I made my own by taking a 7mm drill bit and drilling out an old glow plug. then set the length at just past a new glow plug and welded the threads to the drill bit. Now I just thread in till it bottoms out the threads. I ream out any time I pull a glow plug, as it only takes a few seconds and they come out much easier and cold starts are much better after reaming.

__________________
Von
Fairport, NY
1973 Unimog 416 Doka
1980 Unimog 416 Doka
1981 Unimog 416 Doka
1984 Euro 280CE w/diesel conversion
1985 300TD Estate wagon
(I really need to stop buying these things!)
http://vonsmog.com

If you're gonna make one, a drill bit is the better way to go.

1. You drill the hole in the glow plug with the same bit

2. It has more chip clearance than a reamer. I.e. it can hold more carbon.

3. A drill bit cuts into the carbon better than a reamer.

__________________
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

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

__________________
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 .

__________________
-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.

Use of the vehicle is definitely another factor.
If the car gets long distances at higher speeds, like my 240/300 cars do-- probably not an issue.


Each one of my cars gets at least one 1000 mile trip per month, except the HMMWV engine in the truck, but that one gets periodic multi-thousand mile trips.


I worry more about carbon buildup in the gassers that are not used so much, or the 1950 170D

__________________
Strelnik
Invest in America: Buy a Congressman!

1950 170SD
1951 Citroen 11BN
1953 Citroen 11BNF limo
1953 220a project
1959 180D
1960 190D
1960 Borgward Isabella TS 2dr
1983 240D daily driver
1983 380SL
1990 350SDL daily driver alt
3 x Citroen DS21M, down from 5
3 x Citroen 2CV, down from 6

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.

__________________
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.

Attached Thumbnails

 

__________________
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.

Attached Thumbnails

 

__________________
84 300D, 82 Volvo 244Gl Diesel

"The" reamer, no, but something that accomplishes that purpose, very much so.

__________________
'82 300CD
"Pearl", the very first turbo diesel 123 coupe
Totaled 11/23/18, rebuild in progress.
'85 300TD, "Artemis".
'78 300D euro, "Ol' Red", mostly retired.
'85 300D, "Gandalf".

So we have come to the conclusion that a 7mm drill bit is better than a reamer??

__________________

It is one of the items that works.

__________________
84 300D, 82 Volvo 244Gl Diesel

I'm happy I'm so rich I can afford Kent's reamer. One of the luxuries in life a millionaire can apparently afford which is evidently out of reach of the little guy

- Peter.

__________________
2021 Chevrolet Spark
Formerly...
2000 GMC Sonoma
1981 240D 4spd stick. 347000 miles. Deceased Feb 14 2021
2002 Kia Rio. Worst crap on four wheels
1981 240D 4spd stick. 389000 miles.
1984 123 200
1979 116 280S
1972 Cadillac Sedan DeVille
1971 108 280S

A drill bit isn't better than a reamer. Spend the actual $50 on the Hazet reamer. If you don't want the plugs to eventually weld to the head and break, get a reamer. If you're selling the car and don't care about the next guy have at it. Cutting corners on a drill bit instead of buying the tool that is designed for your engine to me is bizarre. You got a Benz why not spend the money and do it right. Especially an old antique like a w123. I'm all for custom tools and stuff but with something like that, do it right and spend the money on the right tool.

__________________
Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
2008 Chevy 3500HD Duramax 340k
2004 Chevy 2500HD Duramax 220k

Only because pretty much everyone on here says they use a drill bit and not a reamer

__________________