mac , some got a lot of "Chainsaw effect" goin on , and again w/4cams some of the better designs are 1 crank chain powering 2 cam chains (ea. bank going off a "balancer shaft" occasionally) And all three of those are MUCH smaller diameter
and don't get G's beating the SH%&#@TT out of them , and harmonic vibes as much as ooooooooone biiiiiiiiig chain

Belts on the other hand , outside and pliable don't break off INSIDE motor. HOW many miles here though??