A timing belt is a toothed rubber belt that keeps the camshafts turning in step with the crankshaft so the valves open at the right time. Unlike a timing chain, it wears out and must be replaced on a schedule, commonly somewhere between 60,000 and 105,000 miles or after a set number of years, whichever comes first. On an interference engine, a broken timing belt lets the pistons hit the valves, which can turn a scheduled maintenance job into an engine replacement.
When to replace a timing belt
- At the manufacturer interval in your maintenance schedule, by mileage or by age; rubber deteriorates even on low-mileage vehicles.
- When it is contaminated by oil or coolant from a leaking seal or water pump.
- When buying a used vehicle with no record of the last belt change.
Timing belt symptoms
Timing belts often give little warning before they fail. Signs worth acting on:
- Cracks, glazing, missing teeth or frayed edges when the belt cover is removed
- Whining or ticking from a worn tensioner or idler pulley
- Oil on the belt from a leaking cam or crank seal; see oil leaks
- Cam and crank correlation codes such as P0016 after a belt has jumped a tooth
- An engine that cranks unusually fast and will not start, which can mean the belt has broken; see car won’t start
Interference vs non-interference engines
| Engine type | If the belt breaks |
|---|---|
| Interference | Pistons can strike open valves: bent valves and possibly damaged pistons and heads |
| Non-interference | The engine stops; usually no internal damage, and a new belt gets it running |
Many modern engines are interference designs because tighter clearances improve efficiency. Check your engine before assuming a broken belt is harmless.
What to replace with the timing belt
Most of the cost is labor to reach the belt, so the tensioner, idler pulleys and often the water pump (when the belt drives it) and the cam and crank seals are usually replaced at the same time. Set the timing marks carefully, rotate the engine by hand two full turns and recheck the marks before starting it.
Which engines use timing belts?
Many four-cylinder and V6 engines use belts. Most modern V8s, including the GM LS family and Ford Coyote, use timing chains, and the Cummins diesels use gears; see timing chain vs timing belt. Subaru EJ-series engines use timing belts, while the newer FA and FB engines switched to chains; see EJ255 vs EJ257 and FA20 vs FA24.
A belt broke: repair or replace?
After a belt failure on an interference engine, a compression or leak-down test shows whether valves are bent. Bent valves mean cylinder head work at minimum, and if pistons are damaged a replacement can cost less; see engine replacement cost and compare engines by code, including Subaru short blocks, on our engines page.
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