The ridge is simply an area of the liner that isn't worn. Since the rings and piston skirt don't press against it, it doesn't wear away. Carbon makes it a bit taller.

A word of caution on ridge reamers is necessary. If not used properly, they can do more harm than good. Be sure you know how to properly use the reamer and don't cut any more than is required if you're going to reuse the liner. Not cutting a large ridge will damage the piston and break the rings when the piston is pushed out of the bore. Cutting the ridge too deep or too far down into the bore will cause other problems.

Sounds like you got a cheap, assembly-line type shop. No place I've ever hired to do work works like that - it's just poor practice. Sorry you got an iffy facility. Our local machine shop here in town is about the umteenth shop I've used that requires pistons in hand before putting the block on the boring machine.

Now, can you get away with boring to a fixed size? Maybe. Depends on how consistently sized the replacement pistons are. Me and a bunch of shops that I've used say you can't rely on that. I've also heard of folks shoving new piston/ring assemblies in without checking end gaps. As a teenager (I didn't know anything back then) I seized my first rebuild by doing that - you can bet I check them now! Same deal - bad practice, and any shop I'll hire knows better.

Dan

Most ridge reamers that you'll see (at least here in the 'States) have a single blade and they LOVE to chatter. As long as you don't cut too deeply that's not TOO bad but careful use can keep that to a minimum. I find that taking many light cuts limits the chatter. Something to watch for.

Sometimes there appears to be a ridge but really it's just a carbon build-up. The reamer will EASILY remove that so watch and see if your ridge goes away w/o any actual metal removal - often it will.

Dan

Yeah, they can leave some pretty crude cuts behind. That's why I don't like them but recognize that sometimes they're necessary to get the piston out without damage. I wouldn't use one unless I was sure it was needed. Good tip about making several small cuts.

Measuring pistons and sizing bores is standard procedure for any shop I've dealt with. Many piston sets are matched for size so you don't have to bore the engine to various sizes just to the pistons in the box.

At the factory, using select fit pistons goes back to at least the 60's. I've seen pictures of Chrysler engines being built and the blocks has various letters painted on the sides to signify the bore size. These letters corresponded to pistons of various sizes.

I've even seen letters stamped on oil pan rails / edge of block decks as well.

As for any American car repair manual stating that select fit pistons are to be used, generally they specify a range and leave it at that. Newer tight clearance engines might specify but I'm not digging through a bunch of manuals to find out.

I could not tear a motor down that far (bearings, valve job, seals) and not resleeve and install new rings. Seems silly to not replace it all due to previous neglect and mileage.

BUT

Doing all that adds considerable expense to the operation.

I've also found it helpful to push DOWN as hard as I can as I turn it. It's kind of awkward but do-able and that, too, helps keep chatter to a minimum. The ridge reamer tends to ride up in the bore and off the stops built into the tool so it has more room to vibrate and less tendency to muffle it's vibrations. Worth a try - it works for me.

Dan

And that's the point in freshening up an engine rather than a total rebuild.

Rings, bearings and a valve grind do wonders in turning back the mileage clock. One could buy a used but mostly unknown used engine or take a slightly worn engine and freshen it up with parts and minimal machine work.

I pick the freshened engine. In fact, many times when install a used engine it gets bearings and sometimes a timing chain.

Will the motor be as new? No. Will it be a known quantity when finished? Yes.

Also, once the engine freshen up is complete, the clearances will be X. If someone has a running engine with miles on it, what if it has the same clearances as the newly freshened engine? Would they take the running engine apart because it is out of spec or continue to drive?

A t handle works wonders here. A ratchet puts a bending motion on the tool where a t handle is pure torque. ( And you can push down at the same time. )

Also, don't crank on the adjuster screw, there is a spring under the cutter. Don't compress it to bottom otherwise you are forcing the cutter to take too big of a bite.

Agreed on all points.

What do sleeves run for the 617 at this point in time? $100/ea?

Well, that is sort of the philosophy I am evolving into here - I don't think the engine really needs a bottom end rebuild, but since I have the motor out of the car and have all the precision measuring tools I might as well check out the internal condition.

Since the pistons will be coming out to check the condition of the ring lands, I'll definitely re-hone and install new rings. BTW, this link at the VW TDI forums talking about the Goetze rings sold here and why you change them every time the piston comes out of the cylinder was pretty interesting

https://forums.tdiclub.com/showthread.php?t=349300

Whether or not I re-sleeve will depend on whether the cylinders are all within the factory wear limits after the hone - initial measurements indicate they ought to be. I reckon that if MB took the trouble to specify the service limits, they must mean something.

I totally respect the "do it 100% or don't do it at all" philosophy, but this is being built up as a weekend warrior 'round-town kid hauler and not a full-on restoration. It is also project car #3, and if I followed that philosophy with all of them, I'd have to sell a couple of those kids to science ...

We need to make a distinction between a reasonably in spec engine that had pistons removed and a worn out engine that had the pistons removed.

If the engine is otherwise in good condition but had a piston removed ( say to have the rod reconditioned due to a bearing failure ) the rings can go back in.

If the engine is worn out, replace the rings and inspect the ring lands.

Piston rings spin as the piston goes up and down so gap location is constantly changing. Even with this occurring, I put some scratch marks on the ring land sides to show where the gap is.

Those that rigidly adhere to the "do it 100% or don't do it at all" philosophy don't fully understand how an engine works nor do they understand what really matters.

I changed the piston on an engine and used the old rings (only 90,000 miles on the OM617), and it had a terrible vibration afterward. I was told that I should have replaced the rings and honed the cylinder. The engine came apart again, and I did just that. It runs smooth as silk now. That being said, I have personal experience with using the old rings, and I will say it is not worth the cost of a set of rings, a head gasket, and the labor to find out that using the old rings was a bad idea. http://www.peachparts.com/shopforum/diesel-discussion/369253-om617-n-main-bearing-problem-im-baffled.html

x2.

I am a pragmatic guy not a purist. Engine is not rocket science, just a mechanical device. You cannot do it 100%, well you can - with a NEW engine.

Re comments on circulating oil pre-firing, I rigged a simple system from a small 1 qt garden sprayer w/ hand pump, to force oil in thru the sender hole. Seems simpler than a pressure-cooker setup. I have used on U.S. gas engines (1/8" NPT sender). If I used on my OM617, I have a spare fitting w/ nylon tube for the oil pressure gage I could use. Otherwise, you could connect a rubber hose to the dash side of the tube. I use a spring clamp to hold the sprayer's trigger in. Pump to 20 psig, come back in an hour and the qt is gone, which should be enough to pre-charge all the bearings and passages, or run another qt thru.