why do some engine maintenance cycles run off hours, like generators, but others off miles, like cars? (Besides the obvious)

Question

why do some engine maintenance cycles run off hours, like generators, but others off miles, like cars? (Besides the obvious)

In: Engineering

Answer 1

The reason is actually pretty simple – “What measurement best estimates the wear?”. If we look at a forklift(tracked by hours) vs a car (tracked by KMs). The forklift is generally not covering great distances and a lot of the stress to the engine is coming from running the hydraulics (which means the tires dont need to be moving to be wearing the engine). The car on the other hand stresses the engine through running primarily the drive train, and so distance traveled is a better measure than the number of hours the engine was running.

I have never actually never worked with maintenance schedules for long haul trucks, but I imagine they would have a combination of the two (5,000 KMs or 250 hrs, whichever hits first), since they idle enough to require taking that time into account on the wear.