Rebuild/Pistons question - PeachParts Mercedes-Benz Forum

PanzerSD · #1 01-07-2007, 08:09 PM

I have a fairly clean running 617.950 in my '80 SD, and I plan a rebuild at around 500,000Km. I'm at 422,000 right now and it's original.

When it comes time to tear the engine down, what is the likelyhood of me having to replace the pistons? If there's no significant marring on the face or skirt of the piston I should only have to re-sleeve and re-ring right?

and Oil pump. Insanely expensive, is it re-usable after a rebuild? or can the pump itself be rebuilt?

I could possibly save $2000 on my rebuild if I don't have to replace the pistons....

and frankly, I can't wait to tear that thing down

#2 01-07-2007, 08:11 PM

I believe it's the ring land measurments that determine if a piston can be reused (assuming an otherwise good condition).

engatwork · #3 01-07-2007, 08:14 PM

FI is right. It is the ring land you have to be concerned with. Excessive ring land clearance = broken rings.

PanzerSD · #4 01-07-2007, 08:34 PM

so on my engine, at 400,000+ K it's probably unavoidable to have to buy pistons...

Tell me what you guys think about my engine parts shopping list....

Crankshaft bearing kit
Connecting rod bearing kit
Crank case/cylinder head gasket kit
Valve stem seals
Exhaust/intake gasket
Pistons
Piston rings
Cylinder sleeves
Timing chain/tensioner and related..
Waterpump
Prechambers
Injectors
Glowplugs
All new engine sensors. (cooling, oil, boost, ect.)
New main cap bolts
New head bolts
New connecting rod bolts and nuts

And of course, any crank/cam machining services and boring. I can do the assembly myself

What's the break-in procedure for a freshly built diesel? and can oversized pistons/sleeves be bought anywhere?

and feel free...if there's anything I should add or remove to this list please lemme know, and also any advise you can give me about rebuilding one of these engines.. I'm not an amateur rebuilder, nor am I a professional, but I can do it.

Chas H · #5 01-07-2007, 08:47 PM

New pistons don't require new sleeves. Get oversize pistons-after measuring bore wear-and rebore the block.

t walgamuth · #6 01-07-2007, 09:33 PM

i have rebuilt about five of these diesels. only once did we have to do any pistons. if they measure out ok then they are ok to use. replacing the sleeves and reusing the pistons is less expensive than boring and buying bigger pistons. and better imho.

the block should be trued to the crank too (they twist).

then you install the sleeves and bore it so that they are perpendicular to the crank line and hone to fit the pistons.

actually at that mileage you really probably could leave the bottom end alone and just do the head. often at that mileage the bearings and bores are fine...if the engine has had good care.

good luck

tom w

PanzerSD · #7 01-08-2007, 12:50 AM

Great!

that's what I wanted to hear.. saves me ALOT of cash...

#8 01-08-2007, 08:43 AM

Quote:

Originally Posted by t walgamuth

replacing the sleeves and reusing the rings

Whats the point of opening up the engine if you are going to reuse a cheap item like the rings?

t walgamuth · #9 01-08-2007, 09:15 AM

i meant to say pistons. we replace the rings for sure!!!!

sorry

tom w

ps i changed the above post. thanks for calling that out.

leathermang · #10 01-08-2007, 11:13 AM

You really need to get hold of a paper FACTORY SHOP Manual for your engine before you start the rebuilding....and frankly I would suggest you get and study it before starting to take things apart... some of the design is quirky...and even if you have done it before they often show THREE different designs for any particular component...which for instance can have a different kind of holding mechanism hidden behind it... get the manual to reduce the " Geez" factor and make this job more fun.

When you have the FSM it will tell you exactly the important GO / NO GO measurements to take ... to decide on what is needed for putting it back together properly...

There is one extra option which might save you money and still work well... except for Chas H ( who is thinking old American engine and has not seen the manual for these engines ) the above advice has been on the money as far as factory info goes...

