As long as the oil is changed regularly and there are no metal traces in it the crank should go well past TBO without undue wear. The camshaft is a whole different story. As the lobes are exposed (unlike the bearing surfaces on the crank) the oil tends to run off them if the engine is unused. They corrode and when started up after a long idle period wear rapidly. In addition, during long periods of idleness, the piston rings can "set" into a position and you lose compression. Exhaust valves tend to stick for the same reason. All in all, an engine that is not run regularly stands no chance of reaching it's TBO. Reckon on £800 per cylinder for an overhaul.......
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When the wheels stop turning you're high enuff. CubTrek. To slowly go...