Glow plug nut locked to threads - PeachParts Mercedes-Benz Forum

PrestonEng · #1 10-08-2015, 12:31 PM

Help please. 1980 300D. Going through this car I picked up. The first few times starting the glow plugs worked fine, now a blinking dash light. Checking over the glow plugs system and getting ready for the new plugs that are in the mail I have been trying to take the nut off the glow plugs. The connection terminal and wire are twisting with the nut, looks like the whole center post is turning. Do I try my needle nose vise-grips?
I've been holding off taking the injector lines till the glow plugs get here, so not much room!
Thanks, Pete

moon161 · #2 10-08-2015, 12:53 PM

Stuff might be seized up. If you're changing the GP's, worry more about the GP wires than the plug itself. Try holding the wire w/ a pair of pliers and using an 8mm on the GP nut. If the core of the GP twists out, or breaks, no bigs, you're replacing it anyways.

PrestonEng · #3 10-08-2015, 01:30 PM

I tried holding back the ring terminal, they're twisting/bending against the force on the 8mm nut. I'm thinking that when I take the hard lines off I may get better access to use something behind the nut and ring terminal, still not much to get ahold of though !

moon161 · #4 10-08-2015, 01:42 PM

You might try getting a nut splitter around the nut. You might also try visegrips to pull the threaded post out of the GP. If they're old, this job is usually not too good for the harness. I think I've had to crimp on a few replacement terminals, not the end of the world. IDK if there is consensus on using anti sieze on the contacts or not.

mannys9130 · #5 10-08-2015, 01:51 PM

Hit it with penetrating oil. Just soak it, bust it loose, and then degrease the area afterward.

funola · #6 10-08-2015, 02:13 PM

Yeah, worry about the wire and lug but sacrifice the glow plug. Take a sharp chisel and a hammer and chop it off. The threaded electrode is soft iron and can be cut easily with a chisel.

Edit: when you install the new glow plug, use anti seize on the threads and do not over tighten. It's an electrical connection, not mechanical so a little beyond finger tight with a wrench so the nut does not come loose is sufficient.

PrestonEng · #7 10-12-2015, 08:17 AM

Got the job done. Not bad once the fuel hard lines were out of the way and I could hold the spacer behind the terminal with needle nose vice-grips. The plugs were a little snug with the accumulated carbon build up,but they were the correct Bosch so they came out ok. I had gotten a reamer set off EwBay.....way too long, I could get it into 1 & 2 cylinders but then had to cut off the reamer itself and proceed to use just it freehand. I have since drilled out one of the old plugs to make one that fits. It looks like it may not be quite square or plumb with the plug itself, maybe I'll wait till I have a drill press and drill another plug a little straighter.
Before doing the plugs they worked the first 2-3 times when I bought the car. The dash light came on for maybe 10 seconds, then the dreaded light was on for a second then flashing after starting ( a little rough starting). Now the dash light is on for maybe 2 seconds and she fires right up...no flashing ..whooopie!!

PrestonEng · #8 10-12-2015, 09:51 AM

One other note. The removed glow plugs were barely snugged tight, it took almost no effort to remove them (I think the terminal nut was tighter!), and they were all about the same in tightness/looseness. New ones installed with copper anti-seize and a little more torque.