Replace Piston Rings While Motor is Disassembled? - Page 3 - PeachParts Mercedes-Benz Forum

dieseldiehard · #1 03-01-2016, 11:32 PM

I remember reading the 123 Factory manual on brakes, was shocked to learn the factory recommends using a special brake pad to recondition rotor surfaces, in the boondocks or third world countries I suppose. They make (made?) them out of some sort of highly abrasive material (sandpaper grit?).
Clever, huh?

leathermang · #2 03-01-2016, 11:38 PM

LOL, Like I said... OCD in the best way....
totally different rules if you want to do it right...

BillGrissom · #3 03-03-2016, 12:22 PM

A slight data point. My 1985's engine had ~250 psig in all cylinders (recall) at ~300K miles. It needed the block heater and several glows to fire on 30-40 F mornings. At 330K, the engine seized w/ much bore scars and chunks missing from several piston ring grooves. My 1984's engine has one cyl ~340 psig (recall) and the others ~400 psig at unknown mileage (cluster from PickNPull). It has no block heater and starts on the coldest days.

Typically, rings wear faster than bores since less surface area. You might get another 100K as is before cold starts get hard and more blow-by. The sleeves aren't hard to change (I did), but requires machine shop work (I haven't done yet).

leathermang · #4 03-03-2016, 02:39 PM

When you went in the 50's, 60's, or 70's and bought a remanufactured GASOLINE engine short block... which was the most economical thing to do... I promise you they were not matching up individual pistons to individual holes.... they got as close as they could on average... and had a 100k miles warranty....The block had had some standard things done to it like Vatting... which is often skipped these days... surfacing and line boring... all set up on an assembly line... they were good engines at a good price...which they could do because they were not individually matching pistons to their respective holes...

Dan Stokes · #5 03-03-2016, 03:54 PM

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

97 SL320 · #6 03-03-2016, 07:35 PM

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.

Hit Man X · #7 03-03-2016, 10:50 PM

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.

97 SL320 · #8 03-04-2016, 06:04 PM

Quote:

Originally Posted by Hit Man X

. . .

BUT

Doing all that adds considerable expense to the operation.

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?

Hit Man X · #9 03-04-2016, 08:31 PM

Agreed on all points.

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

pragmatic · #10 03-05-2016, 08:42 AM

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 ...

97 SL320 · #11 03-05-2016, 12:33 PM

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.

ROLLGUY · #12 03-05-2016, 01:09 PM

Quote:

Originally Posted by 97 SL320

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.

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. OM617 N/A main bearing problem- I'm baffled

97 SL320 · #13 03-05-2016, 05:27 PM

Quote:

Originally Posted by ROLLGUY

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.

What you state isn't entirely true according to the posts referenced in your thread. Posts 79 / 80 speak of an engine that will barely run and need half throttle to do so after the piston / old ring replacement. For a set of rings to cause this you you would have massive blow by / lube oil smoke.

Post 91 speaks of the wrong piston top profile being used and post 92 gives a link to mixing piston top profiles but does not give any hints as to compression ratio changes if parts are mixed and matched.

At 90K miles I probably would not move rings from one piston to another but the old rings sure didn't cause the starting / vibration problem you had.

ROLLGUY · #14 03-05-2016, 05:57 PM

Quote:

Originally Posted by 97 SL320

What you state isn't entirely true according to the posts referenced in your thread. Posts 79 / 80 speak of an engine that will barely run and need half throttle to do so after the piston / old ring replacement. For a set of rings to cause this you you would have massive blow by / lube oil smoke.

Post 91 speaks of the wrong piston top profile being used and post 92 gives a link to mixing piston top profiles but does not give any hints as to compression ratio changes if parts are mixed and matched.

At 90K miles I probably would not move rings from one piston to another but the old rings sure didn't cause the starting / vibration problem you had.

I don't know what to tell you, but before re-ringing and honing that bore, it vibrated so bad that it walked the engine sideways after idling for only a few seconds. I pulled the head, honed the cylinder, and put it all back together and it runs perfect. That is enough for me.

ah-kay · #15 03-05-2016, 01:47 PM

Quote:

Originally Posted by 97 SL320

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.

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.

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