Belt Idler Pulley – 11 28 8 673 720 (INA)

Description

The 11 28 8 673 720 Accessory Belt Idler Pulley by INA (Schaeffler) is an OEM-quality deflection pulley for BMW N55 TwinPower Turbo and S55 Twin Turbo engines found across the F-series chassis lineup. Also known as a deflection roller, this pulley mounts separately from the belt tensioner and guides the v-ribbed accessory belt around the drive path — keeping the belt properly seated and aligned as it powers the alternator, A/C compressor, and power steering pump (where equipped).

Because this pulley spins continuously at engine speed, it endures constant load, heat, and engine bay vibration. Over time, the sealed bearing wears and the plastic pulley body begins to deteriorate. As the bearing degrades, it produces a distinct screeching or rumbling noise, and it develops resistance when spun by hand. Furthermore, BMW N55 idler pulleys carry a known risk of plastic body cracking or shattering — a failure mode that can fling debris into the radiator, cooling hoses, and other critical engine bay components, turning a simple pulley replacement into a much more costly repair. Consequently, replacing this pulley proactively at every belt service interval is strongly recommended. Installing this 11 28 8 673 720 from INA restores quiet, stable belt tracking and eliminates that failure risk entirely.

11 28 8 673 720 — INA (Schaeffler) OEM Supply

INA, a brand within the Schaeffler Group, is one of BMW’s primary OEM suppliers for belt drive components — including tensioners, idler pulleys, and bearing assemblies across multiple engine families. Because INA manufactures this 11 28 8 673 720 to the exact specifications BMW established for the N55 and S55 engine accessory drives, it delivers the same fit, geometry, and bearing quality as the original factory part. In addition, the INA sealed bearing resists the heat and vibration of the turbocharged engine environment, and the pulley body meets OEM dimensional tolerances for correct belt clearances and alignment — making it the most direct-fit replacement available.

Signs Your Idler Pulley Needs Replacing

Catching idler pulley failure early prevents accessory belt loss and downstream damage. Watch for these warning signs:

• Screeching, chirping, or rumbling noise from the front of the engine that changes with RPM

• Resistance, roughness, or grinding when spinning the pulley by hand with the engine off

• Visible cracks, chips, or stress marks on the plastic pulley body

• Belt flutter or vibration during acceleration or at idle

• Accelerated or uneven wear across the width of the accessory belt

If any of these indicators appear, replace the idler pulley promptly. Given the plastic body failure risk on these pulleys, do not delay.

Key Features

• OEM Reference: 11 28 8 673 720

• Brand: INA (Schaeffler) — BMW OEM supplier for belt drive components

• Precision sealed bearing for smooth, quiet rotation under continuous engine load

• OEM-spec pulley geometry for correct belt contact, clearance, and lateral alignment

• Engineered to N55/S55 specifications for correct accessory drive geometry

• Direct-fit replacement — no modifications required

• Eliminates the plastic body cracking/shattering failure risk associated with worn pulleys

• Helps prevent belt flutter, noise, and premature accessory belt wear

Service Notes

• First, replace this idler pulley together with the accessory belt and belt tensioner — since all three components wear at the same pace, replacing them as a set at every belt service interval prevents repeat labor and eliminates comeback risk

• Next, spin all accessory drive pulleys by hand with the engine off and listen for grinding, rumbling, or resistance — any roughness confirms bearing wear and warrants replacement

• Also inspect the plastic pulley body carefully for cracks, chips, or stress fractures before reusing any existing pulley; a cracked pulley should be replaced immediately regardless of bearing condition

• Finally, verify correct belt routing and confirm the belt seats fully in all pulley grooves before starting the engine

11 28 8 673 720 Idler Pulley — Compatibility & Applications

Always verify fitment by VIN before ordering. Multiple variants may exist within the same model year.

Cross Reference Numbers

• 11 28 8 673 720 (BMW OEM — current)

• 11 28 7 589 361 / 11 28 8 604 267 (BMW OEM — superseded)

• INA / Schaeffler 532 0660 10

• Gates T36728

Additional information