swivel for you ratchet, some plugs are hard to get to.

Take your time removing the plug and if it becomes harder to remove as
you’re unscrewing, stop and screw it back in a bit and then go back to
unscrewing.  Repeat until you get it out.  The threads sometimes get gunked
up and you don’t wanted to force anything and possibly strip the threads in
the head.  The plug is steel and head is aluminum.  When you reinstall,
clean the thread and hand screw the plug in and just snug it up with the
ratchet.  Do not over tighten or you may strip the head.  And never use
power tools on spark plugs.

Depending on the mileage, you probably have a worn valve guide not just the
seal.

 

Chet

 

  

 

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From: mbcoupes-bounces at mbcoupes.com [mailto:mbcoupes-bounces at mbcoupes.com]
On Behalf Of Henry Viveiros
Sent: Wednesday, September 01, 2010 5:24 PM
To: 'Mercedes Coupes Mailing Lists'
Subject: [W126 Coupe] Fouled Spark Plug

 

My 1991 560 SEC had been running rough and the dealership diagnosed the
problem as a #4 fouled plug that may be caused by a valve seal. They cleaned
the plug and things seem to be OK. Is the #4 plug on the right or left side?

My question is: can I remove the spark plug and clean it every once in a
while—I’m really not into taking the engine apart to replace the valve
seals.

When I look at the spark plugs I can just see the tip of the top and not the
part that the socket would fit on. Can I just slip a socket onto the plug to
determine the correct size to use? I haven’t been able to “feel” if I am
actually on the plug or not. Am I likely to cause any problems (breaking the
plug)? I don’t want to cause any more problems than I already have.

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