Lots of good advice posted so far. I'm in the midst of a rebuild of my 500SL (Euro) and What it boils down to is you can do as little as necessary to get by. Or, you can make it a major undertaking. I took the latter route.

This involved:

- Having the heads shaved--mere thousandths of a mm, but I was told it was necessary.
- Replacing valve guides (cause of the rough idle and smoking)
- Replacing lifters
- Replacing rocker arms
- Replacing tappets
- Replacing camshafts
- Replacing camshaft stands
- Replacing camshaft sprockets
- Replacing timing chain
- Replacing rails
- Replacing water pump and thermostat
- Rebuilding power steering pump
- Replacing radiator shroud
- Replacing oil pump
- Replacing oil pump chain

Then, since the top of the engine is rebuilt and really tight, you potentially run into compression problems because of wear on the rings. In my case, I didn't have a choice of whether or not to replace the piston rings. After we got the heads off and found the worn valve guides, we turned the engine to look at the cylinders. The #1 cylinder wall was scored due to a busted oil ring. So we wound up tearing the engine all the way down.

I would have probably stopped with just redoing the heads if I'd had a choice, but I didn't.

As you say, it's an aluminum block...which requires different handling. We shipped the block to Renntech, which is down around Miami. They bored the cylinder and treated the cylinder wall with, I believe, nitric acid...which eats away the top layer of aluminum and leaves a silicone cylinder wall. (I'm in way over my head here, but that's what my mechanic told me occurs.) They also reconditioned the other cylinder walls.

- Replaced the #1 piston with one that is oversized
- Replaced the crankshaft bearings--after polishing the crankshaft surfaces with 2000 grit sandpaper
- Replaced the rings...which had to be specially cut and sent to England to be chromed. You don't want to use unchromed rings on the aluminum cylinders. Also, my mechanic says you don't reuse rings.
- Rings now have to be filed, since there should be a gap btwn .020 and .035mm when installed. Mine butted flush, which is no good. Mechanic has ordered a ring file, which will be in Wed.

- Previously replaced the injectors and seals
- Previously replaced the warm up regulator
- Previously replaced the fuel distributor
- Previously replaced all the air line hoses
- Previously replaced the fuel pump

I know I'm forgetting a bunch of what is being done, but it's an extensive job. Believe my mechanic said book labor is about 60 hours. I might be a bit off on that, but it's a lot of time. I've done much of the labor and there is a lot more to do when putting it back together.

All my parts are at cost. I'm providing much of the labor; he's providing the brains. And he's cutting me slack on his labor. No way I can figure how the job could be done cheaper.

He also told me yesterday that we will likely have to helicoil a hole or two when reassembling the engine--unless we get mighty lucky. It has one helicoil in it already that we noticed when disassembling the engine. Don't know if that one will inherently cause a problem or not.

Lots of lessons learned during this experience. There are also a lot of "gotcha's" in the disassembly and reassembly process. I've got the MB engine manual for the 117.962 engine. Without it, we'd really be struggling for a lot of the measurements and values.

This is not a job for the faint of heart.

__________________
Don
'85 500SL (Euro) - 186,000 w/a complete restoration and engine rebuild at 154,000
'95 C280 - 174,000