Mechanical Belt Tensioner, Aftermarket - B46TU, B58, B58TU, S58

Mechanical Belt Tensioner Assembly used on B46TU, B58, B58TU, and S58 engines.

Fitment Notes: 
- F48 X1 28i - Only for 2020-2022 model years (cars produced before 1/31/2022) 
- F39 X2 28i/M35i - Only for 2020-2022 model years (cars produced before 1/31/2022) 
- G05 X5 40i - Only for 2019-2002 model years

The mechanical tensioner works by using a spring that applies and maintains pressure on the belt. Once the spring gets old and tired, it will cause a loose belt. Loose belts are bad because they lead to insufficient alternator charging and poor cooling performance from the water pump. Eventually that loose belt will slip off the pulleys shred itself from aggressive wear.

As a preventative maintenance plan, we recommend replacing the tensioner at every belt change, or 40-60,000 miles. The extent of damage from a failed belt is worth the extra cost every few years.

This complete tensioner includes the roller pulley.

Supersedes BMW part number 11288570439 (11-28-8-570-439).

This part is manufactured by an aftermarket supplier of European auto parts, including many engine components. While not carrying OEM status, this part follows the design of the original very closely and uses similar materials. An aftermarket part may even have the same TUV approval as its OEM counterpart. The brand may even be OEM to another manufacturer besides BMW. This aftermarket brand has a two year warranty - the same as Genuine BMW and OEM brands.