'95 E300D - Fully Unthreaded But Stuck Glow Plug - PeachParts Mercedes-Benz Forum

Old Barn Guy · #1 11-20-2016, 05:09 PM

I'm removing the glow plugs from my 606 engine. Three of them, 3, 4 and 6 were removed easily, as if they had been installed yesterday. Nos. 1, 2 and 5 are being difficult.

I'm working on #2 now. It appears to be fully unscrewed from the threads, but it is still difficult to turn and won't slide out. Is it possible that there is some corrosion on the shaft below the threads that is making it difficult to withdraw? The others looked fairly clean, although one was a non-functioning plug.

Anyone deal with this issue before? Any suggestions for how to resolve this?

Regards,
Tom

Jeremy5848 · #2 11-20-2016, 06:46 PM

This problem can be due to an accumulation of carbon on the end of the glow plug due to an over-active EGR valve. My '96 E300D (same engine) had one glow plug that was a little sticky but eventually came out. After disabling the EGR valve (for testing) I have not had any more problems.
As far as removing your glow plug, there are "split nuts" that you can buy and apply to the glow plug threads; this acts as if the head is even thicker and gives greater purchase in gradually pulling the glow plug out. There are probably other tools that accomplish the same thing. In any case, gentle wiggling (squirt penetrating oil in to soften the carbon) works better than hard yanking, which might break the glow plug.

Jeremy

Diesel911 · #3 11-21-2016, 07:09 PM

Quote:

Originally Posted by Old Barn Guy

I'm removing the glow plugs from my 606 engine. Three of them, 3, 4 and 6 were removed easily, as if they had been installed yesterday. Nos. 1, 2 and 5 are being difficult.

I'm working on #2 now. It appears to be fully unscrewed from the threads, but it is still difficult to turn and won't slide out. Is it possible that there is some corrosion on the shaft below the threads that is making it difficult to withdraw? The others looked fairly clean, although one was a non-functioning plug.

Anyone deal with this issue before? Any suggestions for how to resolve this?

Regards,
Tom

It is possible the tip is slighly swollen. The one in the first pic is exagerated. It does not take much swelling to make a plug hard to get out.

engatwork · #4 11-21-2016, 07:16 PM

Keep pulling, turning and spraying. It will eventually ease out.

Old Barn Guy · #5 11-21-2016, 10:45 PM

Indeed, Engatwork's suggestion above was exactly the process I used successfully. Literally just got the last of the three stubborn glow plugs removed. Once I was able to turn the plug, I just kept at it, back and forth by degrees initially, then more pronounced as it began to move a little freer. Each of the three plugs continually chattered and popped loudly as they were turned and didn't move freely until the very end.

A couple of thoughts, now that this fraught procedure is over, from a Mercedes and diesel newbie, so take this lengthy recap for what it's worth. First is that the glow plugs were stuck because of a buildup of carbon and tar on the shaft that extends below the threads--not due to the tip or corrosion seizing the threads. The tips were all straight, though some showed a little buildup of carbon. This accumulation on the metal shell, not the heating tube, made it difficult to withdraw the plug since it was in contact with the carbon on the sides of the pre-chamber. Even when the plug was turning relatively fairly freely, there was enough friction so that it could not be withdrawn, even with vice grips. See photo of plug. This vehicle just turned 135K, and there was no indication of the plugs ever having been replaced, so that's not surprising.

Once the plug was entirely unthreaded from the head but still unwilling to be withdrawn, I sprayed copious amounts of 2+2, a carb cleaner that works on carbon, around the threaded hole and just continued to turn the plug back and forth. This was a drawn-out process that took probably five hours for the three plugs. One plug eventually backed itself out as if it were threaded all the way to the heating tube. The other two weren't so cooperative.

With the plug rotating relatively freely and without the scary noises, I got a screwdriver under the hexagonal shoulder above the threads and levered on it while turning the ratchet. This eventually allowed to the plug to be extracted slowly, along with frequent sprays of 2+2. The damage to the threads in the glow plug picture was caused by the levering action of the driver.

