Back in the old days, cars had timing chains. The chain controls valve timing using a few gears of different diameters. The chains were very strong and very rarely required service. In the quest for better fuel economy and less expensive manufacturing costs, many manufacturers eliminated the timing chain in favor of a rubber belt. The belts were less expensive to mass-produce and they performed slightly better. The rubber timing belts were not as durable and required periodic replacement (much to the delight of the dealership service department). To make matters worse for the consumer, many of the manufacturers also require that several other parts be serviced in conjunction with the belt. This takes costs even higher and adds to the “planned maintenance checklist”. And, as a final insult to the folks who bought a vehicle with a timing belt, if the belt fails the engine could sustain substantial internal damage sending costs even higher!
Unfortunately- Timing belt failure is one of the most common failures we see here in Eugene. The rain and the wet are hard on timing belts for some reason. We see many more failures here than we expect to. I strongly recommend replacing timing belts at, or even before, the manufactures recommendations. I advise my clients that if your timing belt has 8 years or 100,000 miles on it, they should replace it as soon as possible. In most cases the replacement cost is dramatically less if the belt is replaced before it fails. The belt itself costs less than a tow truck ride almost every time!
When the timing belt brakes the engine will immediately stall. The belts job is to time the valves to precisely open and shut in relation to the pistons. When the belt brakes the valves stop moving, that prevents them from opening or closing ultimately preventing combustion (engine stall). When there is no valve movement the engine will not restart, and the engine may sound different when it is cranked over. The sound changes because with no valve movement the engine can not build the compression it needs to ignite the fuel.
Cranking over an engine that has a failed timing belt may cause additional damage and should be avoided. On some engines the valve can occupy the same space that a piston does. The timing belt keeps the piston in time with the valve so they both don’t occupy the same space at the same time. When the belt fails, it may be possible for the piston and valve to collide in that shared space. Additional damage is common on foreign cars and should be checked before repairs are started.