RST Engineering wrote:
snip

The other side of that coin is that bearing/crankshaft wear tends to become
exponential after a point in time when it departs from linear. That is, for
a long time (extrapolated by the manufacturer to be "TBO") the wear on the
bearings and the crank is linear. At some point when the bearings get to be
sloppy on the crank, the wear accelerates, and the faster it accelerates,
the faster it accelerates. If you want to play the crankshaft roulette
game, you extend TBO until the bearings start to make metal. Then you pull
the engine down, and if you are lucky, the bearings (the cheap part) took
the hit and left the crank journals intact. If you lose, you grind the
crank UNLESS somebody else played crankshaft roulette before you and the
crank had already been ground to minimums. Now you REALLY have a rough row
to hoe, in that you get to find a replacement crank ... which ain't cheap by
anybody's standards.


As Smokey Yunick said, the more often you rebuild, the cheaper it is.
Going much beyond TBO on an aircraft engine-or beyond what the
consensus says is the usual life on other engines, be they car or
boat-is fool's coinage. Dismantle, clean, mike and magnaflux.