I was told by several good people that you have to resleeve a block and replace the psitons with oversize pistons once you pull the pistons because the block bores wear in an oval fashion. It makes no sense just to pop new piston rings on there. Is this true? I am rebuilding a Diesel with Mercedes shop forum help right now.

On my 240D I didnt resleeve and I used Deves rings ant a year later it blew oil like crazy. On my Volvo diesel rebuild I lost no oil.

resleeve yes new pistons not necessarily.depends on original piston condition.any good rebuilder would be able to measure and advise.dont recommend the old "berlin rebuild" that being rings only.i did this on an old volvo(vw) diesel.it worked well but the engine was noisy.

Berlin rebuild.
Who cares if'd be noisy, these cars are noisy anyway.

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DJ


84 300D Turbodiesel 190K with 4 speed manual sold in 03/2012

"was told by several good people that you have to resleeve a block and replace the pistons with oversize pistons "

The economic value to a system where you can resleeve the block is that if you have well made pistons... then you go back to original sleeve size and reuse the pistons...

This is particularly important with the Turbo Mercedes because the pistons are so expensive.

The sleeves are only about $35 dollars Each... pistons for a 5 cyl can run $1000...

So new sleeves bored to match your piston, and new rings (even special one from Deves to compensate for ring land wear ) is the sweet point for doing it right and at reasonable cost.

I thought about this before I jumped and went new pistons (stock, not oversize) and new sleeves. The sleeves need to be precision bored and honed. I pressed the sleeves out and in myself with a tool I made, and cut down the tops of the sleeves to match the block deck. If your pistons are OK, you are in luck, but mine weren't. Deves makes a special set with overwidth top rings, but my ring lands were too worn on the second groove also. The last I talked to them I suggested that they consider making a set with 2 wider ring sizes as there would be a market for it. I got my set of Mahle pistons and rings from Rusty for $675 but the prices on those have gone up a LOT since then. Carrameow, I know you can do it, but that motor is a lot of work. Good, used engines take less time.......

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

If the cylinders mic out within spec, replacing the rings would be acceptable. The likelihood of that being the case on one of these engines is probably wishful thinking.

Secondly, if cylinders do indeed need attention, you don't HAVE to replace the liners, you can bore the liners to an oversize just as you would with any engine then use oversize pistons.

The other option would be to resleeve which must be done by a machine shop. They replace the sleeves, cut the top with a boring bar and then finish to size if necessary, then reuse the original pistons. This is my least favorite approach. Although it is typically the least expensive, you are reusing the second most highly stressed part in the engine, the piston.

My $0.02,

" reusing the second most highly stressed part in the engine, the piston."--Larry Bible

Larry has said this before... but I still can't figure out where he got this concept. It violates the physics of the situation with regards to Aluminum...
Aluminum is incredible strong in tensile strength... period.... and even more so if you look at it with regards to its weight....
It is like fiberglass in that respect... and in another... it is pretty much good until it is bad. It holds all it can then completely gives way... It does not typically weaken just from sustained use. If this concept were valid I propose that the MB Factory shop manual would say " replace on principle" as it has no qualms about doing with regards to other parts... whether they spec out correctly or not... because they are the type materials which are prone to weaken slowly and then give way.
This is where dial indicators, good magnifying glasses, and care in the inspection of engine components comes in... after the engine has been taken apart and you are making the decisions concerning what needs to be replaced, refurbished or whatever...
If the aluminum pistons spec out ok... or can be made that way with minor machining as with the wider rings.... there is no reason not to use them again... and many dollars worth of reasons TO use them.

When I rebuild an engine I always replace the pistons. The rods can be reused and / or reconditioned in most cases. Cylinders do tend to wear slightly out of round and on a taper. However To do it right…… the cylinders should be bored and honed. Thus, the need for replacement oversized pistons. 30 oversized will clean up most cylinders. In some cases you can sleeve the cylinders when there is excessive wear. Some manufactures allow for sleeving. Or if the engines are sleeved from the factory….Press in a new cylinder…
I have rebuilt a Ford 460 V8 In reasonably good condition. I did not bore or hone out the cylinders at all. I simply cleaned the pistons slipped on a new set of rings as per the manufacturer’s instructions. 45000 mi. later it runs great with no oil burning at all.
It certainly depends on the condition of the block. Check the cylinders with inside micrometers. See if there is a difference side to side and then 90 degrees side to side clearance and check for a taper between top and bottom.

