If your vehicle is fitted with a timing belt and is over 100 000 k.m you need to have it changed . The belt is a rubber belt that keeps your valve timing in sync with your piston stroke . When this belt snaps , in some vehicles the valves can hit the top of the pistons and cause major damage . On some models though , the valves spring back up in the cylinder head when the belt breaks and avoid this damage , this is known as a ' free spinning engine ' . If your not sure , check your service history or check with the previous owner to see if the belt was changed look for a sticker on the timing belt cover of your engine confirming that the belt was changed  . If your still unsure change the belt and bearings as a precaution . In a typical timing belt kit it comes with a belt , idler and adjuster pulleys , cam and crankshaft seals . Your vehicle only needs this service done every 100 000 k.m. some models every 150 000 k.m. but that is a lot to ask from a timing belt .