Valve Timing

• The camshaft has a number of lobes that push down on the exhaust or intake valve to let air into or exhaust out of the combustion chamber at just the right time. If the belt has slipped a tooth or broken, the engine will most likely stall as the intake or exhaust valves will no longer open and close at the proper times to let air in or out of the system.
  
  

Non-Interference Engines

• If the timing belt breaks, the camshaft will cease to move and the valves will be stuck in whatever position they were in when the belt broke. Non-interference engines are designed so that the piston will not be able to contact the valve if the valve remains open when the piston is elevated to its highest position in its bore, so that no major internal damage can result.
  
  

Interference Engine

• If your vehicle has an interference-style engine, then the camshaft timing is vital. In an interference engine, the intake or exhaust valves extend into the cylinder bore enough so that the piston will slam into the valve if the valve remains open too long. If the timing belt slips or breaks on an interference engine, the cost of repairs can be high, as the repair can involve having to replace the piston or valve.
  
  

Preventive Maintenance

• To protect yourself from being stranded if the timing belt happens to break or jump a tooth, have the timing belt inspected regularly or become familiar with your vehicle's timing belt inspection procedure and do it yourself on a regualr basis. If the engine in your vehicle has an interference engine, it is advisable to have the timing belt checked often and replaced on schedule to prevent the possibility of serious engine damage.