Michael:

Have the crank checked for taper and roundness as well as size of the journals, rod and mains. If there is anything out of tolerance, you will need to have it ground, polished, and balanced (which requires the pistons, alas).

Just don't spin the pistons in the bores -- up and down won't hurt anything as long as the rings stay in their usual range -- don't push them into or past the ridge at the top. They go up and down a lot when the engine is running.....!

If the the crank journals look nice and clean, with no scratches or wear marks, you are probably OK -- my brothers (and the one in the short block he bought) was OK, but the bearings weren't right, so were shot. Minor imperfections can be polished out without grinding, so long as the diameter isn't greatly changed (as in still within stated tolerance). If you don't know how to use a micrometer, have the measuring done by someone with a metric mic set, no SAE with "translation" -- it isn't accurate enough.

Scratches imply dirt, and that in turn implies crank damage. Sorry.

All you need to do if the pistons have to come out is put new rings in after cleaning the pistons. Check ring clearance (side to side), although if the crosshatching is fine, I cannot imagine the pistons are worn. The the wear is less the 0.002" (a ridge you can distintly feel, no more) at the top of the cylinder, you don't need to do anything except maybe "deglaze" with a ball hone (have a shop do this, specify no diameter change!)

You will still have oil pressure problems with new bearings if the crank is bad, so you will have to decide what to do. If it was run out of oil, there is enough babbit on MB bearings to save the crank at the cost of ruining the bearings, so you are probably still OK, and will have proper pressure.

If you don't want to re-do the crank, get some plastigage and check the bearing clearance with it -- the smaller the better above 0.0005" -- you may have some trouble getting the proper size, as most auto supply places hire help who think Chevy 0.005" is about right!

Good luck!

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!