# What does a timing belt do? ## Quick answer A timing belt is a toothed rubber belt that keeps the engine's crankshaft and camshafts turning in sync. ## What is Timing belt? Inside the engine, the pistons move up and down and the valves open and close. The timing belt links the crankshaft to the camshafts so the valves open at exactly the right moment. It is usually hidden behind covers at the front or side of the engine. The camshafts turn at half the speed of the crankshaft, and the belt's teeth keep that ratio exact. Timing belts are made of rubber reinforced with strong cords, and they are guided by idler pulleys and kept tight by a tensioner. On many engines the belt also turns the water pump, so a leaking pump can soak the belt and shorten its life. Because of that, shops often replace the pump, tensioner and pulleys along with the belt. Timing belts wear out and must be replaced on a schedule, often between 60,000 and 100,000 miles, and many makers also list a time limit of several years. Check your owner's manual. If the belt breaks, the engine stops, and on many engines the valves can hit the pistons and cause major damage. These are called interference engines. Many engines use a metal timing chain instead. Chains are designed to last much longer, but they can stretch or rattle if oil changes are skipped. A few engines use a belt that runs in oil, which has its own inspection and replacement needs. ## How it works 1. The crankshaft turns as the pistons move. 2. Teeth on the belt grip gears on the crankshaft and camshafts so they turn together. 3. The camshafts open and close the valves in time with the pistons. 4. A tensioner keeps the belt tight, and on many engines the belt also drives the water pump. ## Types of Timing belt | Type | What it is | | --- | --- | | Timing belt | A toothed rubber belt behind covers that keeps the crankshaft and camshafts in sync; replaced on a schedule. | | Timing chain | A metal chain lubricated by engine oil; usually has no set interval but can stretch with poor maintenance. | | Tensioner and idlers | The tensioner keeps belt tension correct, and idler pulleys guide the belt; both are usually replaced with it. | | Wet belt | A belt designed to run in engine oil on some newer engines; it needs the correct oil and periodic inspection. | ## Common Timing belt problems - A belt past its mileage or age limit, even if it looks fine from the outside. - Oil or coolant leaking onto the belt from a seal or water pump. - Cracked, glazed or missing teeth found during an inspection. - A ticking or whining noise from the timing cover, often from a worn tensioner or idler pulley. - A belt that has broken or jumped teeth, causing the engine to stop or run very poorly. ## Frequently asked questions ### What is the difference between a timing belt and a serpentine belt? A timing belt is inside the engine covers and keeps the engine's internal parts in sync. A serpentine belt is on the outside of the engine and drives accessories such as the alternator and AC compressor. A broken timing belt stops the engine and can damage it. ### How do I know if my car has a timing belt or chain? Your owner's manual or maintenance schedule will say. If it lists a timing belt replacement interval, the engine has a belt. A mechanic can also tell quickly, and many engine specification sheets list it. Many newer cars use timing chains, which usually have no set interval. ### What happens if a timing belt breaks while driving? The engine shuts off and will not restart. On an interference engine, the valves can also hit the pistons and cause expensive damage, sometimes costing more than the car is worth. Steer to a safe place, because you may also lose power steering assist and brake boost. ### How often should a timing belt be replaced? Many timing belts are replaced every 60,000 to 100,000 miles, and many makers also give a time limit of several years, whichever comes first. The exact interval depends on the engine, so check your owner's manual. Severe use, such as towing, may call for sooner replacement. ### How much does timing belt replacement cost? At an independent shop, timing belt replacement often costs about $500 to $1,300, and dealers often charge $800 to $1,800. Many quotes include the tensioner, idler pulleys and water pump. V6 engines and cramped engine bays usually cost more. It is still far cheaper than repairing an engine damaged by a broken belt. ### What is an interference engine? In an interference engine, the valves and pistons use some of the same space at different times. If the timing belt breaks, they can collide and bend valves or damage pistons. In a non-interference engine, a broken belt stops the engine but usually causes no internal damage. ### Are there signs a timing belt is about to fail? Often there are none, which is why the schedule matters. Sometimes there is a ticking or whining noise from the timing cover, oil leaks near it, or visible cracks if the belt is inspected. Do not wait for symptoms on an overdue belt. ### Should I replace the water pump with the timing belt? Often yes, if the belt drives the water pump. Most of the labor to reach the pump is already done, so replacing it at the same time costs little extra. A pump that leaks later could ruin the new belt and mean paying the labor again. ### Do timing chains need replacing? Usually not on a schedule. Timing chains are lubricated by engine oil and often last the life of the engine. Skipped oil changes can wear the chain, guides and tensioner, causing rattling at startup and timing codes such as P0016. Repairs are then often costly. ### Can I drive with an overdue timing belt? You can, but every mile adds risk. The belt can break without warning, and on an interference engine that can mean major engine damage. If you are past the interval or do not know the history of a used car, schedule a replacement soon. ## Sources - [Car Care Council: Car care guide](https://www.carcare.org/car-care-guide/) ## Related terms - [Serpentine belt](https://diagxcar.com/glossary/serpentine-belt) - [Misfire](https://diagxcar.com/glossary/misfire) - [Torque](https://diagxcar.com/glossary/torque) ## Related pages - [How long does a timing belt last?](https://diagxcar.com/how-long/timing-belt): 60,000-100,000 miles - [Timing belt replacement cost](https://diagxcar.com/cost/timing-belt-replacement): $500-$1,300 - [Timing chain replacement cost](https://diagxcar.com/cost/timing-chain-replacement): $1,200-$3,500 - [Why does my car crank but not start?](https://diagxcar.com/symptoms/car-cranks-but-wont-start) --- Source page: https://diagxcar.com/glossary/timing-belt Updated: 2026-11-03 General information, not a substitute for a qualified mechanic.