Timing belt in my dodge neon broke recently, while we were at a stoplight. I took off the head expecting valve damage, but thankfully found none. After playing with the camshaft, I found that it is pretty hard to keep the camshaft position so that any valves stay open. It seems that the force in the valve springs keeping the valves shut is much stronger than any friction force keeping the camshaft in place. So, my thought is this: Timing belt brakes, loses tension, and immediately all valves shut as there is nothing more to keep them open. If that is the case, how could anybody be worried about valve damage? Unless they were at high RPMs and valves didn't shut in time, or the belt only skipped a few teeth and never lost tension completely. Any thoughts?

 

You were stopped at a stop light, i.e.- lowest engine RPM, lowest amount of force/pressure in the engine. If the car is stopped and the timing belt breaks, it is not uncommon for no internal damage to be done. If you are driving along at 3,000 RPM instead of idling at ~600 RPM, things in the engine are moving several times faster. Momentum and Newton's Laws still take place inside of a car engine. It's fairly difficult I'd think, to completely stop a piston (the whole rotating assembly) from moving and a valve from opening in less than a second at 3,000 RPM.

It basically comes down to the luck of the draw at idle. Damage can occur, but it's much more likely it won't due to the above.