Gas engines are lower compression, so there is less pressure on the bearings on the upstroke. Many manufactures make them less sturdy (along with the notion of disposable engines -- 100,000 and they've been thrown away anyway thinking), but the controlled explosion of the gasoline air mixture generated considerably more heat and pressure than a diesel burn -- diesel fuel is injected for a rather long period, up to most of the power stroke at full load, so the pressure and temp are lower, but maintained longer.

This long burn is the source of the higher torque, since torque in a piston engine is pressure applied to a piston top. The drawback is that the engine must be built considerably heavier to withstand the high compression stroke stress, particularly the crank journals and head. Along with that, the long burn actaully causes the piston crown to get hotter because the temperature of the burning charge stays higher longer than in a gas engine (unless you have detonation in the gas engine, that will melt the piston!). Turbo diesel always have oil cooled pistons -- there is an oil jet in the crankcase that sprays oil up into the piston, and the piston these days usually is a diecasting, with a rather intricate oil channel that runs the oil around the piston several times on the way out to transfer the heat to the cooling system rather than to the oil pan.

A gasoline engine can be made to last just as long as a diesel -- MB engines are famous for lasting forever -- at the cost of more weight and size. The mains on an M117 are actually slightly smaller diameter than a Chevy 350, but are almost twice as wide. I've seen 350s run 300,000 miles and more, but they are the exception rather than the rule. It's fairly rare to see an M117 with a bad lower end -- most go 500,000 or more in normal use without excessive wear.

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!