Giving 617 pistons a new life
 

Hi all, I'm curious what others have done to combat worn out ring grooves in turbo 617s etc where the Pistons are expensive and a PITA to find.

My pistons are all worn the same on my engine. .008 axial play on the top land, .004 on the mid and .002 on the oil ring. While 2 is acceptable, the other grooves are just too far gone. I've found that there are 2 options to fix this without buying a new piston, and both involve a lathe.

Option 1 is to get shimstock spacers which are just a few dollars a piece, standard sizes are .016 and .030. so just add the thickness of the shim and the ring, add a thou and a half to that for clearance and cut the groove to that size. Bingo.
The only worry I have is how this affects ring seating during the break in period. Probably not a worry really because they're put on top of the ring, while 90% of the impulse is being transmitted through the bottom of the land. However these small considerations are necessary when you want them to outlive yourself.

Option 2 is to have custom rings made that are x units taller. The main problem is that there are only so many available sizes, so you can't just add a 'couple' thou to the height, more likely to add something like 30 at least at a time, if you're lucky. What I don't like about this is the increase in frictive surface, which is a huge factor in cylinder life.

When I add the future hauling of ass many times around the earth into the equation, I just feel like I want to get these things right. Don't take anything I say as verbatim, half of this is talking out my ass 😁

Feel free to bash my logic where necessary

Option 3 is to buy them new. Pricey but they are available if you have $$$

https://wahl-spezialkolben.de/en/


If you want to "cheap out" or skimp, I would not suggest doing so with the pistons. You can also get a decent used engine (complete) for less than the cost of a set of new pistons, so that is an option if money is tight.

recycle,and malhe makes custom pistons

Interesting idea .

I don't think pondering viable alternate solutions and thinking out load is talking out your butt .

I just bit the bullet and bought new pistons, ouch .

Apparently new OEM pistons are now available from an online vendor at $1850/set.

I got a few quotes for custom forged pistons, at around $1500/set, including rings and new wrist pins. If I couldn't find used pistons, they is the route I would take.

Where can you find forged pistons? I was under the impression that they had to be cast due to their hollow crown. Also, the top ringland is cast iron which I'm not sure can be easily replicated.

Of course oem pistons still exist, but I'd much rather do a reasonably priced fix. What problems do shims pose to the longevity of a piston? Aside from the lands they're like new. No skirt collapsing, wrist bores are spot on, they still have a nice outer finish with no scuffs. Im thinking I'll do the shims, if I do I'll post here

This was a few months ago, there are a few shops around me that make custom pistons. This shop specialized in pistons for high HP builds, and had quite a few sets in stock for high HP diesel trucks. When I called, they told me that they had "made a few sets of Mercedes 5 cylinder pistons over the years" - not sure if they made their pistons using the NA design, which doesn't have the oil squirters. I imagine the oil passage within the piston probably isn't as necessary with forged pistons vs cast.

OEM pistons were not available for a long time. I was able to find one NOS piston on eBay, sold by a dealership in Florida liquidating their old inventory. I would avoid shims, but that's just me. I don't feel like a shimmed piston would hold up as well. I am not an engineer.

One of these days I'm going to put the "NA" pistons in a souped up .952 engine and see what happens. Yes, I can hear why I shouldn't do it already...but these engines are that overbuilt I think I would get away with it.

It's possible to still get a good used OM617 just ask if they will let you do a leak-down test before you buy and you should be able to score a good motor for reasonable money

I believe Mercedes did that when developing the turbo 5 cylinder and the results caused them to implement oil squirters and the turbo pistons.

For the non-turbo 617 and late 240D's there was some company in Taiwan that made pistons for them and in the past there was ebay sellers that sold them.

for OM616 and N/A OM617 you can still buy pistons on ebay or on this website:


https://www.pelicanparts.com/catalog/SuperCat/3203/MBZ_3203_ENGPIS_pg1.htm#item1


they are not chevy level cheap but they are available

This is in no way a recommendation just some info from the past that I came across.

When I was taking tests to try to get a mechanics job for various cities I used some of the tests that the local main library had to practice with.

Some of the tests had a question about using a ad on thin piston ring and the question was what position did it go in.
The position was on top of the Compression Ring (between the compression ring and the top of the piston in the ring groove).

I don't think that would work on a Diesel Engine because a thin piston ring might get burned through.

I also think that question is from like the 1920-1930's because that info is not even in my Fathers 1948 Mechanics Trade school manuals. And that is back when they were still vehicles with pored in Main Bearings and so on.


Don't know what forum it was on but someone mentioned custom made piston rings although they were not thick they were made to have beveled gaps.

Just for laughs how to make a piston ring for a model engine

How To Make Piston Rings

I built a low deck block for a Dodge Duster.To get the longer connecting rod in the short deck block,the pin height in the Piston was raised up(compression height) to where the rings actually were located thru the pin bore.It required a ring support such as you mentioned.It was a disaster.I never did get that set of rings to seat properly.