The Castair P2B675-13/8 is a 2-groove (2B) replacement motor pulley with a fixed 1-3/8" bore and 6.75" outer diameter, designed for Cast Air belt-drive air compressor systems. This is the direct replacement when your original motor pulley shows groove wear, cracking, or physical damage from a thrown belt — and the motor shaft is 1-3/8".
Note: Cast Air did not provide a dedicated manufacturer product page for this pulley. Specifications are drawn from the product listing and standard 2B-groove pulley engineering conventions. Contact us to confirm fitment for your specific application.
Understanding the 2B Motor Pulley
The 2B designation means two B-section V-belt grooves. B-section is the standard for compressor motor drives in the fractional to 5 HP range. Running two matched B-section belts instead of one distributes load across both groove surfaces, reduces belt slip during startup under load, and extends belt life — all of which matters in a shop where the compressor runs continuously. The 6.75" OD determines your belt drive ratio; paired with the flywheel pulley on your Cast Air pump, it sets the pump RPM and therefore your delivered CFM.
Pulley Specification Details
- Groove Profile: 2B (two B-section V-belt grooves)
- Bore Type: Fixed bore — 1-3/8" (1.375") shaft diameter
- Outer Diameter (OD): 6.75"
- Application: Motor-side pulley for belt-drive air compressors
- Compatibility: Castair belt-drive compressor systems with 1-3/8" motor shafts and B-section belts
- Part Number: P2B675-13/8
Drive Ratio and Pump Speed — Why OD Matters
Motor pulley OD and pump flywheel OD define your pump RPM. At 1,750 RPM motor speed, a 6.75" motor pulley paired with a 14" flywheel on the pump produces roughly 844 pump RPM — within the correct operating range for most Cast Air single-stage pump designs. Installing the wrong OD shifts the ratio, over-speeding the pump (wear, heat) or under-speeding it (CFM loss). Always verify the OD matches the original before ordering a replacement.
Fixed Bore vs. Taper-Lock Pulley Selection
- Fixed bore pulleys (like the P2B675-13/8) are machined for a specific shaft diameter and mount with a keyway and set screw. Correct for a direct swap when the original was also a fixed bore 1-3/8" unit.
- Taper-lock (SK/SD hub) pulleys use interchangeable bushings adapting to different shaft sizes. Better for installations where the motor may be replaced later, but not a direct swap for fixed-bore pulleys.
- If the original pulley was fixed bore 1-3/8" and the OD was 6.75", the P2B675-13/8 installs as a direct replacement with no adapters or modifications.
When Does a Shop Need This Pulley?
- Existing motor pulley shows cracked grooves, chipped flanges, or V-belt contact wear causing belt slip or belt throw
- Motor swap resulted in a 1-3/8" shaft — this pulley maintains the original drive ratio
- Rebuilding a Cast Air belt-drive compressor to OEM specification
- Compressor pump RPM is measurably off (tachometer) and pulley OD has been identified as the cause
2B Fixed-Bore 1-3/8" Motor Pulley Size Comparison
- P2B625-13/8 — 6.25" OD — $68.34 — smallest in the series; lower pump RPM for the same motor speed
- P2B675-13/8 — 6.75" OD — $71.23 (this unit) — mid-range OD, common on Cast Air mid-HP single-stage compressors
- P2B80-13/8 — 8.0" OD — $88.55 — larger diameter increases pump RPM; higher CFM on appropriate pump models
- P2B875-13/8 — 8.75" OD — $103.95 — largest fixed-bore option in the 1-3/8" bore lineup
Measure your original pulley OD before ordering. If you are not sure which size your compressor uses, call us and we will identify the correct replacement for your Cast Air model.
Technical Specifications
- Part Number: P2B675-13/8
- Manufacturer: Cast Air (Castair)
- Groove Type: 2B (two B-section V-belt grooves)
- Bore: Fixed, 1-3/8" (1.375")
- Outer Diameter: 6.75"
- Bore Style: Fixed (keyway and set screw)
- Belt Section: B-section (two matched belts)
- Price: $71.23
- Manufacturer Data: Product page not available — specifications from product listing data
What Is Included
- 1x Castair P2B675-13/8 motor pulley
- Set screw(s) for shaft retention
B-section matched belts are not included. Order separately based on your drive center distance.
Why Buy From Air Compressor Factory Direct?
We have been sourcing and selling Cast Air compressor parts since 2016. We stock the motor pulley lineup across OD sizes so you get the right part without guessing. Free shipping on every order. Our tech support team can confirm fitment for your specific Cast Air model before you place your order — no automated call centers, just people who know compressor drive systems.
- Cast Air specialist since 2016
- Free shipping on every order
- Free tech support — call to confirm fitment before ordering
- Full manufacturer warranty on all parts
- Honest parts guidance — we will steer you to the correct OD for your application
Call 866-217-0063 for quick answers and help!
