An interference engine is a type of 4-stroke internal combustion piston engine in which one or more valves in the fully open position extends into any area through which the piston may travel.
Intake and exhaust valves are responsible for controlling the flow of gases through the combustion chamber. Intake valves let air in, whereas exhaust valves let air out.
If the timing belt breaks, this will mean quite a lot of damage to your engine and its parts, especially if you have an interference engine.
A broken timing belt means that the valves do not have the necessary time to close before the piston arrives. Because of this, a collision will occur between the pistons and the valves. This collision causes the valves to bend.
From the moment the timing belt breaks, the camshafts stop immediately, under the action of return springs that slow down its cams.
The crankshaft, at this moment, inertially continues to rotate (regardless of whether the transmission was switched on or not, the speed was low or high, the flywheel continues to turn it). Thus, the pistons continue to work, and as a result, they will hit the currently open valves.
Reasons why a timing belt would snap:
• A most common cause is a bad or failing water pump.
• A worn belt.
• Possible damages to the crankshaft.
• The belt loosens or tightens because the tension rollers are unscrewed.
Considering the valves, modern engines are much sensitive regarding this problem because of the small distance between the valves and the pistons. So, if the valve is slightly open when the piston arrives, it instantly bends.
Ask your specialists at VAG Spec Centre to check the condition of your timing belt regularly, to prevent bigger damage.