Should I remove the pre-chambers? - PeachParts Mercedes-Benz Forum

Dudernio · #1 12-12-2013, 06:07 PM

I'm pulling the head off my OM603 1987 300SDL with the #14 head. I suspect either a cracked head or blown gasket. Is there any reason to pull the pre-chambers? Will anything be revealed by doing so? And if so, is it wise to pull them while the head is still attached to the block?

It has been consuming coolant steadily over the last year, I would fill the resevoir about every 500 miles. The top radiator hose always pressurized after the engine cooled the next morning. Finally one day after a long drive, when I went to restart the engine it would not turn over due to hydro lock.

sixto · #2 12-12-2013, 06:41 PM

Consider that you need a special tool to remove the lock ring and a special slide hammer to remove the prechambers. Given that slide hammering is involved, the block provides a good work bench. It sounds like you need a new cylinder head. If so, you'll probably find a used head with valves and prechambers. If you buy a new head casting, you'll have to move the good valves and springs. The #14 prechambers can be trimmed to fit the a later casting so you can keep your inejctors.

Sixto
87 300D

Diesel911 · #3 12-12-2013, 07:27 PM

Myself an one of Our Members removed the Prechambers in a Parking Lot on a Head removed from the Car to salvage the Prechambers from a cracked Head.

I supplied the Tools and the Slide Hammer (has a 5 pound wight on it). I don't know about Hood Clearance but it would have been easier to do both removing the Retaining Rings and the Prechambers with it on the Engine.

The Retaining Rings that go in the Aluminum Heads have a deeper threaded area and Aluminum is kind of grabby.

With the Head off of the Car one of us had to stand on the Head in order to get the Lide Hammer and Puller to work.

This other example was on a 671.952; when I pulled the Prechamber it peels crud off the outside of the nose of the Prechamber when you pull it and that stuff drops inside.
In My case I made sure the Piston was at TDC or close to that.

Compromise. When you pull the Head off do an inspection for crackes and if you can warpage. If it looks OK leave the Prechambers in place.
If you need to pull the Prechambers put the Head back on the Engine and tightend down some of the Bolts/Nuts; enough to hold the head down to help remove the prechambers.

jt20 · #4 12-12-2013, 08:44 PM

Quote:

Originally Posted by Dudernio

I'm pulling the head off my OM603 1987 300SDL with the #14 head. I suspect either a cracked head or blown gasket. Is there any reason to pull the pre-chambers? Will anything be revealed by doing so? And if so, is it wise to pull them while the head is still attached to the block?

It has been consuming coolant steadily over the last year, I would fill the resevoir about every 500 miles. The top radiator hose always pressurized after the engine cooled the next morning. Finally one day after a long drive, when I went to restart the engine it would not turn over due to hydro lock.

there is nothing to gain without a boroscope.

Its actually a bad idea. If you pull the prechambers, then pull the head, you may have less of a chance of noticing the cracks.

Not to mention the potential for stripping the threads out of the head for the retaining nuts and the likelihood that you will have sealing problems afterwards.

Pull the head and be prepared to replace the headgasket. As mentioned, its likely you need a new head, but not certain.

Dudernio · #5 03-15-2014, 10:52 PM

finally got around to this and only one of the pre chambers has a leak between the collar ring and the head itself. installed the proper sealing rings, cleaned the mating surfaces on the lip of the pre chamber and the seat in the head. torqued to 180 nm and it still leaks. any suggestions? will thread sealant on the screw collar be of any help?

Diesel911 · #6 03-15-2014, 11:22 PM

Quote:

Originally Posted by Dudernio

finally got around to this and only one of the pre chambers has a leak between the collar ring and the head itself. installed the proper sealing rings, cleaned the mating surfaces on the lip of the pre chamber and the seat in the head. torqued to 180 nm and it still leaks. any suggestions? will thread sealant on the screw collar be of any help?

I don't know why but the Engines with the Aluminun Cylinder Heads have the leaking Prechamber issue sometimes but I suspect that they warp.

There is an expensive Cutter and a Measuring Proceedure to follow to re-cut the seating area of the Prechamber and to pic the proper sized Seal Ring after the surface is cut.
There is info inthe DIY section.
See the attached PDF.

Dudernio · #7 03-16-2014, 12:00 AM

thanks for the above info. Also apparently when going from a #14 head to the #22, and using the old pre chambers, some modification is required to either the head or the pre chamber, looks like a 45 degree chamfer on the large diameter part of the P.C. or a corresponding milling in the head. Also, what is the correct torque on the collar nut, the FSM says 90-110 NM but I have heard it suggested to go to 180 Nm? I first went to 110 nm and it leaked, went to 180 nm and it still leaked.

Diesel911 · #8 03-16-2014, 01:08 PM

Quote:

Originally Posted by Dudernio

thanks for the above info. Also apparently when going from a #14 head to the #22, and using the old pre chambers, some modification is required to either the head or the pre chamber, looks like a 45 degree chamfer on the large diameter part of the P.C. or a corresponding milling in the head. Also, what is the correct torque on the collar nut, the FSM says 90-110 NM but I have heard it suggested to go to 180 Nm? I first went to 110 nm and it leaked, went to 180 nm and it still leaked.

I have no idea about the Torqe as I have never read the manual on that.

We have quite a few Members who have done work on these Cylinder heads. They are the ones that should be commenting on your problem