What Happens if the Timing Belt Breaks

Let's see what happens if the timing belt breaks on modern engines, which are almost always of the "interference" type. It is not just a problem of the engine stopping; it is catastrophic damage.

The belt keeps the crankshaft (which moves the pistons) and the camshaft (which opens and closes the valves) in sync. When it breaks, this synchronization is lost instantly.

Therefore, in interference engines, the pistons and valves share the same space, but never simultaneously: with the broken belt, the pistons continue to move because the car is in motion, but the valves stop following the correct cycle and can remain open: the rising piston then violently strikes them, bending or breaking them; the edges or heads of the pistons get dented, punctured, or destroyed; the valve stems bend or break; the camshaft can break if the valves get stuck.

In the most severe cases, broken valve stems can puncture the cylinder head, or fragments can scratch the walls of the cylinders.

Practical result: the engine seizes instantly and stops functioning. Repair requires complete disassembly of the cylinder head and replacement of all components.

The cost is so high that on not-so-new cars, it can render the vehicle economically unrepairable.