Timing belts

why are some engines designed so the timing belt can break without major destruction, and others aren’t. I’ve had experience with both. A '94 geo storm which we could change the belt on the side of the road, it broke so often, vs a’74 fiat which I sold, and later saw at a dealer with 1600 dollars worth of engine repair.

Many factors go into engine design. Weight, efficiency, power, noise, and others are all part of the game. Modern cars with timing belts have belts that normally last over 100,000 miles. Assuming you replace them as recommended, the chances of having a problem is low (not zero however).

Since timing belt breakage is so rare (at least, in a properly maintained engine), I would suspect that making an engine “freewheeling” is just not a high priority among engine designers, particularly if they end up with a design that’s less powerful, less efficient, or more expensive than an interference design. Some designers may deliberately move things around to get a freewheeling design, and in other cases it just may be a happy accident.

Could you literally change the belt on the side of the road with the Geo? We’re talking internal timing belt, and not accessory vee-belts, right? I find it hard to believe that the Geo’s belt broke “so often”, unless perhaps there was something wrong with a tensioner or something that was shredding the belt.

Could you literally change the belt on the side of the road with the Geo?

Not sure about a GEO…but I did on my 72 Vega. Broke on the interstate…I coasted to the exit ramp and down the ramp…then turned the corner onto a side street. A parts store was about 1/4 mile away.

More valve lift = more HP
More valve lift = broken engine if the timing belt breaks