Hi,

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!

For engines in general as I don't know the specifics of your engine:

In the old days, mass production left parts slightly varying in size but still called Standard size. Blocks were bored / honed then measured. Pistons were made and measured. Small bores got small pistons and large large, this is select fitting. Some engines had paint on the outside of block / stampings on the deck for select bore sizes.

Sometimes the factory will build an engine with non standard sizes as a repair measure but this is pretty rare.

Pistons are generally kept in sets for weight even if size varies slightly. Piston rings are rarely available in select fit. ( Some popular race engines have 0.005" oversize rings to allow for loose bores / tightening up ring gaps.)

Modern manufacturing has largely eliminated the process though some engines still use select fit crankshaft bearings.

For a field rebuild, select fit parts are usually not used, just be sure to measure the parts. Rebuild tolerances will be wider than a factory build.

Thanks for the fast response, here is the section of the service manual I was referring to.

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

I would assume that as long as I put the two pistons with the '1' designation in their respective bores, I would be ok just to order 5 sets of normal rings and be done?

You might want to ask a moderator to move this to diesel discussion. There's a lot of diesel specific knowledge there and many of the dieselheads never look in tech help.

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83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
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Yes, put pistons back where they cam from as long as the piston to wall clearance isn't too large. A regular "standard" set of rings will be fine. The difference between a 0 and 1 piston is 0.010 MM ( 0.00039 " ) Ish.

Piston to cylinder clearance for a new engine is 0.043 - 0.063 MM (.0016" - .0024" ) with a wear limit of .12 MM ( .0047" ) As you can see the wear limit envelops the 0 , 1 and 2 piston sizes.

New engines are built tight for low noise / life. Used part rebuilds ( freshen up repairs ) can be looser due to worn parts. The wear limit can be pushed on pistons a bit as long as you accept that the motor won't last as long.

I've done a fair amount of "junkyard rebuilds" over the years, sometimes the car body does not warrant a 200,000 mile motor , good used engines can't be found and a 50,000 + mile suits the bill just fine.