I am rebuilding my OM616 engine for my 1975 W115 240D. I picked up a re-conditioned block and head from an abandoned project. The block was re-sleeved and the head came from MBZ parts. (inspected and tested) The block came with new pistons. See picture.

My question. Do I have to correct pre-chambers (see picture) that can be installed with this style of piston?

The information on line is very confusing as is the workshop manual.

Any help or advise is very much appreciated.

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i believe if you mill the head you need to do the chamber to match.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

The head has not been machined, just inspected. There are two types of Chambers available. The one in the picture and also a version that has a rounded tip. Not sure which one I need to use or if it even matters.

So going through the manual,

-the original type of pistons in w115 240d would look like :

https://www.peachparts.com/shopforum/attachments/diesel-discussion/94422d1312305275-616-rebuild-options-img_0507.jpg

They are used with flat tip prechambers, the one that you showed in your photo.

Later MB introduce the star-shaped combustion chamber pistons with two different type of recesses - flat and rounded(for the so called "uprated engines" in the manual) :


Flat tip PC's are OK with :
-pistons with round shaped comb.chamber (as originally)
-and star shaped Cchambers having the flat recess (type C)

..........

Round tip PC are to be used with star shaped chamber with rounded recess (type D) .
They should not be used with star shaped , flat recess chambers (Type C)
...or with the round combustion chamber cavities (like the older type om615/616). These are only in om615/616 context !



However, the way I read the manual ,the flat recessed star chambers (Type C) are applicable only to om615's pistons .

So your PC's seem to be unsuitable for the NE pistons that came with the block (because they probably have the rounded recess-and that is IF the star-shaped flat recess of type C ever existed in 616-617 pistons ).

I tried to look closely at the your photos,also checked some other,like this genlteman here:

https://www.flickr.com/photos/govert1970/albums/72157625987974204/

Note that he upgraded to the round tip prechambers. The new pistons look to have a rounded "star" recess(type D)...but light and photo angle play tricks...

Also , the NPR catalog lists only 1 type of om 616-617 pistons, page 202 :
https://www.npr-europe.com/wp-content/uploads/2024/08/P7-Katalog.pdf

They probably went with the most "popular" option, the "rounded" recess star (for later type, rounded tip PC's)...


Also, some pics from YT of a guy restoring a w115 om615 using "star"and flat recess pistons .



Note that he is keeping the original flat tip PC's .



Check first the type of recesses yours have...but judging by the manuf.catalog they're probably rounded.


A thread with part #'s :

http://www.peachparts.com/shopforum/mercedes-parts-reference-library/315201-om616-916-extreme-rebuild-parts-list.html

http://www.peachparts.com/shopforum/diesel-discussion/170391-different-type-prechambers.html

6160100152 - om616 prechamber , round tip, 616/01 marked .

Well...that's what I could gather . Hope that someone who's been through it would chime in.
Note the star shape in the Service manual and the currently offered pistons differ ...hm...

Attached Files

	615-6-7 pistons1.pdf (683.0 KB, 51 views)
	615-6-7 pc 1-5.pdf (427.1 KB, 44 views)

Thank you vox-incognita. I see in the pictures from Flickr that the pistons installed are identical to what I have and that he did indeed change out the flat tipped PC's for the rounded style. This is what I suspected I would have to do. Now I need to see if I can find any used PC's in North America. Really appreciate your help and information.