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Bamboo77 12-19-2000 01:45 PM

as many of you know, i am rebuilding the engine in my 1977 240D. i thought i had all the info, and all the advice i could possibly need in order to do this. i think i was wrong. today i recieved an email from a man with whom i have been coresponding about parts. he told me to NEVER, EVER rebore the sleeves in my engine and replace the pistons with oversized ones - which just so happenes to be what i had planned on doing - because the sleeves will crack. he said that i should resleeve the engine and use new regular sized pistons - much more costly. i do not know that this man has ever done a rebuild on one of these engines. i have heard good and bad about both ways of doing this. it seems more logical to me though to get new 1st o/s pistons, get the existing sleeves bored (a mere .25mm increase) rather than to use the old 240k+ mileage pistons, or to pay an additional $500+ for new std pistons. i need to know exactly what to do in this situation! please help guys! i would love to use new o/s pistons and my old, rebored sleeves, therefore cutting the cost of installing new sleeves. if anyone out there has ever done a rebuild the way i would like to do it succesfully, please let me know. thanks guys,
william gum

Benzmac 12-19-2000 08:54 PM

I have resleeved with the old pistons and had really good results.

We did this a number of times without problems.

Bamboo77 12-19-2000 09:08 PM

thanks. but what i want to know is if i can use the existing sleeves and insert new 1st o/s pistons? LarryBible and Wm. Lewallen have both mentioned this as a great alternative to reusing old used up pistons, and i wouldnt question it; but today i got an email advising me not to do so. if anyone has used this approach with success please let me know. thanks again,
william gum

Wm. Lewallen 12-19-2000 11:53 PM

To Bill Gum, Yes you can bore the sleeves that are in your car for oversize pistons. Lord knows how many I have bored for oversize pistons. If you couldn't, why do you think Mahle would make them. Yes, Mahle makes the pistons used in Mercedes.Make sure the 1st oversize will do the job.0.25mm is not much, something like 0.010in. I have even bored gasolene engines for oversize, and they don't have sleeves.
Keep us posted on you progress.
Bill Lewallen Lexington,Ky.

LarryBible 12-20-2000 08:43 AM

Boring the existing sleeves to the 1st Oversize is a common and successful practice. The persons opinion may have been formed with other sleeved engines, probably wet sleeve engines.

I think you should get your pistons, take them to your machinist with the block so he can fit them when he bores the block, and live happily ever after.

Good luck and Merry Christmas,

Wm. Lewallen 12-20-2000 11:33 PM

reguarding pistons
To Bill Gum, If you want to save money rebuilding your engine, You can install new sleeves and have them bored for you std. size pistons. You can buy the sleeves for about $21 each. Rings are about $27 per cylinder.If you can go this route,the grooves in the pistons must not be worn too much.
Here are tolerance limits for your pistons;
Top groove side clearance--0.100-0.132mm when new.
2nd groove side clearance--0.070-0.102mm when new
3rd groove side clearance--0..30-0.062mm when new
Wear limits:
Top groove--0.2mm
2nd groove--0.15mm
3rd groove--0.10mm.
The wear limits are the figures that you should be concerned with . If the grooves are too wide,then you must use new pistons,or you can have spacers installed in the grooves and have the grooves machined to the new limits. I have always installed new pistons because there is not a machine shop in Lexington that I would trust to do this close tolerance job. You may be more fortunate where you live. You can check it out. Keep us posted on your progress.
Bill Lewallen Lexington,Ky.

Bamboo77 12-21-2000 12:16 AM

thanks for all the great help so far bill and larry (and all the various others...). i am sold on the new o/s piston approach, and have already ordered 4 brand new 91.25mm pistons. here is my newest concern. i was browsing through my MB shop manual, and noticed that the cylinder bore sizes for the cylinders differed. cyls. 2-4 are the same size, while cyl. 1 is .01mm larger than the others. why? since you fellows havnt mentioned this so far, i am inclined to believe that it doesnt make much difference. if someone can furnish me with exact bore specs for all 4 cylinders w/ new 91.25mm pistons so that i may then transfer them to the machine shop i would be most greatful. and, if it makes no difference what exact size the cyls. are bored to as long as i take the pistons to the shop so that they may bore accordingly, please notify me so that i may stop my incessent worrying. thanks again guys:)
william gum

LarryBible 12-21-2000 06:51 AM

I expect that your new pistons will all be the same size. Just take them all to the machine shop and let them measure all four to be sure. Then they will fit the bore size to the pistons. No worries.

When you're into a job like this, your chance of success is greatly increased when you "worry" about these details. It's the person who doesn't give these things a second thought that ends up with lots of problems, so keep on "worrying". Attitude is everything.