What made this removal somewhat easier was the use of a Snap-on socket, FSMS12. This is a stubby, semi-deep socket a tad over 1.5 inches long. With my normal-sized deep socket, the ratchet would require several extensions to get it past the metal hoses, vacuum lines and wires to give it some room to turn. The Snap-on socket was short enough so that I could get a 3/8" breaker bar on the end of it and fit it between the metal fuel lines and other fittings. See photo. This gave me a surer control of the breaker bar than with a long extension and also eliminated the possibility of losing control of it and breaking something else. The socket was short enough to allow me to fit it over all of the glow plugs without removing anything. It also allowed me to slip it from the plug shoulder and move it to a new gripping point without pulling it totally off the plug.

Now to buy a reamer and some anti-seize compound and do the installation of the new plugs. A satisfying end to a somewhat nerve-wracking DIY project. Then, onward to the engine harness replacement.

Regards,
Tom

Diesel911 · #6 11-21-2016, 11:56 PM

Quote:

Originally Posted by Old Barn Guy

Indeed, Engatwork's suggestion above was exactly the process I used successfully. Literally just got the last of the three stubborn glow plugs removed. Once I was able to turn the plug, I just kept at it, back and forth by degrees initially, then more pronounced as it began to move a little freer. Each of the three plugs continually chattered and popped loudly as they were turned and didn't move freely until the very end.

A couple of thoughts, now that this fraught procedure is over, from a Mercedes and diesel newbie, so take this lengthy recap for what it's worth. First is that the glow plugs were stuck because of a buildup of carbon and tar on the shaft that extends below the threads--not due to the tip or corrosion seizing the threads. The tips were all straight, though some showed a little buildup of carbon. This accumulation on the metal shell, not the heating tube, made it difficult to withdraw the plug since it was in contact with the carbon on the sides of the pre-chamber. Even when the plug was turning relatively fairly freely, there was enough friction so that it could not be withdrawn, even with vice grips. See photo of plug. This vehicle just turned 135K, and there was no indication of the plugs ever having been replaced, so that's not surprising.

Once the plug was entirely unthreaded from the head but still unwilling to be withdrawn, I sprayed copious amounts of 2+2, a carb cleaner that works on carbon, around the threaded hole and just continued to turn the plug back and forth. This was a drawn-out process that took probably five hours for the three plugs. One plug eventually backed itself out as if it were threaded all the way to the heating tube. The other two weren't so cooperative.

With the plug rotating relatively freely and without the scary noises, I got a screwdriver under the hexagonal shoulder above the threads and levered on it while turning the ratchet. This eventually allowed to the plug to be extracted slowly, along with frequent sprays of 2+2. The damage to the threads in the glow plug picture was caused by the levering action of the driver.

What made this removal somewhat easier was the use of a Snap-on socket, FSMS12. This is a stubby, semi-deep socket a tad over 1.5 inches long. With my normal-sized deep socket, the ratchet would require several extensions to get it past the metal hoses, vacuum lines and wires to give it some room to turn. The Snap-on socket was short enough so that I could get a 3/8" breaker bar on the end of it and fit it between the metal fuel lines and other fittings. See photo. This gave me a surer control of the breaker bar than with a long extension and also eliminated the possibility of losing control of it and breaking something else. The socket was short enough to allow me to fit it over all of the glow plugs without removing anything. It also allowed me to slip it from the plug shoulder and move it to a new gripping point without pulling it totally off the plug.

Now to buy a reamer and some anti-seize compound and do the installation of the new plugs. A satisfying end to a somewhat nerve-wracking DIY project. Then, onward to the engine harness replacement.

Regards,
Tom

There is not supposed to be carbon building up between the threads and the heater element. I used your pic and the red arrows point to the shoulder that the Glow Plug is supposed to seal on.
The Glow Plug reamer does not clean the sealing area that the shoulder contacts so it would be a good idea to get a flashlight and peer inside of the hole and see if there is no carbon on that sealing area.
I am not sure what people use to clean that.

