I've got the ammeter with heavy wires to check the plugs, and the nice
Hazet socket with built-in swivel for removing and installing. I do not
have the reaming tool for removing carbon from the glow plug hole /
pre-chamber, borrowed that from a guy in NC, his name escapes me at the
I've read on Peach Parts that some have great success using an impact
wrench set to very low torque. I think this might be worth trying if one
has multiple cars to R&R glow plugs, but for just one car I would not risk
it, unless you have no time for the job.
Recommend you call Star Motors and German Auto to see if they have the
special tool kit to deal with a broken plug and how much they charge, so
you have a Plan B. Plan C would be buy the special kit yourself (about
$300 or so) and Plan D is R&R the head.
My write up on OM606 glow plugs:
Here are the key tips and tricks:
1. Hot engine. Drive the car until the engine is hot (I drove
my car for about 45 minutes, performing a few Italian tune-ups, AC blasting
on full, to get that engine nice and hot), and then plug in the block
heater as soon as you park in the work area. Hotter is better. The
block heater kept the engine temp up over 80 deg C for quite awhile, and I
think it only dropped down to about 60 deg C by the end of the ordeal,
about nine hours later. Ambient temps were about 70 – 75 deg F.
Is it a good idea to start the engine during the process, between plugs, to
keep the temperature up? Maybe, maybe not. Consider that at idle, more
carbon may be deposited in the pre-chamber and on the plugs, so that may
work against you. You would also need to leave the injectors installed.
2. Liberal use of penetrating oil. I used PB Blaster – it was
what I had. Immediately after the intake manifold is off, begin applying
that oil. I had ordered some Kano Aero Kroil, but it didn’t arrive in time.
3. Use a torque wrench for removal set to 40 or 45 Nm, gently
work them back and forth to slowly work them out. The Beru glow plug
literature says that 45 Nm is the maximum torque specified for removing the
OM606 glow plugs (12mm threads). Can one use more force? I did a
destructive test on two old Beru star-marked plugs (MB dealer parts), and
found one broke at 74 Nm and the next at 81 Nm, using MY torque wrench,
which may or may not be calibrated. Stick with 45 Nm on YOUR wrench,
unless you have a couple plugs to destroy to “calibrate” the breaking
torque of your plugs on your wrench. Some have reported plugs breaking off
at much lower torque values. Are Bosch or other brands weaker? Good
question, I couldn’t find any data to support that, but there are reports
of the Bosch plugs rounding off easily. The faces of the hex portion are
bigger on the Beru plugs. Unlike in the OM616/617/601/602/603 engines,
Beru seems to have a better reputation than Bosch plugs in the OM606.
4. Remove the injectors and apply penetrating oil to the inside
of the plugs! The first two plugs came out with much effort, over about
three hours, and the rest either would not move or moved very little (I did
not try #6 yet at this point, I decided to leave it until the end because
access is blocked by the oil filter canister and I wanted to make sure I
did not break off that plug). I decided to remove the injectors and apply
penetrating oil inside the pre-chambers to loosen the carbon on the inside.
This helped! Every thirty minutes or so, I refreshed the penetrating oil
both inside and out for all the remaining old plugs, using over half a can
of PB Blaster during the job. I made a spray tube extension with an angle
at the end to direct the spray to the side of the pre-chamber with the glow
plug. I used an old piece of plastic vacuum tubing, heated with a propane
torch until it was just soft and I could make a nice bend, and then cut off
the tube just past the bend.
Result: the #6 plug had about six hours of soaking with PB Blaster. It was
amazing how easily it came out. It came out SO much easier than all the
rest. I should have STARTED the job by removing the injectors and spraying
the penetrating oil inside the pre-chambers as well as outside. I highly
recommend this if you run into the least bit of trouble getting the plugs
to move. Note that you WILL need to change the engine oil after
contaminating it with the penetrating oil and all the carbon that you wash
out of the pre-chamber.
I was able to remove the intake manifold in about 20 minutes. I started
with the glow plug that presented easiest access, #5, using a 12mm deep
well socket and a torque wrench set at 30 Nm. I had only applied
penetrating oil to the outside portions of each plug. My engine harness
was replaced with a new dealer harness about five years ago, but I had a
LOT of trouble getting the connectors to pop off the glow plug terminals. Only
one or two came off by hand, the rest required that I lever them off from
the back side, using a tool meant for pulling interior paneling plastic
pins / rivets. The tool has a flat face that is forked, so I could fit
that around the glow plug pin and apply pressure to a good bit of the
surface of the electrical connector. Very strange! I will apply some
dielectric grease during assembly this time.
