He hasn't told what caused the damage. Zero compression and marks on the pistons from the valves, would only indicate one thing, that the new timing belt somehow came loose allowing the belt to jump resulting in bent valves. I was told I had to change the timing belt by my mechanic. It is a mileage as well as a time factor when to change the timing belt. Under the circumstances, your car being a 1992, your mechanic is right.
Timing belts get old and thus become brittle and prone to crack.
Hi, I live in Moscow, Russia. I have Grand Am quad 4 1990. I do everything by my own hands. My problem is a noise when the engine runs at 2500-3000 rpm. Your noise could be caused by the timing chain guides and tensioner if they were not changed with the new timing chain.