OM606 glow plug change - one broke off - PeachParts Mercedes-Benz Forum

jay_bob · #1 01-20-2019, 01:38 PM

So I am the latest who has gone through the OM606 glow plug saga.

Son had car up at Clemson this past semester, complained that it was running rough for the first 30-45 seconds after cold start. He got it home for Christmas and we determined that the #5 glow plug did not show continuity. For some reason the GP light did not illuminate to throw a fault.

So I read up on all the threads and horror stories, got me a set of GPs, and got to work on Saturday the 29th of December. Former owner had changed GPs in 2011 when the vehicle had about 175k, we are now at 255k.

Drove car for several miles to get it good and warmed up. Pulled into the garage and plugged in the block heater to keep it warm. Former owner was an A&P mechanic so he added an oil pan heater, I plugged that in too. Got to work on the plugs.

Got the manifold off and started spraying the threads with AeroKroil. Waited a few minutes then started removing them. 3 of them came out fairly easily within an hour with little to no drama. 2 of them put up a huge fight but finally relented after several hours of spray/loosen/tighten/loosen cycles.

And then we had cylinder #5 the problem child. Of all the ones to be problem child this was the best possible one (except for maybe #4) as it has decent access without removing too many things (I only ended up having to remove the engine wiring harness which takes about 5 minutes). I struggled mightily for almost 6 hours before it finally had enough and I got the dreaded snap.

I knew the next thing you had to do was break off the center electrode so I got my vice grips and tried to twist it off. Well of course it broke flush with the shank of the glow plug. Crap.

So I gave up for the night and settled down to research my predicament. Didn’t want to start trying to do anything rash with a drill like the poor guy in OM 606 Drilled too deep trying to extract a stuck Glow Plug did.

I came across this drill out kit MU242 12MM BROKEN GLOW PLUG REMOVER KIT [MU242] : Baum Tools Specialty Auto Tools, Specialty European Auto Tools and it seemed to be the best engineered solution on the market. A little pricey at $498 but seemed well worth it. Not made in China, actually still made in Germany, got to pay for quality. Ordered one up and it was at my house by the following weekend.

The first thing the kit gives you is a special left hand extractor threaded socket to grasp the electrode and twist it out of there. Well I could not use that since the electrode was broken flush and I could only push it onto the electrode enough for it to stay on but not twist. What I ended up doing was using that socket as a guide for a 3/16” drill bit to put a dimple in the end of the electrode so the step drill bit would have something to grab hold of. Once I got the dimple made I pulled off the socket and very carefully drilled out about a 1/2 inch of the electrode.

Then I got the step bit and began drilling the old GP out. I used a socket and extension on the neighboring glow plug as a visual alignment reference. I had my son as a spotter in front of the radiator sighting the drill bit and the socket extension for +/-Y and I kept an eye on the +/- X. The stepped bit did a wonderful job tracking down the shaft of the glow plug even though the electrode was in the way. As I got to the threads, I was generating perfect circles.

I used a magnet to collect the shavings instead of blowing them off. I used a shop vac to finish cleanup. This had a very important advantage, the glow plug is entirely made of steel and the head made of aluminum. Any shavings that are not getting picked up by the magnet is a danger sign, you are removing head material.

So once I had drilled to the proper depth I got the tap and tapped the core of the glow plug and then fitted the shaft and slide hammer. There was just enough clearance to the inner firewall for the slide hammer to work. I did 1, 2, 3, whacks on the slide hammer then SNAP and the slide hammer came free. But there was no glow plug, only a circle of steel 7/8 around on the screw shaft.

The problem was that the tap was expecting you to go deeper than the point of the pilot drill because it assumed the electrode was out of the way and you would be tapping a hollow tube. Well I could only get a few turns into the shank of the glow plug and that was insufficient strength to grip the glow plug to yank it out.

As I began to contemplate my next steps I decided to stop there and again not do anything stupid. My sons had to get back to school so they had to share a car again (not fun). I had to work the week of Jan 7th out of town so I had to leave the car all week. Sprayed more AeroKroil down the hole and let it sit.

I came up with an idea during the middle of the week to take one of the old glow plugs, saw it off just below the threads, and use that as a guide collar to try to drill out more of the electrode. So I got home and broke out the hacksaw and after a few minutes had me a custom built guide tool.

Had to go back out of town for work again last week so I got back into it this past Saturday morning. Installed my guide and was able to use a 1/4” drill bit to perfectly go down the center of the glow plug and drill out several more inches of the electrode. I busted the electrode out of the old glow plug before cutting it so I would know how far down I could safely go.

Then there was the issue of the broken tang left when the shank sheared off after the first extraction attempt. I was able to carefully use the step drill and very very slowly shave that tang back down flush with the rest of the shank.

I then tapped the new hole I drilled in the glow plug and it came out with a half dozen hits on the slide hammer. Victory! Reamed the hole out and started to install the new glow plug.

Well then I started to thread the new glow plug in and realized it was not getting tight. Well sure enough all the drilling despite my best efforts had compromised the threads. So I now have a Time-Sert http://www.amazon.com/dp/B001ZS2BJ4/ref=aag_m_pw_dp?ie=UTF8&m=A2J41G0RQ2IUXB 12x1.25 mm kit on the way and will get that installed next weekend when I get back and hopefully get this car back together.

I also decided while I had a week of down time to pull the injectors and give them over to my buddy Mark the Greazzer (luckily he lives about 2 miles from me!) and have him tune them up. Fun story, his son and my son were randomly assigned as roommates last year at Clemson!

