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Old 09-10-2010, 12:06 PM
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Precombustion Chamber Seals

I pulled the head on my '92 300D to replace the head gasket. While it was off I took it to the machine shop to have it checked over. Turns out the head needed to be resurfaced, so they pulled the precombustion chambers. They are now putting it back together and asked me to bring in the precombustion chamber seals in my head gasket kit. The problem is that there do not appear to be any precombustion chamber seals in the gasket set. There are injector heat shields but no other seals that I can identify as PC seals. It is the standard Victor Reinz gasket set. I have also searched for the PC seals and no luck so far. Any help would be much appreciated.

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Old 09-10-2010, 12:11 PM
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these heads do not use PC seals.

an experienced shop should know some clever trick to seal them.

a machinist I use said that 'some' shops use the seals from earlier style engines. But I would not be surprised to find that they use a high temp epoxy / filler for stubborn leaks.

sounds like your shop has not worked on these heads as much as you would have hoped for.
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Old 09-10-2010, 12:15 PM
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Thanks JT. That is what I was thinking, at least about the lack of a seal. Now I have to figure out if I trust them to put it back together.
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Old 09-10-2010, 12:21 PM
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If you do some searching on this site, and others, you'll find this does happen more often than any of us would like to imagine.

it really is not a great compression loss, but a loss nonetheless.


additionally, in the service manual, there is a section on reaming / resurfacing the bores in the head for the prechambers.
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Old 09-10-2010, 12:44 PM
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Quote:
Originally Posted by Biosudds View Post
I pulled the head on my '92 300D to replace the head gasket. While it was off I took it to the machine shop to have it checked over. Turns out the head needed to be resurfaced, so they pulled the precombustion chambers. They are now putting it back together and asked me to bring in the precombustion chamber seals in my head gasket kit. The problem is that there do not appear to be any precombustion chamber seals in the gasket set. There are injector heat shields but no other seals that I can identify as PC seals. It is the standard Victor Reinz gasket set. I have also searched for the PC seals and no luck so far. Any help would be much appreciated.
There are not "seals" as such for the prechambers after machining a cylinder head, but there may be an issue and there is a factory fix.

After a cylinder head is resufaced removing material reduces the "height" of head and as a result the pechambers can protrude into the combustion chamber beyond tolerance interfering with the piston! The protrusion tolerance of the prechamber into the combustion chamber is 7.6 - 8.1 mm, only half a mm!

The factory fix is to determine the measurment of the adjustment needed to bring things within specs, then appropriate "spacers" are obtained from MB, then the prechamber's seat is cut a specific depth. That way the combination of cut depth and spacer thickness are used to adjust the protrusion depth of the prechamber. The spacers are steel and available in fixed thickness amd there is a tool specifically designed to cut the prechamber seat depth, although a good shop can probably work up a standard tool to the proper profile and cut the prechamber seats on a mill after carefully measuring and calculating the dimensions needed.

The factory operation is detailed in the OM 602/3 FSM 01-410, the Spacer Rings are 601 017 04 60 - 0.3 mm, 601 017 02 60 - 0.6 mm, 601 017 03 60 - 1.0 mm and the factory tool is 601 589 00 66 00 I know Samstag has it for about $500!

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