I'm guessing that engine was not built with the expectation of it running for 100,000 miles.I did not count the teeth but it seems several cogs are the same size. Certain death there. In a cog train the teeth count need to be different so one tooth doesn't always land on the same spot...
And is this much different than say my Sportsters with four cams all timed with the same size gears? One of which has just a bit under 90,000 miles on the cams installed at 29,000 and those were replace due to damage from a failed lifter bearing.