How to Change a Timing Belt: Signs, Intervals, and the Full Procedure

A timing belt is one of the most critical components in an engine. It synchronises the rotation of the crankshaft and camshaft so that the valves open and close at exactly the right moment during each engine cycle. When a timing belt fails, the consequences can range from a stalled engine to catastrophic internal damage costing thousands of dollars.

This guide explains how timing belts work, when they need replacing, and what the replacement process involves.

Timing Belt vs. Timing Chain

Not all engines use a timing belt. Many modern engines use a timing chain instead, which is a metal chain similar to a bicycle chain. Timing chains are designed to last the life of the engine in most cases, while timing belts are a scheduled replacement item. Check your workshop manual or owner’s manual to confirm whether your engine uses a belt or chain. If it has a belt, it will have a replacement interval listed in the service schedule.

When to Replace the Timing Belt

Timing belt replacement intervals vary by manufacturer but typically fall between 60,000 km and 150,000 km, or every 5 to 10 years (whichever comes first). Some common examples:

• Toyota (many models): 150,000 km or 10 years
• Nissan (many models): 100,000 km or 7 years
• Subaru (EJ series engines): 105,000 km
• Mitsubishi (4G63/4G64): 100,000 km
• Honda (J-series V6): 168,000 km or 7 years

Always check your specific vehicle’s workshop manual for the exact interval, as it varies between engine variants within the same brand.

Interference vs. Non-Interference Engines

This is the most important concept to understand about timing belts. In an interference engine, the valves and pistons occupy the same space in the cylinder at different times. If the timing belt breaks, the pistons will hit the open valves, bending them and potentially damaging the pistons, cylinder head, and other components. This turns a $500 belt job into a $3,000 to $5,000 engine repair.

In a non-interference engine, the valves and pistons have enough clearance that a broken belt will not cause contact. The engine will simply stop running and can be repaired by fitting a new belt.

Most modern engines are interference designs. Your workshop manual will confirm which type your engine is, and this is a key reason not to exceed the recommended replacement interval.

Signs of a Worn Timing Belt

• High-pitched squealing from the front of the engine that changes with engine speed (not to be confused with accessory belt noise)
• Engine misfires or rough running caused by the belt skipping a tooth, which throws off valve timing
• Visible cracking or glazing on the belt surface if you can see it through an inspection cover
• Oil leaks near the timing cover that may indicate a failing timing belt seal
• Engine will not start after the belt has fully broken

In most cases, a timing belt gives little or no warning before failure. This is why replacement by mileage/age interval is essential rather than waiting for symptoms.

What Gets Replaced During a Timing Belt Job

A timing belt replacement should always include the following components, since they are accessed during the job and have similar service lives:

• Timing belt (obviously)
• Tensioner pulley and hydraulic tensioner (the spring-loaded mechanism that keeps the belt tight)
• Idler pulleys (smooth pulleys that guide the belt path)
• Water pump (on most engines, the water pump is driven by the timing belt and should be replaced at the same time since it is behind the same covers)
• Front crankshaft and camshaft seals (oil seals that are exposed during the job)

Replacing all these items together is standard practice because the labour to access them is the bulk of the cost. Skipping the water pump or tensioner and having one fail 20,000 km later means doing the entire job again.

Overview of the Replacement Procedure

A timing belt replacement is an intermediate to advanced job. The general steps are:

1. Remove accessories. This typically includes the drive belts, alternator, power steering pump, and sometimes the radiator to gain access to the timing covers.
2. Remove the timing covers. These are the plastic or metal covers on the front of the engine that protect the belt.
3. Set the engine to Top Dead Centre (TDC). Rotate the crankshaft until the timing marks on the crankshaft pulley and camshaft sprocket(s) align with the reference marks on the engine. These marks are specific to each engine and are detailed in the workshop manual with diagrams.
4. Release the tensioner and remove the old belt. Note the belt routing before removal, or refer to the routing diagram in your manual.
5. Replace the tensioner, idler pulleys, water pump, and seals.
6. Install the new belt. Route it according to the diagram, making sure all timing marks remain aligned. This is the most critical step. Being off by even one tooth will cause poor running or engine damage.
7. Set the tensioner. Follow the manual’s tensioner setting procedure, which often involves a specific sequence of releasing a pin, turning the crankshaft two full revolutions, and then checking that all marks still align.
8. Reassemble. Refit the timing covers, accessories, and drive belts. Refill the cooling system if the water pump was replaced.

Why You Need the Workshop Manual for This Job

Timing belt replacement is one of the jobs where having the correct workshop manual is not optional. The timing mark locations, belt routing, tensioner procedures, and torque specifications are completely different between engine types. Even two engines from the same manufacturer (like Toyota’s 2AZ-FE and 1GR-FE) have entirely different timing setups.

MechanicMate carries workshop manuals with complete timing belt procedures for Toyota, Nissan, Subaru, Mitsubishi, Honda, and many more. Each manual includes timing mark diagrams, belt routing illustrations, tensioner specifications, and torque values for your exact engine. Find yours at mechanicmate.net/shop.