I have been reading this forum over the past two months and have learned alot from it. What a great resource! I am a novice so be gentle if I ask some stupid questions.

I am about to have a shop resleeve my 617 block and I am trying to make sense of Cylinder bore dimensions that are called out in the MB W123 Service Manual CD.

There is a table showing piston diameter and cylinder bore.

Near as I can tell, if I use my Standard sized pistons, which I think are 90.90mm, I should have the cylinders sized within the following size range:

Cylinder 1: 90.929 - 90.938mm

Cylinders 2,3,4,5: 90.919 - 90.928mm

(The VIN of my 1979 300D is 617 912 12075931. A MB parts Guy told me that for engine numbers over 912 053946 the Standard sized pistons specified are 90.90mm dia. )

I would like to make sure I give the shop the correct specification for sizing the bores in the new sleeves that they put in.

It seems odd that the Service Manual would call for a larger bore for Cylinder 1 than for Cylinders 2,3,4,5. Why would this be? Is it correct? The pistons they call for are the same diameter across all 5 cylinders for a given Group Number in the table. I am guessing that my 617 engine is "2nd version", "Group Number 2" but I don't want to quess wrong!

How can I verify whether my engine is 1st version or 2nd version?

How can I verify what Group Number my engine is in?

Any insights are welcomed. Thanks.

- gburnett

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gburnett

1979 300D 250,000 Miles

Are you putting in everything new, new pistons and new rings and new sleeves also?

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Junqueyardjim
Christianity, if false, is of no importance, and if true, of infinite importance. The only thing it cannot be is moderately important. C.S. Lewis



1983 Mercedes W123 240D 4 Speed 285,000 on the road with a 617 turbo, beautiful butter yellow, license plate # 83 240D INDIANA

2003 Jaguar Type X, AWD. beautiful, good mileage,
Mom's car, but I won't let her drive it!

Take the pistons to be used to the machine shop. The machinist will measure each piston and size the bore for it.

What Chas H said (as long as it is a reputable machine shop).
I have been told that the difference in the bore size is because of the different heat transfer rate of the #1 cylinder versus the other four.

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Jim

I agree. Also the machinist can measure and examine the pistons to see if they are good enough to reuse. In about 3 of 4 mercedes engines we have rebuilt we have reused the pistons.

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.

I am putting in new sleeves and rings. I am hoping to reuse pistons. I am taking what I have to the shop for inspection so they can tell me what can be re-used with a reasonable chance for success. I know from reading other threads on this that I should probably spring for new pistons but my wallet is seized in my pocket on that one so far. Thank you for your replies.

I also appreciate the comments on why the cylinder bore is larger for the number one cylinder.

Thanks so much.

-gburnett

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gburnett

1979 300D 250,000 Miles

I don't know but know the difference is miniscule....like the thickness of a piece of paper.

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.

Here is a short backround on how this adventure started for me.

I purchased this 300D from a friend who had too many other projects going and had lost interest in the Mercedes. It had sat for about 7 years in his yard. He thought the car just needed a new battery and starter solenoid. I brought it home on a trailer and proceeded to put in a good battery, change fuel filters, plumb in a bottle tank and get the car to start and idle for a couple 3-5 minute intervals. Then BANG!, it put a connecting rod through the side of the block. Pulling that engine revealed a broken connecting rod bolt, a severely bent rod, a gaping hole in the upper oil pan and block, a couple spun connecting rod bearings, and when I removed the oil pump it was binding and hard to pull out. The shaft is frozen. I don't know if the connecting rod broke first followed by great contortion and bad things, or if the oil pump was frozen when I started and bad things happened from not getting oil. My friend gave me another siezed 617 that I stripped down both as an educational experience and to see if I could use the block from the second engine. I had the block and crankshaft from engine #2 hot-tanked and inspected. The shop said both are good and proceeded to polish the crankshaft. The crankshaft didn't need to be reground. The block had a deep scoring in one cylinder bore.

I am trying to assemble enough servicable parts to make a working engine without spending a fortune. I am not seeking a perfect rebuild. I know the general comments on the forum support the notion of forgetting a rebuild in favor of picking up a wrecking yard or parts car engine. I guess I am a bit of a glutten for punishment but I want the experience of going through the engine rebuild process, if I can avoid breaking the bank in the process. Silly? Probably. It's been mostly fun and interesting so far.

