The Castair P2B875-13/8 is the largest 2-groove (2B) fixed-bore motor pulley in the Cast Air 1-3/8" bore lineup, with an 8.75" outer diameter. This pulley is used where the application requires the highest pump RPM available from the 2B fixed-bore series — typically on Cast Air compressors with larger single-stage pump designs where the motor is sized to sustain the increased load. If your original 8.75" motor pulley is worn or damaged, this is the direct OEM-spec replacement.
Note: Cast Air did not provide a dedicated manufacturer product page for this pulley. Specifications are drawn from the product listing and standard 2B pulley engineering conventions. Call us to confirm fitment for your application before ordering.
The 8.75" OD Motor Pulley — What It Means for Pump Speed
An 8.75" motor pulley is the largest in the Cast Air 2B fixed-bore 1-3/8" series. Paired with a 14" flywheel on the pump side, this produces a drive ratio of approximately 1.6:1, driving the pump at about 1,094 RPM from a 1,750 RPM motor. That is at the upper limit of the safe operating range for most Cast Air single-stage pump designs. This pulley should only be used as a replacement for the same OD — do not upsize a motor pulley without verifying the pump and motor are rated for the resulting pump RPM and increased load.
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): 8.75"
- 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: P2B875-13/8
Is This the Right Pulley for Your Application?
The 8.75" OD is not a universal upgrade — it is a specific replacement for compressors that were designed and shipped with this size motor pulley. If your compressor originally had a smaller motor pulley and you are considering upsizing to increase CFM, verify with us first. Running a pump faster than its design RPM accelerates wear on the piston rings, valves, and connecting rod bearings, and can overheat the pump. Use this pulley as a like-for-like replacement, not a performance modification, unless you have confirmed the pump supports it.
Fixed Bore vs. Taper-Lock
- Fixed bore (this pulley): Bored to exactly 1-3/8". Installs on the motor shaft with keyway and set screw. Correct replacement when the original was also fixed bore 1-3/8".
- Taper-lock (SK/SD): Uses a removable bushing. Separate part, different installation — not interchangeable with fixed bore without modification.
- Confirm your motor shaft is exactly 1-3/8" diameter before ordering.
When Does a Shop Need This Pulley?
- Original 8.75" motor pulley is cracked, groove-worn, or damaged from a thrown or broken belt
- Rebuilding a Cast Air compressor that factory-shipped with an 8.75" motor pulley
- Motor was replaced and the new motor has a 1-3/8" shaft — this maintains the original drive ratio
- Pump RPM has dropped (confirmed by tachometer) and the motor pulley 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, lowest pump RPM
- P2B675-13/8 — 6.75" OD — $71.23 — standard mid-range
- P2B725-11/8 — 7.5" OD — $84.70 — larger for higher pump speed requirements
- P2B80-13/8 — 8.0" OD — $88.55 — high-speed option
- P2B875-13/8 — 8.75" OD — $103.95 (this unit) — largest in the fixed-bore 1-3/8" series
Technical Specifications
- Part Number: P2B875-13/8
- Manufacturer: Cast Air (Castair)
- Groove Type: 2B (two B-section V-belt grooves)
- Bore: Fixed, 1-3/8" (1.375")
- Outer Diameter: 8.75"
- Bore Style: Fixed (keyway and set screw)
- Belt Section: B-section (two matched belts)
- Price: $103.95
- Manufacturer Data: Product page not available — specifications from product listing data
What Is Included
- 1x Castair P2B875-13/8 motor pulley
- Set screw(s) for shaft retention
B-section matched belts are not included. Measure your drive center distance to select the correct belt length.
Why Buy From Air Compressor Factory Direct?
We have been selling Cast Air replacement parts since 2016 and carry the complete motor pulley lineup. If you are not sure whether 8.75" is the correct OD for your compressor, call us before ordering — a wrong-size pulley that changes your drive ratio can cause real damage. We confirm fitment before you buy. Free shipping, free tech support, and full manufacturer warranty on all Cast Air parts.
- Cast Air specialist since 2016
- Free shipping on all orders
- Free tech support — we confirm the correct size before you order
- Full manufacturer warranty
- Honest guidance — we will advise against upsizing if the pump is not rated for it
Call 866-217-0063 for quick answers and help!