Plug #5: Very gently applying force to slowly creep up on the torque
setting of 30 Nm, the plug would only turn a couple of degrees. After the
first turn CCW, I turned it back CW, and then repeated. After going back
and forth a few times, the plug seemed to be getting tighter! Yikes! Danger
Danger! When any nut or bolt gets tighter as you work it back and forth,
it is a BAD sign, and the risk of breaking something goes up. If this
happens, stop, take a break, apply more penetrating oil, try a different
plug, keep your cool and be patient. Strangely, after leaving that plug
alone for just ten or fifteen minutes, it was looser when I went back to it.
I continued on with the CCW and CW bit, slowly getting more movement in the
CCW direction, until the plug started tightening up again! I took another
break, came back and found it loose again. I’m not sure what was going on
here, but patience and gentle persuasion were the order of the day and
those two qualities served me well.
#2 was the second plug I worked on, and it was moving about like #5. #4
didn’t seem to want to move at all, neither #3. I tried #1, and had it
moving gently back and forth, when as I was tightening it back in a little…
“CRACK!” and the wrench jumped. I was convinced I had broken the plug, and
my heart sank. I removed the wrench, cursed a bit. I regretted not making
some phone calls during the work week to see if any local shops had the
special tool set for drilling out a broken plug. I sent emails to my MB
buddies lamenting my woe. Applied sack cloth and ashes. Said a prayer
that I wouldn’t break any more plugs.
I went back to #5 and #2, and slowly I was able to get all the threaded
portions out, limiting myself to just 30 Nm. This took about three
the threaded portions of the plugs were out, more penetrating oil and grab
the plugs with vice grips and twist and pull, twist and pull, until both
plugs were out. Both were Beru star-marked. The inner body of each plug,
the last 0.5 to 0.75 inches, was black with soot. Obviously the plugs had
not fully seated and carbon was able to pack in around the body.
I decided to measure the resistance of #1, to see if the filament was
broken; maybe I could leave it in place until later? It measured about 1
ohm, which is good. I decided to see how completely broken it was to see
if it might hold together for a bit, and to my surprise it was NOT broken
and indeed was still very tight and stuck. However, it would not move at
all with 30 Nm of force.
I went back to #4. The Beru guide offers that applying 12v to heat the
plug for 3 or 4 minutes might help to loosen it, so I tried that. 3
minutes of current using a jumper cable from the battery positive, but that
didn’t help at all.
Time for plan B!
At this point I did the destructive testing referenced above, and
thenceforth I used 45 Nm as the maximum torque for removing the remaining
plugs. I also decided to remove all the injectors and soak the inside ends
of each plug with penetrating oil. I had thought of this method earlier
but never heard of anyone else trying it. Can’t hurt, right! I think it
made a big difference, and I recommend it.
The remaining plugs went a bit faster, but it was still slow patient
back-n-forth. I found that once I had the plug turning in the CCW
direction without reaching the 45 Nm limit, it was best to just keep
loosening the plug, as going CW a bit was liable to increase the amount of
force required to loosen again. Almost all of the plugs came out with a
crack-crack-crack as the carbon bound them up. Once I had them most of the
way out on the threads, I would soak outside again and then turn the plug
all the way back in, hit the inside end with penetrating oil and then bring
the plug back out until the thread were free, hit the inside again with
penetrating oil and then start the twist and pull. The restricted access
plugs were not easy, I used a pair of line-man’s pliers to grab the notch
at the end of the plug, lever against the edge of the head above the plug,
while twisting the plug with a box-end wrench.
The last plug was #6, trapped behind the oil filter housing. I had to
loosing the engine harness plastic support at that end and move it up a bit
to get as much room as possible. To my happy surprise, that plug came out
with minimal force. Soaking the inside (pre-chamber) end of the plug for
about six hours with penetrating oil made the key difference, I think. #6
showed the same carbon packing on the body as the rest of the plugs, and
none had any hint of never-seize.
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