This is probably too much information but I thought it might provide some context for my other questions.

Also, I took a number of photos as I pulled engine #1 from the car and at various points in the disassembly of engine #2. I can post them to photo sharing server with a link if people think this would be of value.

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gburnett

1979 300D 250,000 Miles

Another question. The pistons from engine #1 have "Std" Spc. 0.3 pistons which if I understand it correctly means a 90.90 dia piston. The pistons from engine #2 have 90.97mm, Spc. 0.3 pistons. The ring set that I purchased is "Std" or for 90.90mm. My question is, do I need an exact match on the piston to ring size or is the 0.07mm difference negligible, such that I could mix and match the 90.90mm and 90.97mm pistons and use the 90.90mm ring set on both piston sizes? And you were starting to think that there was no such thing as a stupid question.

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gburnett

1979 300D 250,000 Miles

The rings should be end ground to fit in any case so I suspect that one size probably fits all in this case. To be sure ask your favorite parts supplier who specializes in mb parts if there are different part numbers available for the different pistons.

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.

Upon a closer look at the table from the Service Manual CD, it looks to me like there is a range of piston diameter from 90.98-90.90mm that are in the "Standard" category for the 617 engine. So I guess I am probably close enough with my 90.97mm pistons to use the ring set that I have for the 90.90mm piston size. I am going to the shop today with my collection of pistons and connecting rods so I will see what they have to say. Since they would size each sleeve to the specific piston that is intended for that bore, and since I would file to get the desired ring end gap, it sounds reasonable to me.

Here is a copy of the table I have been looking at. I am just learning how to post pictures.


By [URL=http://profile.imageshack.us/user/gburnett

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gburnett

1979 300D 250,000 Miles

t walgamuth,

Paper is usually .002 to .004 inch. This is NOT a miniscule dimension in an engine.

P E H

gburnette,

Check the width of the piston sring grooves, especially the top groove. If the grooves are worn wider and tapered, they can be machined and either a spacer can put in the groove or thicker rings can be used.

This costs much less than new pistons and the machine shop should be able to do it.

P E H

I did not say trivial, which suggests a value. That is your word. The context was a person wondering if the difference might make his engine vibrate, I believe.

In another context such as clearance between piston and cylinder, yes it can be very significant.

I said miniscule, which merely suggests a very small size.

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 what I have been reading, it sounds like you are fixing the engine the opposite way you should. What is normally done when rebuilding an engine is to buy new oversized pistons and rings (if available) and bore out the sleeves to match. They are called the repair sizes in the Mercedes parts book. If no oversized pistons are available, or the maximum size has already been put in, then you buy the complete set of pistons, sleeves, and rings and put it back to standard size. If the clearance between the piston is within exceptable tolerances (measured with a feeler guage between the piston and sleeve with no rings installed) as stated in the repair manual, you can get by with just honing the cylinder and installing new rings. This is assuming the rings fit tight in the ring grooves of the piston with no excess slop.

In your case where only one sleeve scored, that one sleeve only can be replaced and bored to fit the piston. But if there is enough wear in the pistons and other sleeves, you may need the oversized pistons or have all of the sleeves replaced and bored to match the old pistons. The latter method is what it sounds like you are trying to do. But do make sure the pistons are in good shape and the rings fit well or you are just wasting your money. You will need to buy the size of rings that match the piston, whether it be standard (STD) or an oversize. The size should be stamped in the top of the piston. The rings will be labeled on the package with the same size. I would not start mixing and matching sizes of rings and pistons if you want a good end result. The way I look at it, if you are going to put that much money into it already, do it right the first time.

As for clearance, this is always measured between the sleeve and piston with feeler guages which are longer than standard guages to fit along the entire length of the piston. The rings are not installed when measuring. The repair manual will tell you the recommended clearance. But a veteran mechanic with Mercedes diesels told me that on the OM616 and OM617 engines, the clearance should be 0.0015" for all pistons. That is what I use and have had not problems.

In addition, you will want the head and block checked for flatness, again based on the tolerances in the repair manual. If one is out of spec, you will need it milled or you may have trouble with blown head gaskets.