GregMN · #2 01-20-2019, 01:54 PM

I drilled out the glow plug body. Stepped up in bit size. My hole was not perfectly centered. On the last bit size, I could barely see the threads of the head on one side of the hole. I got a dremel bit and cut a groove in the threads until the pressure was relieved enough to rotate what was left of the glow plug body out of the head. I believe that I used a small punch, chisel, or screwdriver and hammer to chase it around and out.

So, I ended up with a very small notch in the threads of the head. Not a problem. The replacement glow plug screwed in and sealed.

shertex · #3 01-20-2019, 01:59 PM

WOW...what an ordeal!!

At 125k there is one bad glow plug the the 98 my son drives. We have till November (state inspection due) to deal with it. I will have my mechanic do (I will stick to CDI glow plugs which are incredibly easy to change). I suppose we should just replace all six plugs.

83w126 · #4 01-20-2019, 02:04 PM

The 1998 I had came with a reciept for about $2800 for a glow plug change, since the shop had snapped several and pulled the head to send to a machine shop.

jake12tech · #5 01-20-2019, 03:26 PM

^^^ 6 glow plugs for a 6 cylinder engine.

What an ordeal. Far more brave than I am. I have one plug in my om606 and I don’t have it in my to drill it. I just deal with the smoke for the first minute til the cylinder heats up.

jay_bob · #6 01-20-2019, 03:45 PM

Quote:

Originally Posted by jake12tech

^^^ 6 glow plugs for a 6 cylinder engine.

What an ordeal. Far more brave than I am. I have one plug in my om606 and I don’t have it in my to drill it. I just deal with the smoke for the first minute til the cylinder heats up.

3 easy + 2 hard + 1 that had to be drilled = 6

I’m probably going to lease out this tooling let me know if interested.

This is doable by anyone who can pay attention to detail and exercise patience and common sense. The tool is engineered to make it idiot resistant.

What condition is the broken plug on your engine?

jay_bob · #7 01-20-2019, 03:48 PM

Quote:

Originally Posted by 83w126

The 1998 I had came with a reciept for about $2800 for a glow plug change, since the shop had snapped several and pulled the head to send to a machine shop.

Dealer said $5k just to r&r the head, not including machine shop charges.

I did it for 1/10th of that. And didn’t have to pull the head.

ROLLGUY · #8 01-20-2019, 10:49 PM

I hope you put anti-seize or ceramic paste on the shank of the GP.

jay_bob · #9 01-21-2019, 06:32 AM

I used copper anti seize on the threads. Do you recommend using it on the shank too?

Father Of Giants · #10 01-21-2019, 06:38 AM

The shank as in the heating element?

jay_bob · #11 01-21-2019, 07:41 AM

Just to be clear these are the parts of the glow plug as I named them in my discussion above.

From outside to inside you have:
the terminal - that accepts and retains the vehicle wiring harness connector, this screws on to the outer end of the electrode.

the electrode - a steel rod that is concentric with the shank, this carries the electricity between the terminal and the heating element. There is an air gap between the electrode and the shank which provides electrical isolation from the shank (which is grounded).

the nut - where you put your wrench to apply torque to install and hopefully remove the glow plug later

the threads - that generate mechanical interference with corresponding threads in the head bore to hold the glow plug in place

the shank - the steel section that extends the length of the glow plug past internal engine facilities, to allow the heating element to be in its proper location in the prechamber

the heating element - the black tip that extends into the prechamber, contains the internal resistance wire assembly, used to generate supplemental heat for starting and emissions control

This assembly is placed into a tapered bore in the cylinder head. There is a shoulder at the inward end of the bore that mates with a taper on the end of the shank. This shoulder in the bore is intended to create a seal with the taper on the glow plug shank, to keep products of combustion from propagating up the bore. Unfortunately in practice, the products of combustion can get past this shoulder and travel into the space between the shank and the bore. Since this area is relatively cooler than the cylinder, the combustion products cool and condense and deposit carbon in this space.

The point of my response above is whether anti-seize should be applied to not only the threads, but also the shank, before installation of the glow plug. Hopefully to prevent the carbon from bonding between the shank and the bore, and prevent the glow plug from seizing in the head.

Father Of Giants · #12 01-21-2019, 08:27 AM

Do it. Put it on the shank.

jay_bob · #13 01-21-2019, 09:30 AM

Ok thanks

When I get back in town (yes that is a constant theme in my life) I will pull the other 5 and treat them all the way down the shank.

I have copper anti seize, is that good, or should I source the ceramic injector paste as used on the common rail engines?

ROLLGUY · #14 01-21-2019, 10:35 AM

Quote:

Originally Posted by jay_bob

Ok thanks

When I get back in town (yes that is a constant theme in my life) I will pull the other 5 and treat them all the way down the shank.

I have copper anti seize, is that good, or should I source the ceramic injector paste as used on the common rail engines?

Use what you have, but either will work on the shank. The threads, I would stick with anti seize. I believe the ceramic paste and anti seize will do the same job on the threads, but I have not tried it. I have only used the paste on OM648 injectors.

pimpernell · #15 01-21-2019, 11:14 AM

Quote:

Originally Posted by jay_bob

Ok thanks

When I get back in town (yes that is a constant theme in my life) I will pull the other 5 and treat them all the way down the shank.

I have copper anti seize, is that good, or should I source the ceramic injector paste as used on the common rail engines?

https://www.youtube.com/watch?v=QGoGQToXkXc