How to Perform Timing Belt Replacement Service

What is a timing belt and how does it function?

A car engine timing belt is a fiber reinforced, toothed drive belt manufactured with the use of durable compounds such as highly saturated nitrile. The timing belt permits the crankshaft to drive the camshafts in the cylinder head at half the RPMs of the crankshaft. The camshafts then open and close the engine’s intake and exhaust valves in time together with the movement and position of the pistons in the engine

When to Change the timing belt?

  • Every 60k-90k miles.If an engine has a timing belt, the timing belt must be changed at the service interval specified by the  car manufacturer regardless of whether or not any issue is visible, typically in the range of 60,000 to 90,000 miles. Your car owner’s manual should mention the specific service interval.
  • Engine stops abruptly or will not start.Periodically, timing belts can break, or skip, while the engine is running.
  • Rough engine operation.The molded, reinforced teeth on the timing belt engage gears on the crankshaft and camshafts. After many tens of thousands of miles, the teeth can wear or break, or the belt can stretch, thus making the belt to jump position on the crankshaft or camshaft gears. Should the belt jump, the engine will run poorly and perhaps not at all.
  • Banging or clanking engine noise.On some car engines, if the timing belt has jumped, the pistons and valves can collide and there will be noise and damage. These engine designs are termed as interference engines. If your vehicle has an interference engine, changing the timing belt according to the maintenance schedule will minimize the chance that a belt failure will create engine damage.

How do mechanics Change the timing belt?

Engine designs differ, and thus the replacement procedure will vary, but broadly, the procedure is as follows:

  • Disconnect the battery ground cable.
  • Once the engine is seen to be cold, set the crankshaft to top dead center with the number one piston on the compression stroke. Take out the crankshaft pulley.
  • Remove all accessories interfering with the removal of the timing belt covers.
  • Remove timing belt covers. Lock camshafts, as needed, and note position of camshaft timing marks. Remove timing belt tensioner and idler pulleys. Remove timing belt.
  • If replacing the water pump, do so at this time, and of course drain the cooling system first. If the engine cooling system thermostat is only accessible with water pump replacement, the thermostat should be changed as well.
  • Installation of the new timing belt includes all of the above steps, performed in reverse, following strict guidelines to assure camshaft and crankshaft (and balancing shaft, if equipped) are in perfect alignment after tensioner has been set.
  • Upon completion of the installation, the engine crankshaft is turned by hand 720 degrees and the correct position of the timing marks on the crankshaft and the camshafts is ascertained.
  • The car is road tested to confirm normal operation and a service sticker is affixed to the engine noting the date of belt replacement and the car mileage.

Is it safe to drive with a timing belt issue?

No, because if a worn out timing belt to snap while underway, perhaps on a highway, it could create a risk of complete loss of engine power while surrounded by fast moving cars. Once your car has reached the recommended replacement mileage for the belt, you can eliminate the risk of sudden and unexpected timing belt breakage by having it changed. If your engine is of the interference type, it is especially vital to replace the belt according to the maintenance schedule because sudden breakage of the timing belt, while the engine is running, will likely cause great damage to internal engine components the likes of valves and pistons.

When changing the timing belt keep in mind:

  • An interference engine should be carefully checked before a broken timing belt is changed because it may have sustained damage that will have to be repaired prior to mounting a new belt.
  • The timing belt system includes idler pulleys and a belt tensioner. These parts should be replaced along with the belt.
  • On some vehicles, the timing belt drives the engine’s water pump. Mechanics will often recommend changing the water pump at the same time that the timing belt is changed.


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