I just went thru the dreaded Broken Glow Plug experience and I am here to tell you you CAN come out the other side. It started as a rebuild on the injector pump delivery valves (replaced O rings and copper seals). I figured I would replace all hoses, the shut off valve and glow plugs while in there. I have a '98 E300DT with 155K. Glow plugs last replaced at 90K. No light on and live in the Carolina's but now was a good time to get it done. All went well thanks to Lightmans post and then I ran into stubborn #5. It sat soaked in Creep overnite, heated with a heat gun. Eventually you just have to reef on it and of course it snapped above the threads spinning around on the electrode. Many thanks to Len (Sokoloff), Alan Reynolds and Dick for providing very good info and a PLAN.

I used a slide hammer attached to a #10 vise grips to remove the top (hex) of the glow plug. What remained was the electrode center. I then twisted the center (with Vice grips) in an attempt to snap off this center and give me a good center hole. I had dissected a glow plug and found that the center measured 1/4 almost exactly (Bosch). also found that the electrode was fused only at the bottom. That worked well and I had a good center hole to tap. First though I worked thru a sequence of bits moving eventually to 13/32to drill out the threads (mark your bit with duct tap as not to go deeper than the threads). I then used a 7mm tap and threaded the center to take a bolt. It doesn't matter what specific size you use since you supply both the tap and the nut/bolt. I went back and forth between a slide hammer (with a bolt welded on - see pic) and the 'bolt,washer puller' that Alan describes. Assemble the puller and start at it. Initially, when you first move the plug you will hear a crack and you are breaking the neck between the threads you drilled and the body of the plug. A Ratcheting Combo wrench here is indispensible. Eventually it really got stubborn when it was sticking out about an inch. The 7mm grade 5 could not take the torque and I went thru about 5 of these as they would gall, crossthread and sieze. Tapped up to a 8mm and this eventually 'dragged' it out (see pic). As the plug moves out of the head you will have to slip a socket over the puller to allow the glow plug to move into the hollow body of the socket. I used a 3/8 inch deep 14mm socket. All of the other plugs showed evidence of anti-sieze coating on the body of the plug. This one did not and it was covered in carbon. I stuffed grease covered tissue about a third a the way down the now empty plug hole and rethreaded with a 12x1.25 (common in stock for Mac, Matco, Snap-on but not in most of the sets -around $10.00), reach down with some forceps and pull the greasy wad out of the hole. The threadings will stick to the grease. I cleaned it out good with greasy Qtips and then reamed the hole with the glow plug tool. Since the glow plugs seat at the shoulder of the tip they only need 27nm (Thanks for this info Alan). I priced a Helicoil kit and found it readily available and priced at $80, luckily I didn't need to go this route. I coated the body of each plug with a liberal but not thick, even coat of nickel formulated anti-sieze, also put a film on the threads. I reassembled all and have some additional notes:

-I first used Kerosene and then Drive up - a driveway cleaner to clean my intake - worked great.
-I used bungee cords to move the injector lines out of the way during the Injector delivery valve rebuild.
-I tried the multispline extractor 1st on the broken glowplug - waste of time plus you are 'driving' against the soft alluminum of the head. - go easy. Insanity is trying the longer fluted type of extractor on this - do not do!
-as I drilled the threads out, I check the debris with a magnet for peace of mind, go slow, use a sharp bit, and tapping fluid.
-since I emptied all of my fuel lines and replaced the shut off valve I knew starting the car would be tough - crack open the main filter and top off with clean diesel. Use a mason jar that went thru the dishwaser and a CLEAN funnel, slide the filter forward till it bumps against the radiator hose and fill. I did this 2x and then the car FIRED UP!!!

Costs:

> I bought all lines, shut off valve, intake manifold gasket, spare spring, copper seals, O rings, spare fuel line shims (didn't need) and plastic fuel line keepers from my local dealer for $210 - not bad considering that the shut-off valve is around $140.
>I sourced the reamer, multi-spline socket (delivery valves) and the 14 crowsfoot for the fuel lines at Baum for $100.
>The plugs (6) cost me 137.00 on line - Bosch
>The 12x1.25 tap cost me $10 off the Matco truck

everything else I had on hand. I didn't come across the 'impact wrench burp method' until after I had snapped off #5. It certainly is counter intuitive but makes sense. I might try it next time. Considering that these break off on MB techs regularly I am pleased with the way everything turned out. RR on the head, rebuilding the delivery valves, replacing the glow plugs, fuel line RR and the shut off valve - I figure I saved thousands. It took me around 12 hrs off and on over several days. I work slow but methodical, always a good approach I figure when aiming a drill bit at an Aluminum head.

This is a great site; lots good people with a sense of community around a shared passion that is Mercedes-Benz. Thanks for the help!

Bill

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