Here's the photo showing both... #22 on the left, #14 on the right, but #'s 15, 17, 18, and 20 all have the same oil passage as the 14. Note that on the 14, the oil passage is open to the head surface, about 4-5 inches long. A fairly common failure is blowout of the head gasket on either side of this passage. The new #22 design closes most of the passage to the surface, just having an inlet & outlet on each end. It's not something you could modify on an older casting. It's probably not a huge deal, but if you can't find a really good price on a used #17, I'd go with a new #22. This wouldn't keep me from using a straight, crack-free #17 if I could find one for ~$500!!

Got it.. It almost looks like you could weld and surface a good >=17 head to achieve the same result.

so just to confirm and make sure I'm dead on here.

a 3.5 head (>= 17 casting) from a 90-95 6cyl 300 series car (if complete with injectors etc)
is a direct bolt on.

otherwise you buy new and transfer parts... (#22 casting)

Is this accurate?

Basically, yes, that is accurate. If you get the complete 90-95 3.5L head with injectors, etc... your old metal injection lines will need to be CAREFULLY bent to fit the angled/inclined injectors. But otherwise, yup, you're all set. Note that the lock rings for the old/vertical prechambers, and new/angled prechambers, are totally different. The old setup uses a "pin wrench", the new setup uses a splined tool:

New style:
http://www.w124performance.com/images/tools/prechamber_late1.jpg

Old style:
http://www.w124performance.com/images/tools/prechamber/BT_lock_ring_tool_std.jpg

Excellent, Thanks kindly!

now, more questions..

How frequent is the blown headgasket issue? does this result in coolant in the oil? pressure in the crankcase? Could this just be the result of an improper torque sequence?

The blown headgasket issue is much less common. Generally it seems to be a problem between the timing chain cavity and the #1 cylinder, in which case oil consumption will skyrocket, and it may blow blue smoke. The head gasket can fail in other areas, causing oil in the coolant, or if the engine is overheated and the head warps, you could get oil in the coolant. Also, there is a note in the factory WIS that some heads could have excessive porosity in the forward oil galley, causing oil in the coolant, despite passing the pressure test described in the FSM. That's probably rare though. I doubt improper torque sequence is related to any of the gasket issues, the sequence is spelled out in the manual pretty clearly, and not many newbies attempt this job...!

Further to this excellent thread.

I'm replacing a cracked #14 head with a good #17 head on my 87 300SDL. My question is about using the prechambers from my old #14 in the new #17. The machinist who's helping is experienced with Mercedes heads, I was sent to him by one of the best indie Mercedes mechanics in LA. He's never swapped old straight prechambers into newer >#17 heads, and is concerned about the size and thread differential between the older slotted-collars and the new spline-style collars which hold the prechambers in place. (He doesn't have the old head at the moment, is just pressure-testing the #17 head.) He says it looks to him like the spline collar is much longer than the slotted ones, and doesn't know if the old #14 pre-chambers can be sealed into the new #17 heads by using the old slotted collars. This is only a question about the sealing collar size and thread, since the earlier posts seem to show that the pre-chamber interchange itself if not a problem. (Trying to keep my old injectors just rebuilt with Monarks)

Thanks!

You can use the old prechambers in the newer head, but you need to also use the old lock rings, and old injectors. Otherwise it should bolt together.

There's a sliiiiight concern about if the old prechambers will fully seat in the bore, if not, you can either machine the bore in the head, or the prechambers. If the head will be at the machine shop, they can check to make sure the prechambers are seating properly. Worst case you'll learn the hard way like I did, after I had the engine back together and I had major compression leakage. At that point you can pull the prechambers, machine them, and re-install. I had to do that when I put a new #22 head on circa 2002. Pics are on my website here.

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Dave
Boise, ID
Check out my website photos, documents, and movies!

Make sure you have the correct length glow plugs for whatever combination results.

Jeremy

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"Buster" in the '95

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