With an "interference" engine (like a Volvo "white motor"....or any Honda) if the belt breaks, the pistons will then collide with the open valves. This will bend/break/destroy the valves, and, if you're really unlucky, gouge a piston or two.

The Volvo "red" motors are mostly non-interference, meaning the car will just stop. Still, this isn't a good thing either, if it happens on an acceleration ramp when there is a fully loaded cement truck bearing down on you.

(The "red" 16-valve B234F IS an interference motor, also.)

Timing chains have been used on some engines, notably on 4 cylinder Saabs. They don't require periodic replacement. They are noisier and more expensive than belts.

Since a timing belt can break *without*any*warning* I'd replace it when the manufacturer says to replace it. Check your owner's manual, the 70k interval is only for recent "white motors"!!!! I believe the 21mm belt on the '92-'93 needs to be replaced every 50,000 miles!!!

-Uncle Olaf