If it slips far enough the valves will hit the pistons.
That would be very expensive to fix.

Best Answer - Chosen by Voters Basically the timing belt connects the crankshaft with the two camshafts. This allows the valves to open allowing air into the engine at the right time. If the belt breaks then the crankshaft along with the piston and rod assembly will still move but the valves will be still. This can cause the piston to collide with the valves which can cause damage to the pistons, valves, and the entire head in some cases. There is a chance of nothing getting damage though. There are interference and free-wheeling engines. The difference is that free-wheeling engines has a space between the top of the piston and the bottom of the valve so if the belt did break then the valve would not hit the top of the piston