Mercedes-Benz W123 Project: Glow Plug Replacement
 

Anyone got any questions on the Project: Glow Plug Replacement for your Mercedes-Benz W123?

Here's a back link to the original article: Pelican Technical Article: Glow Plug Replacement

-Wayne

Hey Wayne, thanks for the how-to! I don't have a reamer tool...can't I just use a wire brush instead?

Jim

I first came to this forum because it has the Wikipapers. They helped with change of the fan clutch, the glow plugs, and the fuel lines. When I have questions, I get answers within an hour or so.

PeachPartsWiki: Do It Yourself Articles - Mercedes Vehicles

I have a '98 e300. I have to do a fair number of things myself so I can afford to keep it on the road.

Thanks.

I use a drill bit.

Perfect! Thanks!

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Jim

A little white lithium grease on the bit or the reamer catches the carbon. The drill bit turned by hand not in a power drill.

Excellent! Thank you! Will be doing this job next week. Based on reading resistance from the relay plug wire, I have two glow plugs out for sure. Engine is really hard to start below 50 degrees F. Hopefully I don't have a fuel problem as well. Seems like three cylinders should be firing but they don't seem to be hitting like they should. I get .6 ohm resistance on those three wires but the #2 and #3 cylinders are open (full resistance with no electrical flow). When the car finally starts it blows a lot of smoke. Runs okay after it gets going. Will two glow plugs out make it that hard to start? Thanks for the info!

Yes.

I have a reamer I can pass on. Used once for the 5 glow plugs on my ‘85 CD. You can buy it and then pass it on. PM me if you’re interested.

Since that article, there was some dispute by one guy here about the need for reaming and how to do it (claiming I was an idiot, etc). Turns out that OM617.952 engines vary. In at least one of mine (1984 & 1985_CA), the pre-chamber is fully exposed when you have the fuel injector out, i.e. the pre-chamber is a straight cylinder going down, with no throat. I had no trouble running a tap thru the glow-plug hole to clean-up the threads, though I have found even that isn't needed. Sounds like earlier pre-chambers w/ a throat can build-up carbon in the lower part. During that back & forth, I posted links to photos from an old post where a guy showed the different pre-chambers. If anyone wants to pull that info together and add to the DIY, have at it.

I never said you were an idiot, just that a tap to clean the threads is way different than a reamer that cleans the glow plug chamber, so you can't say they're the same and that "reaming" doesn't accomplish anything based on your experience with "thread chasing."

http://www.peachparts.com/shopforum/diesel-discussion/377501-following-exact-glowplug-reamer-my-84sd.html

-Rog

I just put two new GPs into the old beast and what a difference lol. It starts right up now! I guess I figured out how to diagnose which GPs are bad. Checked resistance from the relay plug. #2 and #3 were dead. All the others clocked in at .5 ohms. Those two are semi-accessible, so I didn't take the injector lines off...just cussed a lot. Did #3 first since that one was easiest. Drill bit didn't pull anything out. I used one size larger than the diameter of the GP tip. Since that one was so clean and since my hands were taking a beating getting shoved into those small spaces, I neglected to ream #2. Sometimes ya gotta say screw it. Thanks everyone for your help!

My point is that later OM617 engines have a cylindrical pre-chamber with no place for carbon to build-up. There is no throat as in the drawing linked in post 11. The pre-chamber is 1-piece and has straight walls. If you want to clean-up the threads in the glow-plug hole, a standard metric tap will work. But, I didn't find any carbon on the threads, so seems a waste of time. People don't normally chase spark plug threads in gas engines, which is about the same issue. Anyway, would be great for someone to search and grab the photos of different pre-chambers and add to the DIY for posterity.

That doesn't work me for diagnosing bad plugs. It always reads open loop on everything.

My drill bit had quite a lot of room inside the GP hole. It didn't feel like it was a narrow throat like in that drawing.