Steve:
The pistons are expensive because they are both precision die cast (with a steel ring for the top compression ring to sit in) and extensively machined for the oil cooling system -- there are oil jets in the block that spray oil onto the bottom of the piston around the rod to cool the crown. Otherwise, they would melt under high load.
When you get it apart I expect you will find evidence of badly siezed rings having chewed up the cylinder walls. The pistons may be OK, but I'd not plan on it. To check them, inspect the ring lands carefully. Any visible of palpable evidence of a "lip" extruded out from what should be a nearly square edge of the ring groove means the piston is no good. Ditto for scuff marks larger than one third of the skirt area, or any place except the thrust faces. Any other damage (burns, melted areas on the crown, etc), condem them.
If they are visually OK, get a new set of rings and check the side clearance on the ring grooves with the new rings. If over the wear limit, get new pistons.
You have a choice if you need new pistons: bore the existing liners oversize (if they are thick enough) and fit oversize pistons, or press them out and install new ones, then bore to standard size and get new standars size pistons.
Just running down the road and it quit, eh?
Wonder if it ran out of oil first or overheated first?
Peter
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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!
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