after disassembling my 82 300SD motor, I have discovered that the piston diameter near the top is excessively worn, as is the width of the ring grooves. Now, I am looking at another 7-800 bucks for a set of pistons I believe. If I do continue this project of rebuilding this motor I want to do it right, but I also want to keep costs under control as much as practical. What experience do you have as far as sources and brands in replacing pistons, rings and liners? The liners are already out and I will replace the main and rod bearings,seals, gaskets, timing chain and guides(preventively) and whatever the valve train requires C'mon talk me into doing it as I've put 80K on this car over the last 6 years and can see keeping it for 10-15 years more but I can't justify spending 3-4K fixing it.

What is usually done on an engine rebuild is you take the block to an automotive machine shop, they bore the cylinders or sleeves in your case, to true the cylinders, eliminating the effects of wear. Now your cyl.s are slightly over sized, which is why replacement pistons are available in slightly larger dia.'s commonly 20, 30 or, 40 over, as in thousandths of an inch. The more cly wear, the larger the bore becomes, hence the different sizes. This is not usually a big cost in rebuilding an engine, and restores it to new condition.

Since your sleeves are already out of the block, call a couple of automotive machine shops and ask them which is cheaper, to have them set up to bore them individually, probably, or in the block, which means you will have to put them in and haul the whole thing down there.

Hope this helps.

Pete,

$3000 to $4000 for repairs to a car that you intend to keep for another 10 to 15 years sounds inexpensive to me. If you bought a new car you would lose that much in depreciation in one year.

I know new pistons are ridiculously expensive for MB Diesels, but it looks like you might need new ones. Take the pistons to a competent auto machine for for evaluation. The ring groves can be rebuilt but I don't know about the wear on the top of pistons. Maybe you can use the pistons with new cylinder sleeves if the sleeves are machines to fit the old pistons. Talk to the machine shop people. They can tell you more about your parts by seeing and measuring them than we can here.

Try Fastlane or Parts Shop first to check prices. They support this site and usually have the lowest prices.

P E H

geat Boob may be onto something. They make two over sized pistons I believe and depending upon your wear that might be the ticket. I also thought that I read here that a lot of guys don't even do the bottom end in their motors unless there is signs of wear...
The MB cranks and bearings seem to hold up for a long time if they have been regularly serviced.

__________________
'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique

Contact these folks with all the pertinent information...

http://deves.com/ ( homepage......)

http://deves.com/devesrings/cars_MERCEDES_BENZ.html

tech advisor Maria@deves.com

These are the pros for options and great rings...

Your Sleeves are out.. I would go with the stock size pistons... The value of a normal car drops 3000 dollars a year.. So Buy another car today.. and on the first of next year even if you do not drive it it will loose 3000 dollars.. My 92 300CE the sets in the shop under cover went from 18000 to 15000 over night on the first like all cars.... Thats just the way it is.. If you spend 3 or 4 thousand... Drive the car 8 or 10 years you have saved your self 24 to 30 thousand over getting a newer car... Fix it right.. do a good job.. Do not cut corners.. Drive it 8 or 10 years and junk it.. You will be money ahead.. Check with Mercedes on price then base others on that price..

Ken

P.E. and Ken offer some paragraphs of wisdom. If you are planning on driving this car for many years to come, $3K or $4K is nothing to spend to get a solid engine in this car. Once you get a good engine in it, religiously keep up with your oil changes and other preventive maintenance and the 10 or 15 years will be no problem with the engine.

Secondly, I am amazed that you already removed the cylinder liners. Why on earth did you do that before measuring and researching?

Since they are out, and you know your pistons are bad, your only choice is to install new liners, top them and bore them to fit a new set of pistons. Had you not removed the liners you could have saved money by boring to the next oversize and replacing the pistons which you must replace any way.

Also, you said that the pistons were worn more at the top than the bottom. When cold the piston diameter at the top will always be more than the skirt area. This is to allow for expansion at the top. If the ring grooves are worn, this doesn't matter. These pistons suffer ring land failure from time to time, been there, done that. So, I wouldn't take a chance on reusing them with worn ring lands. Pistons in a diesel are a highly stressed item. If you want the engine to stay under you for the long term, just replace them and consider it a bargain when looked at on a cost per mile basis.

