If someone chooses a drill bit that is too large to fit in the hole and they are unable to figure that out, their life is probably filled with "bad effects." They should leave the hood in the closed position.

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

If your going to do the job, DO IT RIGHT!!! Its like a guy doing delivery valve seals using a torque wrench by feel instead of using a proper tool.


https://www.youtube.com/watch?v=4i7GerLZxRY

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96 E300d

Thanx for all the good replies .

I have a set of reamers, I hope one is the proper 12 X 1.25 MM .

I too was lazy and didn't do this important service when I replaced my glow plugs, as mentioned normal carbon buildup causes shorter glow plug life although you may it have had it yet happen .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Not to stir the pot and say you don't need to- but on my '83 300d with 250k+ miles (broken odometer) and an entirely unknown maintenance history, i did not ream the holes. All of my glow plugs backed out with no issues, as with going in. i had two dead plugs- one that simply would not glow at all and one that the end melted off of and destroyed the prechamber and injector. I believe the prev owner said he used ether to start it so maybe that did it.

I watched Kent's video. Looks like he copied Mercedes's (poor) design of using a reamer as the cutter instead of a better design- a drill bit. A drill bit will cut into the carbon better and funnels more carbon into the flutes. A reamer will tend to push more carbon into the pre-chamber. This is my opinion of course.

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Just my opinion.
Actually the stock mercedes type reamers have been doing their job for a long time now. I have never seen a thread on any of the Mercedes forums that I used to visit where someone had issues with the Stock type Glow Plug Reamer.

As you thread the stock reamer in the the crud gets pushed to the rear and there always seemed to be extra room in the rear when you were done.

If you think the older stock reamers were not effective look at the new Hazet ones that are likely a lot more expensive.

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84 300D, 82 Volvo 244Gl Diesel

When I made and sold Glow Plug reamers in the past (I don't do it any more) I found a reamer that was not only cheaper but had more cutting edges, flutes (grooves) land a spiral. In the pic you see the reamer, my version of the Glow Plug Reamer, a Glow Plug and the stock type Glow Plug Reamer.

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84 300D, 82 Volvo 244Gl Diesel