I removed an old glow plug, which I suspect as weak, from my 85 300SD. The old one came out uneventfully. On trying to install a new one I just can't seem to get the threads to engage. I looked in the hole as best I can with an inspection mirror and I can't see any bunged up threads. The threads on the old plug show no signs of damage. The threads of the new plug look good. Any hints as to how to go about getting this thing in?

Yes. I am turning it clockwise and it is square in the hole.

What is the best way to chase the threads without pushing debris into the combustion chamber?

I aplogize for the silly sounding question, but I fooled with this *&##%$ thing for an entire hour last night without success!

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1985 300SD, 203,000 miles, dark blue

Lil Sarah says: "Poor old Grandma Blue Car...She's sad."

don't worry about tiny flakes of carbon. take an old toothbrush and grind down the stem under the bristles, then put it in the hole with some kerosene. Rotate and brush around. Crank engine over a few times. This creates a powerful action blowig any debris OUT. Now look carefully at the threads from the new and old glowplug. Wirebrush and clean the old one first, and try to reinstall by fingers. If this goes easily, I would look super close at the new plug. If not, I would look super close at the threaded hole with a small inspection mirror ad strong flashlight. NEVER use a wrench to get the plug started, always by hand. This is especially important for things like glowplugs and spark plugs. I learned this many years ago with sparkplugs. Don't ask how

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

Take your tap and gob stiff grease into the threads and ' evacuation lanes' ... then you can run it in there and the small stuff will come out with it...
If your corresponding piston is in the wrong spot in the otto cycle you will suck stuff into the precombustion chamber instead of spitting it out by turning the engine...

Try putting the old plug back and see if it goes back in smoothly. If it does than there may be a problem with your new plug. Try a different plug.


Phil

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'95 E300 Diesel, 264,000 Miles. [Sold it]

I did look at the threads as best I could manage with an inspection mirror prior to my first post. I could see not obvious damage, but it is a small hole and the threads start a ways inside. I cleaned the internal threads last night as well as I could with a toothbrush, as Pete suggested. I can just start the plug in by hand but I need a wrench to turn it from 1/2 turn onward. I am still unsure that I have proper thread engagement.

I picked up a 12-1.25 tap on the way to work this morning. I will try chasing the threads tonight. I initially hesitated to try that because I could see no good way to remove any chips I created and the idea of having an unknown number of cast iron chips bouncing around in my combustion chamber was not appealing. The idea of using grease in the flutes to hold the debris is clever. I will do that. I will also try using a drill bit to remove as much carbon as I can.

The old plug is also hard to get started, as is another that I have on hand. I assume I just have a problem with carbon buildup. The old plug squeaked like a dry hinge with every turn of the wrench while I removed it.

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1985 300SD, 203,000 miles, dark blue

Lil Sarah says: "Poor old Grandma Blue Car...She's sad."

continue to approach this issue with great care and caution and your success is nearly guaranteed. Upon reinstallation of your new glowplug I would heartily recommend the use of anti-sieze compound. It will prevent the problem in the future. Good luck, Ray

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

I finally got the new plug in last night. The bad hole was #4, behind the injection pump. I had to cut most of the shank off the tap to get it into the hole. I wasted some time trying to grind uniform, parallel flats for a wrench, using a Dremel tool. My bench grinder motor is fried. Then I realized I could just use an 11 mm open end wrench to turn the tap by slipping it over the teeth.

In a twist, typical of my auto repair adventures, I lost one of the nuts that hold the wires on. It dropped behind the IP and I could not find it. I drove 7 miles to Home Depot and found 5x0.8mm nuts in the metric fasteners bin in the hardware section. Great. I saw they also had 5mm wavy washers, so I put the nuts back in their little bin for a moment, picked up the wavy washers and decided to get them as well, in case one of those was lost. I hate making 2 trips. I picked the nuts back up, stood in line the requisite 20 minutes behind a guy buying $900 worth of house paint in 1-gal cans and drove home. When I put the first nut on, it hung up after going on about 1/2 turn. I looked at the bag: 10-24. SOB!

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1985 300SD, 203,000 miles, dark blue

Lil Sarah says: "Poor old Grandma Blue Car...She's sad."

well, you're not alone!

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.