Upper Deflection Pulley, OEM - F87 M2 S55, F80 M3, G80 M3, F82 M4, G82 M4, X3M/X4M
OEM idler pulley to keep your belt running quiet and true
The S55/S58 deflection, or idler, pulley is located separate from the tensioner pulley and guides the belt around other accessories.
The pulley contains a set of bearings, that when worn, will produce a screeching or rumbling sound. It's important to inspect and replace the pulley regularly. Spin the pulley by hand and listen for grinding or rumbling sounds and if there is resistance. All of these are signs of bad bearings. The pulley wheel is made of plastic and they are known to crack and snap and get flung around the engine compartment. They can damage your radiator, hoses, fan, and other critical items that will lead to a more expansive/expensive repair. Since the deflection pulley is bolted in place, not pressed on, it is easily replaced during a routine belt change.
This pulley is manufactured by INA, the original supplier to BMW for this part and other pulleys. Since it is an OEM part, it conforms to the original design that BMW specified for the engines listed above. It comes with a two year warranty.
F87 (2016+) > M2 Competition S55 (2019+)
F80 (2015-2018) > M3 (2015-2018)
G80 (2021-) > M3 (2021-)
F82 / F83 (2015-2020) > M4 (2015-2020)
G82 / G83 (2021-) > M4 (2021-)
F97 X3M (2020+) > X3M
F98 X4M (2020+) > X4M