Cylinder Wall Quandry

I think I already know the answer to this, but before I go spending a bunch of money (or having a viking funeral) I figured I should ask the most knowledgeable people I know.

To recap the saga, this is on my Mercedes OM642 engine.  The #2 rod bearing got totally destroyed and as a result, the piston banged around a little bit.  As I was getting the block ready to drop the pistons back in, a vertical scratch in the #2 hole became obvious.  I mean, the middle cylinder on the right bank.

After a quick hone with a Flex Hone, there's no more ridge, but the scratch can be felt.  It looks basically like this:

The Right Thing to do would be to bore the engine .5mm over and get 6 new pistons and their respective rings.  I don't know what the machine shop cost would be, but the pistons would be $1,140 for the set, give or take.

Another option would be to try to find a used block.  I have to make some calls, but so far all I've found was one for about $1,200.

The third option would be to run it as is. 

So, I pose the question to GRM:  Do I need to correct that scratch or will I just burn a little more oil and make a little less compression and never really notice?  I already have the crank fixed, the oversized main and rod bearings, and my plan was to install all that, slap the old pistons back in, re-use the old oil pump and timing setup (the new extended warranty terms as part of the settlement with Merc cover the timing chain), put the heads back on, and run it.  The chassis has 125k miles on it and I never did make a decision as to if I would get it running, have the settlement work done, take my check from Merc and sell it or just keep it.

Are you seeking perfection?  I'd run it, myself.  It's far enough down the bore that there won't be max cylinder pressure by the time the rings get to it, so it will work adequately.

I would be far more concerned with using the piston.  No evidence of it having hit the cylinder head, pinching ring lands?

All the rings move freely and the piston looks like this:

In reply to Streetwiseguy :

It's not perfect but then what is in that car?   There is a point to stop chasing perfection and if you look behind you it's back there someplace. 
     But maybe you're the type of person that will bother you as long as you own it? 
 In that case go for perfection.  I've put an odd size piston in on a tired motor and the darn thing never gave me a lick of a problem as long as I owned it. 

In reply to frenchyd :

I mean...  boring out the one cylinder, drilling out the underside of the oversize piston to fix the weight, and running slightly mismatched bores isn't really off the table either.

Perfection isn't going to happen here.  Perhaps you missed the part where this is in a Mercedes OM642 engine!  (kidding!)  It seems like in almost every situation there's a lot of room between the manufacturer spec and what will actually work in the Real World.  All I'm trying to avoid is putting myself in a situation where I'm likely to go through all this work just to find out that it all has to come apart again because I thought I could get away with something.  Or at least do reasonable things to reduce that chance....

I've seen and have done myself throw many 2 strokes back together with much worse wear than that. No noticeable difference in power or oil use and lasted the normal expected life before the next rebuild.

My formerly professional engine builder opinion: Piston looks just fine and the bore too. Run IT!

You should care about that as much as the junkyard LS guys care about the cam bearings when they are stabbing a cam in a stock high mileage motor.

The flex hone probably made "more" problems than the scratch will.  I'd say hit the cylinder with some 600 grit sandpaper on a regular hone to smooth out the finish, and run it.  Or wipe it out with ATF on a rag and run it.

it was running fine before, aside from the hellacious noises, right?  Not blowing smoke or anything?

I'd run it, especially considering where the scratch is. 

I'd run it.  You took it apart for a noise not lack of power.  I can't see that having any impact on your car.

Yep, that motor came apart because of the noise - even when it was ticking like a fiend there was no smoke blowing out the exhaust and it was making power just fine.

Looks like it's unanimous, then and I need to get back to work putting that thing back together!  Thanks, gang!