Look before you leap,

If you are really hurting for $$$ why not try to find a decent used engine in a boneyard? Here in NE the engines easily outlast the bodies of cars. You might even find a complete car that is unsafe and cheap due to rot but has a great engine. Look around, you might find what you need for under $1000. RT

__________________
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I agree with everyone in this thread so far... good ideas and attitudes...
One exception is that LarryB left out the word " might" in the third paragraph... "you might could have saved "...is what it should have read...
But, I think Larry is being a little hard on you even though technically for the most part he is correct... part of this comes down to philisophy...
For the cost of new liners,,,if I were going all the way to the innards of the engine like you have.. I would have done the same thing you are doing... because you would have to have it bored EITHER WAY.... but going back with new liners will cause the new rings to be riding where they should be rather than getting towards the outside of the piston lands...
I am interested in how you pulled the liners... and will be looking for your description of putting the news one in also... Greg

The reason I did not use the word "might" is that if the liners were still in place, it could be bored and o/s pistons used. If you insist on use of the word "might," then you MIGHT have had little enough cylinder wear that you would not have had to rebore at all. In that context, however, this is a very big "might."

The chance of the original bores not being worn excessively is remote at best.

Where I was not totally accurate was in suggesting only the "first" oversize. If all cylinders did not clean up at the first oversize, you could then bore to the second oversize.

And, yes, it would have to be bored either way, but since the pistons have been condemned, it makes no sense to incur the added expense of liners when you're going to have to replace the pistons anyway. Replacing the liners in this situation is nothing but extra expense.

Have a great day,

One item not specifically mentioned in this equation is this...
The 'BORING' which is done to bring a sleeve into compliance with respect to a piston which is going into it when one is using new sleeves is very different from what is "required"... for a sleeve with potential diameter/taper/concentricity needs...
A new sleeve can be done with a set of stones in an arrangement like a large brake cylinder hone... spring loaded, spring connected to the driving drill... etc..and cheap to buy...and easy to use by a DIY'er.
One with the aforementioned problems will need a set of stones held fast in a micrometer adjustable boring hone... the stones themselves likely costing as much as the other system... and needs a way to hold the centerline of each cylinder...
Now if this part of the job is being done by your machine shop then the amount they charge labor per hour may make or break this comparison... between the new sleeves.. and the old ones properly honed...

The 240D engine I had done last year ran $35/cylinder for removal/installation and boring of the sleeve which I thought was a very good price. This did not include the cost of the new sleeves.

__________________
Jim

If you are talking about hand honing a thousandth or two to fit the pistons, this can be satisfactorily done with a hand held drill.

The only way I personally would allow such honing to be done to my engine would be with a Sunnen CK10 (Cylinder King) or equivalent machine used by a competent operator.

The companion tool would be a boring bar that indexes off the main bearing webs of the block such as the Rottler. There are still some shops that use the old fashioned bar that simply sets on the cylinder deck.

The old fashioned bar and the hand held drill have no way of ensuring that the cylinders end up perpenidcular to the crankshaft centerline.

Regardless of whether new sleeves are used or you are boring to an oversize, ideally the cylinder should be bored with the Rottler or equivalent and honed with the CK10.

Most any well equipped shop will have this type equipment. If they don't you will have a longer lived engine if you find someone who does have it and knows how to use it.

Cylinders that are not perfectly perpindicular to the crankshaft centerline will impart stresses that the folks in Stuttgart, or any other engine designers, did not design for.

Good luck,

I should have been more specific when I started this thread. The liners all had a ridge of .3 to .5mm, that is using a decent telescoping gauge and verniers it was obvious enough to me that the liners had a good life and I removed them for exactly the reason that leathermang stated, i.e., I can hone the cylinders quite easily when I'm starting with a very even bore. Sitting on the ways of my old milling machine I can run the hone at a slow speed and achieve a nice cross hatch. If I can't, I have no business going any further. Moreover, I spoke with the people at Deves and realized my ignorance in that I had assumed that there shouldn't have been much difference in piston diameter from top to bottom. The pistons are about 90.21-90.28 on top, 90.5-90.55 near the pin and 90.84-90.87 at the skirts. As I was talking to them I also noticed that some of the space in the 1st ring groove was actually due to loss of ring thickness as #5 measured 2.84 to 2.87. Perhaps I will be able to use these pistons after all as Maria at Deves told me they can supply the first ring with a thickness of 3.17 compared to their standard of 2.98! Obviously, I will need to get the grooves recut square and true to obtain the recommended gap, but that's doable. First, I need to clean these pistons really well so I can get a better look at them. Oh, and by the way, the liners were pretty easy to remove. I made a tool based on the one shown in the shop manual, (but with a removable 1" shaft) and then I pressed them out on my arbor press.

I knew you would enjoy dealing with Deves... they were recommended to me by TCane....
Larry, although you phrased some of it to sound like we were not... I think for once we said exactly the same thing....