BMW 525i Timing Belt Tensioner Replacement Cost

The timing belt tensioner, as the name implies, provides tension to the timing belt to ensure total contact between the teeth on the belt and the teeth on the camshaft and crankshaft timing gears. With the appropriate amount of tension from the belt tensioner, the belt and gears will remain aligned so the engine remains properly timed.

As the timing belt is installed this timing belt tensioner pulley is tightened to manufacturer specifications, and that places the proper amount of tension on the belt. It is bolted through the center into the engine, and the smooth side of the timing belt rests tightly against the pulley as it constantly rotates.

If the timing belt tensioner fails, there will be a very audible chirping noise from the front of the engine. This is because the tensioner bearing is no longer smooth. If it is not changed immediately, the engine will being running roughly, or stall completely. As a worst-case scenario, internal engine damage may occur due to slippage or breakage of the timing belt. The check engine light will illuminate on the dashboard in the event of total failure, and OBD trouble codes for misfires, crankshaft position, and camshaft position will be stored.

It is not recommended to drive a vehicle suspected of timing component damage. If the vehicle will run at all, it can quickly result in complete engine failure as described above.

Timing belt tensioner pulleys are replaced during a timing belt replacement service, either as preventive maintenance, or due to suspected failure. This means the average timing belt tensioner replacement occurs between 60,000 and 105,000 miles, depending on the manufacturer specified timing belt service interval.

Diagnosis of a failed or failing tensioner requires removal of many components, and hands on inspection of the timing belt tensioner. If the servicing technician finds the pulley is loose or damaged in any way, they will recommend immediate replacement of, at minimum, the timing belt and timing belt tensioner pulley.

At a minimum, replacement involves removal of the timing cover, timing belt tensioner, timing belt, and the timing belt pulley. The timing belt tensioner is typically attached by one bolt, but installation requires the proper amount of tension to be applied to the timing belt, and idler pulley retaining bolt. Once all components are replaced, the timing components can be installed onto the engine, and the engine will be tested for proper operation and timing before additional components are replaced.

Since this service requires removal of the timing belt, it is recommended to replace the timing belt, water pump, and possibly front seals at the same time, unless they have been recently serviced. This is much more cost effective than returning for the same service after a partial service interval has elapsed.

It may be necessary for the motor mounts to be removed from the vehicle, as well as engine cooling fans, the radiator, and all engine accessories. This may include components like the alternator, A/C compressor, mounting brackets, coolant or fuel lines, and any other component that interfere with access to the timing belt cover.

Since timing belt tensioner replacement necessitates the removal of timing components, it is not recommended for the DIYer to attempt this task. A thorough knowledge of internal engine components, engine timing, additional systems, and several specialty tools are required to properly perform this repair.