Good luck,

Wm. Lewallen 12-21-2000 03:13 PM

Larry is correct. Let the machine shop measure each piston and bore each hole to fit each piston. I will number each piston and have the machine shop fit them accordingly.They may vary slightly in size.There is only 0.002in. difference in the diameter of the cylinder and the piston.That's only 0.001in. on a side, so it is a little bit of importance to have each piston fit to a specific hole.
Do you have a good torque wrench? You will need one, and do you know what the manual means when it speaks of "angle of rotation". I want to help you in any way I can.Just let us know what you need.
Bill Lewallen Lexington,Ky.
I have owned and rebuilt too many Mercedes to list here.
Lets just say I've owned a few.

Bamboo77 12-21-2000 11:10 PM

sure, i have a great tourque wrench. i'm not familiar with angle of rotation though. please offer insight. thanks

LarryBible 12-22-2000 05:47 AM


Do you have a manual to give you torque sequence and values? It sounds like you don't. Does this engine have star headbolts or hex(allen) headbolts? If you don't have a manual let us know and we will give you the information you need. The sequence will be difficult to verbalize here without a picture, but we can probably work through that.

Basically the torquing of star headbolts consists of this general procedure:

Clean threads on holes and bolts and oil bolt threads. Torque the head in sequence to the first setting, probably about 30 ft/lbs (I don't have my book with me) then torque to the second setting in sequence which I believe is about 52 ft/lbs. Let it sit for ten minutes and turn each bolt, in sequence, 90 degrees. Let it sit ten more minutes and turn each bolt again 90 degrees in sequence.

You will need a breakover bar for this, and be prepared to be very tired after this accomplishment. If you use a cheater pipe on the breakover bar, I promise not to tell anyone. The first time I did it, I went back to mercedesshop and called my friend the MB tech to see if these bolts were really supposed to be this tight.

The first one I did was my M103 engine. The bolt and hole threads were in great shape. I oiled the bolts before threading them in. On my daughters diesel, there was one bolt that was very stubborn coming out, so I got a tap and die, I believe the size was 12 x 1.75, but check yours to be sure. I ran the tap into every hole, and really messed around with the hole which gave trouble coming apart. I then stuffed a rag in each cylinder and blew out each bolt hole.

I chucked the die in the vise and ran every bolt in and out of the die. Since you're block is going to the machine shop, they should thoroughly clean the block after the machine work. It would be a good idea to chase the bolt hole threads before taking it to the machine shop, so all chips or crud that is loosened will be cleaned.

You can make a poor boy's thread chaser by taking a bolt the same size and thread, and file a couple of notches lengthwise through the threads with a three corner file. Make sure you clean the bolt before screwing it into the block.

Sorry for the long windedness, but you sound like a guy who is hungry for all the information you can get. I certainly relate to that. If I'm giving you more info. than you want, just tell me to pipe down.

If I were there and had plenty of time, I would enjoy helping you.

Good luck,

Bamboo77 12-22-2000 11:26 AM

we've got block problems fellas. i just got the call from the machine shop who had just miced my cylinders. the ammount of taper is (drum roll please): .02in i'm not sure what that translates to, but i was informed that the cylinders would have to be bored at least a whole mm; which is too much for o/s pistons of any kind, and would probably make the liners too thin anyway. any advice in this situation would definatly help. the shop isnt open again till tuesday. thanks guys, and merry christmas...

Bamboo77 12-22-2000 11:39 AM

ps to my last post
can you guys give me a general estimate for installing and boring new cyl sleeves? looks like thats where this thing is headed unless you argue the fact that a .02in taper warrants a 1mm bore. thanks,

patsy 12-22-2000 02:09 PM

I just want to mention, that you should find out which cylinder head bolts you have, and make sure they are not stretched too much to be reused. If they are, you have to replace them.

Wm. Lewallen 12-22-2000 03:14 PM

Since you have already gotten the pistons of 0.25mm oversize and the wear(taper)on your cylinders is 0.020in(about 0.50mm)you won't be able bore your sleeves.You will have to put in new sleeves and have them bored to fit the new pistons you have. If you can get the dealer to exchange them,do so and get std. pistons. They should be somewhat cheaper. You will have still to install new liners(sleeves).
The angle of rotation refers to the additional torque you apply after you have torqued to the specified amount. Set your wrench to the 12 o'clock position and turn to the 3 o'clock position. It is used on the stretch bolts. You should measure those bolts to make sure they are within specs. Simple. Keep us posted on your progress,and have a Merry Christmas.
Bill Lewallen Lexington,Ky.

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