When my Bullet was struck, and mangled, the Odometer had rolled over a couple of times, but it's easy enough to figure out, 100 Miles a week (which I did at the time) bought in August 1989, wrecked August 1992 = about 20,800 Miles.
The engine did about 2700 more than that after I dismounted it from the wrecked frame and hooked it up to a 1974 Tomos Koper rear with a 78 Puch front end (The frankenbike).
So, all in all about 23,500 Miles...and the Engine still ran when I moved and was forced to leave the frankenbike behind.
Frankly, I don't know ANY way to wear out a Tomos engine....if they ever made cars, the auto industry would be in it deep.
P.S. - You shoulda seen the dealers face when I brought it in for the free 3,000 mile servicing, less than seven months after purchase.