I enlarged the threaded part of your pic. If the area circled in yellow has aluminum stuck to it (I cannot tell from the pic if it is aluminum or not) that would be the area where the plug coroded to the head.

Jeremy5848 · #7 11-22-2016, 12:04 AM

You might experiment by blocking the EGR valve so it no longer dumps carbon into the intake manifold. Try it for, say, five or ten years, see if it makes a difference.

Diesel911 · #8 11-22-2016, 12:10 AM

This diagram is of an older engine but the glow plugs seal the same way on them. The red line indicates the shoulder where the glow Plug seals/seats. Only the heating element is supposed to be exposed to combustion (which would cause the carbon).

charmalu · #9 11-22-2016, 12:17 AM

I have read a lot of threads on these 60X engines with the stuck GP`s.
I do not have one of these newer engines as mine are the 61X engines.

I wonder if these plugs were removed say just before each winter to ream out the holes,
clean off the plugs and add new Aiti-Seiz compound, if it would eliviate this problem?

I know with the average owner, whether MB, Ford, Honda or what ever....
once the hood is slammed shut....outa sight, out of mind.
That is till there is a problem.

Not pointing fingers here at anyone, just thinking out loud.
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Jeremy5848 · #10 11-22-2016, 01:09 AM

Charlie, the problem is the DOHC configuration requiring a long, thin glow plug. This gives lots of room for carbon to build up and not much steel to resist the twisting forces of Mr. Armstrong. Result=snapped glow plug. A disabled EGR system is the best fix but your suggestion would also reduce the problem.

Jeremy

Old Barn Guy · #11 11-22-2016, 07:15 AM

Quote:

Originally Posted by Diesel911

I enlarged the threaded part of your pic. If the area circled in yellow has aluminum stuck to it (I cannot tell from the pic if it is aluminum or not) that would be the area where the plug coroded to the head.

As I noted in my post, those marks were from the screwdriver where I levered it into the side of the glow plug to assist in its removal. None of the plugs exhibited any problems with corrosion of the threads.

My conclusion was based on the fact even after the plug was unthreaded completely from the seat so that damaged threads would no longer be an issue, it refused to slide out, and remained very difficult to turn with the breaker bar, popping and snapping as it was moved. An examination of the plug showed an uneven buildup of carbon on the body of the shaft above the heating end and below the threads that could be felt by running a finger over it. In removing one of the stuck plugs, it finally backed out as if it were threaded down to the tip, indicating to me that the carbon might have been thick enough to be caught by the threads in the head. None of the plugs were totally clean, but the ones that were stuck showed much more carbon in this area that the three that came out easily.

In addition, the two tightest plugs, including the one that I pictured, refused, after removal, to slide back into their bores far enough to start threading, indicating interference in the prechamber below the threads in the head.

Finally, once the plugs had cleared the threads a bit, pumping 2+2 down the bores seemed to quickly free it up enough to have it turn easily, tho still needing to be levered out.

Can't say this is the case with all 606 engines, but certainly in this individual instance, neither corroded threads nor bent heating tip appeared to be the cause of the removal problems.

Regards,
Tom

spock505 · #12 11-22-2016, 08:09 AM

Someone mentioned a while back that a reamer is included with the on-board tool kit.

I must admit, both of my kits have a glow plug sized piece of aluminium but unsure if this correct or not.

Far right pocket

dieselbenz1 · #13 11-22-2016, 08:55 AM

Well done OBG! Some additional info below but somehow I think you know all this anyways.

OM606 Glow Plug removal Tips and Tricks

funola · #14 11-22-2016, 10:23 AM

A closer look at this pic tells me this glow plug was either not torqued properly or the seat in the head had debris on it, allowing a breach of combustion gas/ carbon to go past the seat and jam the glow plug body against the bore in the head. I doubt these are the original glow plugs from the factory since you said 3 of them are like this.

compu_85 · #15 11-22-2016, 10:40 AM

I saw this video last week, it's quite relevant:

https://www.youtube.com/watch?v=U9AO_cDdwS8&index=2&list=LLbjGpxeoF8uEbPzYTMiGd1g

-J