* Interference vs. Non-Interference Engine: Whether the engine is interference or non-interference dictates the outcome. In an interference engine, the pistons and valves are very close together. A broken timing belt causes the valves and pistons to collide, bending or breaking valves and potentially damaging pistons and cylinder walls. This is far more likely to lead to catastrophic engine damage. Non-interference engines have enough clearance to prevent this collision, resulting in less severe damage or none at all.
* Speed at the Time of Breakage: A broken timing belt at high speed is much more likely to cause severe damage than one that breaks at idle.
* How quickly the engine was turned off: If the engine was immediately shut off after the belt broke, there's a better chance of less damage. Continuing to run the engine after a break would increase damage considerably.
In short: While not *always* ruined, a broken timing belt in a Chevy S-10 significantly increases the risk of severe and expensive engine damage. It's best to assume the worst and have a mechanic assess the engine before attempting to start it again. The cost of repair after a timing belt break could easily exceed the value of the vehicle if significant internal damage has occurred.
