Originally Posted by
chunk t
I don't let gallons/liters or hours dictate when to change parts on an engine. I go by measurements. As the rod and pins wear the head clearance and port timings will change. Once they fall out of tolerance for my desired application, then the engine goes under the scalpel.
(if you didn't take measurements when the engine was new, you won't have any numbers to compare against) 
Tricky.... With onroad engines the material of the rod gets tired/weak what you never can measure (without damaging the rod). The rod can measure fine, maybe as new but can snap in a blink at the next time you start the engine.