My timing belt has failed early the last two times (93 Prelude VTEC - 223,000 miles). Service interval is 90k. It's failed at about 70k and this time 25k.
I found this thread that sounds similar:
timing belt slipping off cam *help please* - Honda Prelude Forum - Prelude Online.com
This time the mechanic showed be the belt that broke. It was much less than half the normal width. There was also black chewed-up-belt under the cover. (Amazing that it's so overdesigned that it continues to work with such a narrow belt.)
So it's been rubbing against something. Mechanic said he didn't see any marks to indicate rubbing. I assume the rubbing's happening slowly because I don't hear or smell anything.
Last time the belt was replaced with balance shaft belt, water pump, other drive belts, crank seals, cam seals, balance shaft seals.
This time the automatic tensioner was also replaced. I also skipped the water pump because it only had 25k on it. I also had a valve adjustment done this time.
Most of the engine compartment is factory original except for unrelated items like brake slave/master, clutch, radiator, some exhaust, ac hoses, etc.
(By the way, both times the valves were not damaged significantly enough to do anything. One was "slightly bent" the first time, but not replaced. This time they were just checked. The first time it broke when I was starting the car. The second I was going very slow or coasting almost to my driveway. It stumbed and died. Guess I've been lucky.)
Spending about $900 every couple of years is still cheaper than getting another car, but I'd like to understand why this is happening.
Mechanic said I should come back in a couple months to check the belt, which I agree.