But there are aspects of the piston land wear where you might could have a good machinist clean up the ( expensive ) piston and call the people at Deves.com
These are ring specialists and might could provide you with a deeper or wider ring to make the clearance in the cleaned up piston still meet specs... ( and save big money cmpared to those annular oil cooling ring pistons )....

Chas H · #11 01-08-2007, 12:56 PM

I have looked at a FSM, not recently. Is there a proscription against over boring the block?
By the time you guys dick around saving old pistons, replacing and finishing to size liners, ordering special rings of unknown quality etc. you'll be money and time behind simply overboring the block and fitting oversize pistons.

300SDog · #12 01-08-2007, 08:04 PM

Quote:

Originally Posted by t walgamuth

i have rebuilt about five of these diesels. only once did we have to do any pistons. if they measure out ok then they are ok to use. replacing the sleeves and reusing the pistons is less expensive than boring and buying bigger pistons. and better imho.

the block should be trued to the crank too (they twist).

then you install the sleeves and bore it so that they are perpendicular to the crank line and hone to fit the pistons.

actually at that mileage you really probably could leave the bottom end alone and just do the head. often at that mileage the bearings and bores are fine...if the engine has had good care.

good luck

tom w

Tom, your advice makes helluva lot of sense. Gotta blink at those who believe they can just toss in a set of *imballanced* oversized pistons..... thinkin they're doing the kinda work that matches Stuttgart specs. Hell, most people dont even realize the original pistons are ballanced to the rods and crank at the factory as a unit - and the process caint be duplicated without blueprinting the engine.

Meanwhile turning crank journals and installing oversized bottom end bearings strikes me as an equally crazy waste of time. Too many things can go wrong with a sloppy build and if these engines aint miked and ballanced to spec then they'll tear themselves apart.

GTB, if you want to entend engine life by another 200k miles (at least) after reaching the millenium halfway mark then replace the rings and you'll probly be good to go. But look for aftermarket SOFT METAL Swedish Rings! They make em specially designed to mate with high mileage MB pistons and bores that will not cut into the walls and cause piston slap.

And when you pull the cyl head then condition of valves and guides will speak for themselves. The general rule on rebuilding MB engines is that *less is better then more*. Notso long ago the #1 killer of 220Sb m180 engines was sloppy machineshop work where nobody knew how to even plane a cylinder head for a simple valve job within clearances without removing too much metal, thus over-compressing the chambers and then killing the rod and crank bearings.

t walgamuth · #13 01-08-2007, 08:47 PM

there is a shop in muncie that sells rebuilt mb blocks.

they simply bore them and install bigger pistons etc. they dont true the block or the bores. it is a lot quicker i suppose and they probably have figured out that it is the most profitable way to go, but me and my favorite machinist think our way is the better way to go.

he knows how to measure the parts. i don't. but they have to be measured and measured correctly. it takes a lot of time. he says he can do a sm block chebby in 1/3 the time.

we always replace the cam chain guides. often the chain is fine. if it is a turbo be sure to check the oil pump chain. either na or turbo check the oil pump too. sometimes we replace the gears in it. it all depends on the condition.

on my 280e last summer, the bearings and bores showed almost no wear at 143k but for some reason the oil pump gears were shot. (the new gears) one came from texas the other came from germany.

the parts are very expensive so we don't replace any that aren't worn beyond the service specs. well, we do if they are close to the limit.

good luck. unless i were very experienced i wouldn't do all these measurements myself. (and i am a very experienced hobbiest but not a professional machinist). i will go over and push out the sleeves and press in the new ones. that is simple and kindof fun. i also will clean things up. the last time i helped assemble i didnt torque the stretch bolts correctly and if his son hadn't checked it i would have blown it up when we put it in the car, so i dont assemble any more.

tom w

Hit Man X · #14 01-08-2007, 08:55 PM

Heck, you could buy a used 617 turbo (for parts) for less than the cost of one new piston.

Knightrider966 · #15 01-08-2007, 08:59 PM

A really good machine shop would come in really handy here! Do you know anyone you really trust in the business or someone who could give you a recommendation? You don't want to go cheap or just don't do it at all!

But that doesn't mean you have to go to a Mercedes Benz dealership either!