Prechamber Sealing Rings? - PeachParts Mercedes-Benz Forum

retmil46 · #1 11-21-2011, 08:32 PM

Looks like I have leakage around the prechambers on 3 cylinders (87 300D OM 603). I poured a small amount of clean oil around the base of each injector and fired up the engine - on 3 cylinders, I had air/combustion gases bubbling up around the outside of the threaded ring holding in the prechambers - quite noticeable at cold idle, decreases but still obvious when hot.

Nothing around the base of the injectors themselves. 212K miles on the engine, and it shows evidence that the injectors have been reworked and/or replaced with rebuilts sometime in the past. So I'm surmising that the prechambers got loosened up as a result of the injector work.

To make a complete job of it, I'm planning on pulling and cleaning all the prechambers, sending the injectors off to be tested, and doing the standard routine on the delivery valves.

Problem is, I haven't seen where anyone sells new sealing rings for the prechambers. Does anyone have a lead on where I could get new ones, a part number, or are the old ones reuseable after a good cleaning?

GregMN · #2 11-21-2011, 10:45 PM

I found them at the dealer. Stupidly expensive for what they are. But, they sealed the chamber to the head and stopped the air leak.

Brian Carlton · #3 11-21-2011, 10:53 PM

Does anyone have a thought as to why it wouldn't be possible to simply clean up the faces of the rings with a fine stone or some fine emery paper?

Do they go badly out of flat so that any reconditioning is impossible?

libbybapa · #4 11-21-2011, 11:45 PM

I have noticed that any time diesel is spilled around the injector threads it will bubble up as it boils off. That is not an indication of leakage, it's just how it evaporates. I imagine oil would do the same thing. I would suspect leakage on the cylinders that *didn't* do that as the oil likely leaked into them instead of boiling off.

fochs · #5 11-22-2011, 03:28 AM

Carquest auto parts should have them. They had the ones for my 83 240d and seem to be able to get a lot of oem parts . Looks to be one in your area - knob creek rd.

retmil46 · #6 11-22-2011, 06:09 PM

Quote:

Originally Posted by libbybapa

I have noticed that any time diesel is spilled around the injector threads it will bubble up as it boils off. That is not an indication of leakage, it's just how it evaporates. I imagine oil would do the same thing. I would suspect leakage on the cylinders that *didn't* do that as the oil likely leaked into them instead of boiling off.

It wasn't diesel fuel - clean 15W40 engine oil - and I don't think there was initially any boiling involved - engine was stone cold after sitting for four days, but as soon as I fired it up there was the bubbling around 3 of the threaded prechamber rings.

retmil46 · #7 11-22-2011, 06:15 PM

Quote:

Originally Posted by fochs

Carquest auto parts should have them. They had the ones for my 83 240d and seem to be able to get a lot of oem parts . Looks to be one in your area - knob creek rd.

Yep, I know where that one is, over in an industrial park where many of the Nascar teams have their shops located. Been there many a time, as they used to be the only ones in this area that carried Zerex G-05 antifreeze. I'll give them a try on Friday if they're open.

fochs · #8 11-22-2011, 07:40 PM

Viva la NASCAR!

retmil46 · #9 11-23-2011, 10:02 PM

Well, I checked the W124 Service Library CD, and discovered why no one carries prechamber sealing rings for a 603.

602 and 603 don't use sealing rings - metal to metal fit between the prechamber and cylinder head - IOW, they don't exist.

To repair the sealing surface inside the cylinder head if it's damaged or leaking, you have to use a countersinking tool and actually grind metal off the sealing surface.

By measuring before and after, you then add one of three different thickness spacer rings - 0.3mm, 0.6 mm, or 1 mm - to keep the depth of the prechamber correct.

You can do this once with the cylinder head installed. If necessary to repeat the process down the road, it says that on any subsequent attempts you have to remove the cylinder head to get an accurate measure of the depth.

If this has been done to any of your prechambers by an MB mechanic, they're supposed to stamp a mark in the cylinder head above each prechamber that required use of the countersinking tool and addition of spacer rings.

IOW, it sounds like if you have badly leaking prechambers on a 602 or 603, such that it's fairly certain you'll need to repair the sealing surfaces, this isn't really a DIY job like it is on the older engines where you could just plop in a new sealing ring, and you'd be better off letting a competent MB mechanic handle it.

At that, sounds as if you might as well buy new prechambers too - with a metal to metal seal, if the surface inside the cylinder head is damaged from leakage, odds are the sealing surface on the prechamber is trashed as well.

