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  #1  
Old 07-01-2014, 07:08 PM
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Moved: OM617 Pistons Group 0,1,2

Hi, originally posted in tech, completely missed the "diesel" section.. new to the forum. Simple question

In reference to the shop manual for my 1982 OM617, It shows pistons with "groups", labeled 0,1,2. Are these the oversize variations? 0 being standard...1..then 2.. etc? The reason why I ask, is my new to me engine (I bought in pieces has 3 pistons labeled 0 and two pistons labeled 1. Is this kosher? It was supposed to have been rebuilt, and it looks like it has (cylinder walls fresh cross hatched..etc) The engine had been run a couple times then stored for about 10 years before I bought it. Thats why I've torn it down to inspect and clean before building it back up. I was thinking about re-ringing it (flywheel wasn't indexed so I might have to pull the crank anyway) but in looking at rings I only see standard... are they going to fit my two pistons with the "1" designation? Sorry, a little bit green at this.

Thanks for any help!

http://www.furi-dorifto.com/tech/MB_w124_Manual/W126/w126CD1/program/Engine/617/03-316-1.pdf

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Old 07-01-2014, 08:01 PM
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The grouping of pistons do not mean regular oversized pistons fitted for oversized bores.

Mercedes at the factory tries to machine all the bores the same. What happens after the machining process, there are slight differences in the bore sizes. The factory would then choose a group of pistons out of three groups that matches the cylinder best.

617.95x info..
Group 0 = piston dia. 90.845-90.855 mm = cyinder dia. 90.898-90.908 mm

Group 1 = piston dia. 90.855-90.865 mm = cyinder dia. 90.908-90.918 mm

Group 2 = piston dia. 90.865-90.875 mm = cyinder dia. 90.918-90.928 mm
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  #3  
Old 07-01-2014, 08:39 PM
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Thank you! I wanted to be sure that someone didn't ovrrbore 2 cylinders and leave other two, sounds like everything is normal. I suspected that it was a non issue with the size increase between pistons, but wanted to be sure! Thanks!
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Old 07-01-2014, 11:40 PM
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Iirc, the flywheel is neutrally balanced.
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Old 07-02-2014, 12:34 PM
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sure be really nice if it was, I really don't "want" to do any more work than I have to, I've heard that some are and some aren't.. has anyone nailed down anything more definitive? Most of the topics that I've found are a couple years old now. The 240D flywheel I want to install was indexed or marked with paint but I doubt it means anything. In the book it says it was balanced as assembly but what that means I'm not sure.. I've read that IF my setup is externally balanced I SHOULD have some engravings or punch marks on the crank and flywheel?.. somebody saying that its neutral with 22,000+ post does comfort me a bit though
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Old 07-02-2014, 06:47 PM
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Be sure to link / copy paste / close your other thread.
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  #7  
Old 07-09-2014, 06:30 PM
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pistons and bore sizes

In my project, I have pistons with the following markings:

on the crown:
90.86
1

Inside:
ML3-1
and
NORAL
9111R2 X
4 .87

My machinists (one shop closed down mid-project) installed new liners
and bored them to 3.552". This translates to 90.221 which is below the smallest spec, so I probably need to send it back? I have the factory pages
with the numbers quoted above.

I need a source for oversize rings. Any suggestions?

thanks,

Stuart
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  #8  
Old 07-09-2014, 07:15 PM
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Have the pistons / bores measured to be sure. The pistons won't fit according to your #.

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