As most of you know, I've got the head off the 617 and need to replace it due to cracking on three cylinders, directly above the combustion chambers.

The question that I have is related to the condition of the cylinders.

All cylinders appear to have a slightly smaller and rougher surface for the first 1/2" or so, measured down from the top of the block. It appears that there is a parting line at this 1/2" point that is very slightly smaller than the remaining liner. Above this line is a noticeable difference in the surface. I've polished this surface with 1400 paper and have improved it significantly, but it almost seems like some corrosion has occured here. It does not seem random, however. All cylinders show this to a greater or lesser degree (the rear cylinders are the worst) and the surface deterioration suddenly stops at this 1/2" point down from the top of the block.

Anyone familiar with such a phenomenon and can provide some advice?

I may be able to get a photo of same, but, it's very difficult to see after polishing. It can be felt, however.

the top 1/2" is the part of the cylinder that the rings never touch because they sit 1/2" below the top of the piston. anything above the top reach of the rings is simply there, and the only thing it does is contain the combustion and hold the head to the rest of the block. what you have done already is about all that you can do. the important thing is the condition of the bores below.

did you ever say how the head got cracked?

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Thanks Tom. That makes perfect sense. I'm polishing the corrosion for nothing.

I don't think that anyone can say why it cracked, other than to conclude that somebody overheated it at one time in the past.

There is a very fine crack, directly in the combustion chamber on three of the cylinders. The cracks are so fine, they almost look like casting flaws. Apparently there is a coolant jacket above the face of the head. Cooling was passing through the cracks as evidenced by corrosion leading from the tip of the crack.

I'll see if I can post some photos of it today. I'd be interested in your thoughts.

If you ever do remove the pistons from the cylinders you have to borrow (or buy) the proper tool to remove that off of the cylinder walls prior to shoving the pistons through.
Can you see any cross hatching on the section of the cylinder below or does it look like a mirror?

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Jim

Yes, I understand from the gassers that this is the "ridge" and a "ridge reamer" is necessary to get rid of it. It just looked awful strange on a diesel. No real "ridge" to speak of. Just a very slight reduction in diameter that can be felt but not easily seen. Makes perfect sense once Tom posted it.

The bores still have cross-hatching. There is no mirror finish that I can see, but, my lighting is not all that great.

Another one of those deals where MB is different from all other cars which I have seen....They intend and expect that cross hatching to remain for oil supply to the rings or something....

If your bores were worn mirror smooth as you would expect of other engines MB would consider them worn OUT.

I have never heard of " choke " being called for in boring or honing a cylinder bore.... and MB certainly does not call for that.

I have heard of " choke " being produced by the differential pressure against the walls of the cylinder due to crank throw. But that is something measured and if too much is used as " needs reboring" measurement.

It looks as though the engine is coming out of my 300sd (although probably not until next spring). It makes no sense to me to have the thing on the stand and not "go through it". I will be certain to follow the MB manual to the letter, but as a matter of curiousity, do you not hone the cylinder walls. I was taught, that this was SOP, to help seat the new rings, and I have always done so. If, in fact, there is a crosshatching that is meant to be there, honing might not be the smartest thing to do. Any comments??

Thanks,
Jim

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87 190D - 225K (on loan)
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I have been successful in leaving the pistons in if the cross hatching is in good condition. If there is a mirror finish you need to resleeve, bore and cross hatch.

I've got a block for sale if anyone is interested. It will need to be resleeved.

617 block for sale

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Jim

sounds like you have very little bore wear. good deal.

tom w

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

From the looks of it, I would guess that it's less than .001. I have no qualms about putting it back together as it is.

Some engine manufacturers, such as Cummins, clearly tell you to NEVER hone their cylinder walls.

Humm, speaking of bore/hone. I wonder how many more cc's one would gain using 1st/2nd oversize pistons...

Figure it out. 0.7854 X the diameter squared X the stroke of each of your oversizes. Then subtract the standard volume from each of them and you have the additional cc's for each.

__________________
1983 300-D turbo
1985 300-D turbo
1959 Harley Panhead chopper
1929 Ford coupe restored
I hang out with Boneheaddoctor at Schuman Automotive OBK#5
All liberals are mattoids but not all mattoids are liberal.

You are right Leatherman about the cross hatching carrying oil. We recently had a job in our shop to re-sleeve 9 cylinder jugs for a huge air compressor. The low pressure jugs were 8 1/8" bore and the high pressure side was 7 1/16" bore. The jugs had to be bored over size to accept the new cans. After the new cans were installed they had to be bored to .004 undersize then honed to size. The factory recommendation for the finish surface was 70 grit stones. I thought they were nuts until I understood their line of thinking. The oil not only lubricates but it helps to seal the high pressure air on this beast. On car and light truck engines we are happy with a 280 grit stone for finish. I never saw a new Mercedes sleeve and I wonder what finish the factory uses.

__________________
1983 300-D turbo
1985 300-D turbo
1959 Harley Panhead chopper
1929 Ford coupe restored
I hang out with Boneheaddoctor at Schuman Automotive OBK#5
All liberals are mattoids but not all mattoids are liberal.

unfinished. you install the new sleeves, with the tops sticking out of the block, deck them along with the block, flush and bore them to size. they come undersize. this insures that the new bores are exactly perpendicular to the face of the block/head. dont know what grit they are honed. but i am sure it is a cross hatch pattern.

tom w

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

tom- Do you know if they are a flanged sleeve and what the wall thickness is? It surprises me that Mercedes has the installer bore and hone. I would have thought that they would want to do this rather than trusting the finish to anyone. When you say that it insures that the new bores are perpendicular to the block/head I am also assuming that Mercedes recommends that the boring machine be centered from the top deck which is where our shop's older machines center. The newer floating column boring machines center from the main bearing bosses. As for the cross hatch pattern our shop tries to get as close to a 45 degree pattern as possible.

__________________
1983 300-D turbo
1985 300-D turbo
1959 Harley Panhead chopper
1929 Ford coupe restored
I hang out with Boneheaddoctor at Schuman Automotive OBK#5
All liberals are mattoids but not all mattoids are liberal.