Diesel911 · #10 11-24-2011, 12:04 AM

Quote:

Originally Posted by retmil46

Well, I checked the W124 Service Library CD, and discovered why no one carries prechamber sealing rings for a 603.

602 and 603 don't use sealing rings - metal to metal fit between the prechamber and cylinder head - IOW, they don't exist.

To repair the sealing surface inside the cylinder head if it's damaged or leaking, you have to use a countersinking tool and actually grind metal off the sealing surface.

By measuring before and after, you then add one of three different thickness spacer rings - 0.3mm, 0.6 mm, or 1 mm - to keep the depth of the prechamber correct.

You can do this once with the cylinder head installed. If necessary to repeat the process down the road, it says that on any subsequent attempts you have to remove the cylinder head to get an accurate measure of the depth.

If this has been done to any of your prechambers by an MB mechanic, they're supposed to stamp a mark in the cylinder head above each prechamber that required use of the countersinking tool and addition of spacer rings.

IOW, it sounds like if you have badly leaking prechambers on a 602 or 603, such that it's fairly certain you'll need to repair the sealing surfaces, this isn't really a DIY job like it is on the older engines where you could just plop in a new sealing ring, and you'd be better off letting a competent MB mechanic handle it.

At that, sounds as if you might as well buy new prechambers too - with a metal to metal seal, if the surface inside the cylinder head is damaged from leakage, odds are the sealing surface on the prechamber is trashed as well.

You will not need new prechambers unless there is some sort of obvious cutting done by the combustion on the prechamber. And, the Prechamber is made of material that is supposed to withstand normal combustion so they are most likely OK.

Aluminum on the other hand shifts around a lot due to heat. No telling what type of stress the whole Cylinder Head undegoes.

It might be that you simply need to retighten the Prechamber Retaining Rings/Collars. (Or maybe you could pull out the Chamber and clean things up and retighten and see if it seals.)

I believe in one of the other threads on the subject someone suggested a thin Copper Washer.

There are also high temp sealants.

If you Pull out the Precombustion Chambers be sure the Piston is up near top dead center as a lot of crap gets peeld off the Prechamber as you pull it out.
If the crap is laying on top of the Piston where you can see it;it is easier to get out.

I put a Shop Vac over the Injector Hole and it sucked most of the loose stuff out.

retmil46 · #11 11-24-2011, 08:59 AM

Quote:

Originally Posted by Diesel911

You will not need new prechambers unless there is some sort of obvious cutting done by the combustion on the prechamber. And, the Prechamber is made of material that is supposed to withstand normal combustion so they are most likely OK.

Aluminum on the other hand shifts around a lot due to heat. No telling what type of stress the whole Cylinder Head undegoes.

It might be that you simply need to retighten the Prechamber Retaining Rings/Collars. (Or maybe you could pull out the Chamber and clean things up and retighten and see if it seals.)

I believe in one of the other threads on the subject someone suggested a thin Copper Washer.

There are also high temp sealants.

If you Pull out the Precombustion Chambers be sure the Piston is up near top dead center as a lot of crap gets peeld off the Prechamber as you pull it out.
If the crap is laying on top of the Piston where you can see it;it is easier to get out.

I put a Shop Vac over the Injector Hole and it sucked most of the loose stuff out.

I'm hoping that a good cleaning and retightening will be all that's needed - but given the amount of neglect and sheer stupidity on the part of the PO's I've found so far on this vehicle - no telling how long those prechambers have been leaking by - I wouldn't be surprised if I have to do some sealing surface repair on the cylinder head.

If the prechambers themselves are made out of harder material than the aluminum head, that presents another option - taking one of the old prechambers that's still in good shape, grinding off the locating lug so that it can be rotated/spun inside the well, and using it as a makeshift lapping tool along with some fine grade lapping compund or jewelers rouge to polish the sealing surface on the cylinder head.

Given my several years experience in the Navy doing nuclear grade valve repair, particularly lapping in the sealing surfaces on same, I'd be far more comfortable with this approach, than with using what amounts to a reamer and shaving off metal.

If need be, I'd prefer to repair the sealing surface, than resort to using a band-aid such as a copper washer or sealant - nothing against those that use this approach, just not what I'd prefer to do.

funola · #12 11-24-2011, 09:23 AM

Quote:

Originally Posted by retmil46

...................................................................................................G iven my several years experience in the Navy doing nuclear grade valve repair, particularly lapping in the sealing surfaces on same, I'd be far more comfortable with this approach, than with using what amounts to a reamer and shaving off metal.