“On my 240D I didn’t re-sleeve and I used Deves rings and a year later it blew oil like crazy.”

In this case the rings did not seat themselves. Rings come with a soft power coat layer on the mating surface. This wears away quickly to seat the rings. Some times if you hone the cylinder it just wont work. The rings wont seat. The cylinder needs to be near perfect. Understand that the now newly scratched honed surface will cause the soft powder coat to wipe off much too soon allowing for a fast break-in 20 min or so. So if the cylinder is slightly off the rings wont have enough time to break in. You will have better luck just wiping out the cylinders and replacing the rings. The smooth cylinder walls will allow for a gentile break in ….about 500 miles. The cylinders do need to be in good shape for this process.

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2003 SLK 230 (85000)
1999 E300 Turbo Diesel (388,000)
1991 350SD Turbo Diesel (185,000)

I will need this space....

.............what's the deal...........we have to wait until tomorrow..................

I was thinking about your statements regarding the pistons. The logic holds. Is anyone aware of a piston that has fractured after extended use in a 617? I would be interested in a situation where the pistons were reused after an overhaul and did not go the distance.

Sometimes I actually research the facts I use to support my opinions...and I knew I needed time but did not want my reply to be away from the subject post.

Don’t forget to have the tops of your pistons coated in ceramic it is cheap and you can increase fuel flow big time with out burning a hole in your piston. Furthermore it gives you a good excuse to put in that big intercooler while your at it have the turbo rebuilt with ceramic bearings and have the fans cut and bent for Evan more power so you only get 13 MPG you will have the only diesel MBZ that you now have to make a posi traction rear end to hook up all that power to the ground. And most important remember you can buy fiber glass fenders hoods and trunks for these cars.
Dave S

When you do research on the subject of pistons you will find that Mercedes coats them both top and sides with a protective coating. This coating will wear off …. Check for the piston skirt “scuffing” the cylinder wall. If it is, then replacement is necessary. If you reuse the pistons do not clean them ! Simply wipe them off with transmission fluid. If the “cross hatch” is still visible in the cylinder and there is no scuffing you can try just new rings. This is a clear indication that the oil was changed at regular intervils and that there is minimum wear in the cylinder. Also check for a ridge at the top of the cylinder a deep ridge indicates a cylinder that is well worn.
There are other after-market parts available as well. Usually when you purchase a replacement part you also get a “revised part” meaning an improved design. I would recommend checking to see weather or not there are improved designs available. From the factory or as an after market product. Ahh ....yes, newer designs have a ceramic coating. Older designs have a graphite coatingThere may be Matched parts available such as a piston / ring “set”. Also be aware that there may be a specific connecting rod that matches only that piston with “improved geometry”. A piston and rod set. Typical of most racing applications.
This is also true of the 603.970 diesel.

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2003 SLK 230 (85000)
1999 E300 Turbo Diesel (388,000)
1991 350SD Turbo Diesel (185,000)

" If the “cross hatch” is still visible in the cylinder and there is no scuffing you can try just new rings. " ---Anthony Cerami

Have you ever seen this concept written in a manual or rebuilding instructions for a diesel ?

My rule is " New rings , New crosshatching ". The function of crosshatching is to aid in the seating (wearing in ) of the new rings.

The exception is some air cooled small engines where chrome rings are available for rebuilding which are hard enough ( and typically work in aluminum bores ) to cut their own space.

" If you reuse the pistons do not clean them ! Simply wipe them off with transmission fluid."

Cleaning pistons during a rebuild involves getting any carbon off the top and cleaning the ring lands so that new rings can function properly. The instructions in the shop manual are very specific.

I feel like one of those teenagers who puts a spoiler on his Honda Civic, boy I guess I really didnt know that much..but then I always was a question asker, not a question answerer.

I do plan to rebuild this engine, because there will always be 123's I can stick it into. Just looking at it apart gives me a High. In the meantime I went to my indy and bought one from a wrecked 300D....and bought a car to boot. talk about shopping like a woman. I came home with a SAAB 86 Turbo 9000 5 speed for $400.00. The motor is good and so is the body, but it needs a lot of work...