I have an 83 300CD turbo diesel with 465,000 miles on it. My dad wants to rebuild this other engine that I have that was probably ran out of oil so one of the rods is probably frozen against the block. It's from a W123 300D turbo 1982. My dad wants to put it in my coupe so its faster and it doesnt get in the way.

My question is. Should I rebuild the 83 engine or the 82 engine? Are they the same?

Next question. I heard that you have to sleve every cylinder when you rebuild them, so, assuming that I sleve every cylinder what is the maximum piston diameter that I can use, and what is the factory diameter? What would be recommened so have enough sidewall left? I want to make a bigger bore to make it quicker, because if my dad is going to spend the money on something that he doesnt need to do, might as well have him pay my way into having the fastest 123 around. I want to have more low end torque, and also maybe I can get an intercooler and a different turbo. If anyone has light on the issues, could you shine it my way?

Thanks,

Austin

__________________
Current Stable:
1994 S500 v140, 210k miles, white with grey.

Former Mercedes in the Stable:
1983 300CD Turbo diesel 515k mi sold (rumor has it, that it has 750k miles on it now)
1984 300CD Turbo Diesel 150 k mi sold
1982 300D Turbo Diesel 225 sold
1987 300D Turbo Diesel 255k mi sold
1988 300 CE AMG Hammer 15k mi sold
1986 "300E" Amg Hammer 88k mi sold (it was really a 200, not even an E (124.020)
1992 500E 156k mi sold
etc.

About the biggest you can go oversize is 1 mm and find a piston that will fit. This will make a negligible difference in power.

You might stay with the original bore size and maybe you can use the same pistons. Pistons are very expensive for these engines.

If the engine was run out of oil, the crank shaft may not be regrindable. I think these cranks are nitrided so if you regrind it, you should renitride it.

P E H

I'm with P.E., I expect that the engine that ran out of oil will be more expensive to rebuild. I would rebuild the tired engine.

I would bore the existing sleeves and use the first oversize. I think P.E. is being optimistic when he says that the power gain from maximum bore size would be negligible, I think it would be completely non existent. You are not dealing with a gasoline engine here.

You can indeed sleeve it back standard, but with such high mileage pistons, I personally would not reuse them. I have on a shelf in my shop, my momento items, among them is a high mileage 616 piston with failing ring land. I caught it just in time. The pistons in a diesel are highly stressed items. For this reason, boring and using new, first oversize pistons is the most economical, practical way to go.

Good luck,

A competent machine shop can rebuilt the ring lands by installing a steel rings in the groves that will bring the piston back to almost new.

I always thought the idea of a sleeve was that it was replaced instead of boring it out. Maybe that is only for wet sleeves, not the dry sleeves that MB uses.

P E H

Yes, a wet sleeve is a whole different ball game. The beauty of the wet sleeve is that it can be pulled and the new sleeve put in its place without removing the block and sending it to the machine shop. It makes an in frame overhaul very complete.

The sleeve in the 616/617 is like the one that they use at the machine shop to repair a damaged bore in an integrally cast cylinder. When you replace one of these sleeves it is necessary to cut off the top and bore it to size. This means that when you sleeve back to original bore size, you will have a slightly larger bill from the machine shop than if you were to simply have the block bored.

I have had pistons serviced as you describe to bring ring to land gap back in spec. I have done this on gas engine pistons with good success. The problem is that the entire piston is under such great stress in a diesel environment, that I don't feel comfortable reusing it. That's just me. I've seen write ups by P.E. (I think) and others who have had success in reusing the pistons.

My $0.02,