If need be, I'd prefer to repair the sealing surface, than resort to using a band-aid such as a copper washer or sealant - nothing against those that use this approach, just not what I'd prefer to do.

What is nuclear grade valve lapping?

To check if there is a leak from the pre-chambers, shaving cream works better compared to a liquid such as soapy water or oil.

Diesel911 · #13 11-24-2011, 10:48 AM

Quote:

Originally Posted by retmil46

I'm hoping that a good cleaning and retightening will be all that's needed - but given the amount of neglect and sheer stupidity on the part of the PO's I've found so far on this vehicle - no telling how long those prechambers have been leaking by - I wouldn't be surprised if I have to do some sealing surface repair on the cylinder head.

If the prechambers themselves are made out of harder material than the aluminum head, that presents another option - taking one of the old prechambers that's still in good shape, grinding off the locating lug so that it can be rotated/spun inside the well, and using it as a makeshift lapping tool along with some fine grade lapping compund or jewelers rouge to polish the sealing surface on the cylinder head.

Given my several years experience in the Navy doing nuclear grade valve repair, particularly lapping in the sealing surfaces on same, I'd be far more comfortable with this approach, than with using what amounts to a reamer and shaving off metal.

If need be, I'd prefer to repair the sealing surface, than resort to using a band-aid such as a copper washer or sealant - nothing against those that use this approach, just not what I'd prefer to do.

Correction below
Go for it!

retmil46 · #14 11-25-2011, 04:27 PM

Found one of the old threads on homemade and aftermarket prechamber tools, in which gsxr had chimed in, and made the discovery that the injectors are actually threaded into the prechamber locking ring. A few things fell into place after that.

It raised the real possibility that the leakage I'm seeing isn't past the prechambers at all, but that one of the PO's mucked up the injector heat shields and that's where I'm actually seeing leakage from.

You'd have had to see the overall condition of the IP and injectors when I first bought the beast, to realize why I'm counting this as a stronger possibility than the prechambers themselves now - the locking collars for the delivery valves on top of the IP were stacked up 3 high and somewhat locked down at crazy angles, instead of the proper alternating pattern - the injector return lines were so rotten that after 2 days there was fuel running down the side of the engine and pooled in 4 of the 6 injector wells - with that type of nonsense going on, I can imagine what type of job they did pulling and reinstalling the injectors - and wouldn't be surprised in the least to find most if not all of the heat shields installed up side down - that's if they even bothered to change them out.

Already had all the injector tools and 4 sets of heat shields. Today I ordered one of the locking ring pin wrenches (early 603, car built in July 86) from Fastlane, and will be looking to acquire some type of prechamber puller as well - might as well make a complete job of it, no telling what type of nonsense I'll find once I get the injectors pulled.

Diesel911 · #15 11-25-2011, 11:07 PM

Quote:

Originally Posted by retmil46

Found one of the old threads on homemade and aftermarket prechamber tools, in which gsxr had chimed in, and made the discovery that the injectors are actually threaded into the prechamber locking ring. A few things fell into place after that.

It raised the real possibility that the leakage I'm seeing isn't past the prechambers at all, but that one of the PO's mucked up the injector heat shields and that's where I'm actually seeing leakage from.

You'd have had to see the overall condition of the IP and injectors when I first bought the beast, to realize why I'm counting this as a stronger possibility than the prechambers themselves now - the locking collars for the delivery valves on top of the IP were stacked up 3 high and somewhat locked down at crazy angles, instead of the proper alternating pattern - the injector return lines were so rotten that after 2 days there was fuel running down the side of the engine and pooled in 4 of the 6 injector wells - with that type of nonsense going on, I can imagine what type of job they did pulling and reinstalling the injectors - and wouldn't be surprised in the least to find most if not all of the heat shields installed up side down - that's if they even bothered to change them out.

Already had all the injector tools and 4 sets of heat shields. Today I ordered one of the locking ring pin wrenches (early 603, car built in July 86) from Fastlane, and will be looking to acquire some type of prechamber puller as well - might as well make a complete job of it, no telling what type of nonsense I'll find once I get the injectors pulled.

With the Stock Prechamber Puller you need to use a Slide Hammer.

This means you need to find out ahead of time what the Prechamber Puller where the Slide Hammer attaches is threaded for.