The Castair P3B838SK is a 3-groove (3B) motor pulley with SK taper-lock hub and 8.38" outer diameter. It is the largest 3B SK-hub motor pulley in the Cast Air lineup, designed for compressor systems where three matched B-section belts are required and a larger motor pulley OD is needed to achieve the correct pump drive ratio. The SK hub accepts a range of standard SK bushings, so this pulley can be installed on motors with different shaft diameters by selecting the appropriate bushing.
Note: Cast Air did not provide a dedicated manufacturer product page for this pulley. Specifications are drawn from the product listing and standard 3B SK-hub pulley conventions. Call us before ordering to confirm the correct SK bushing and belt combination for your specific application.
The Largest 3B SK Motor Pulley in the Cast Air Lineup
At 8.38" OD, the P3B838SK drives the pump faster than the 6.15" (P3B615SD) and 7.75" (P3B775SK) options for any given motor RPM. Paired with a 14" pump flywheel, this pulley produces a drive ratio of approximately 1.67:1 — meaning a 1,750 RPM motor drives the pump at about 1,048 RPM. This is within the upper normal range for Cast Air two-stage and heavy-duty single-stage pump designs. The three-groove configuration handles the drive torque that a larger motor pulley OD places on the belt drive system at higher pump speeds.
Pulley Specification Details
- Groove Profile: 3B (three B-section V-belt grooves)
- Hub Type: SK taper-lock (bushing required, sold separately)
- Outer Diameter (OD): 8.38"
- Application: Motor-side pulley for heavy-duty belt-drive air compressors
- Compatibility: Cast Air belt-drive compressors using 3B SK-hub motor pulleys and B-section belts
- Part Number: P3B838SK
Why This Pulley Requires Three Grooves
Larger OD motor pulleys drive the pump faster, which increases both the CFM output and the power demand on the drive system. At 8.38" OD, the belt tension required to transmit the motor's torque without slipping exceeds what two B-section belts can reliably handle at the compressor's duty cycle. Three belts distribute the load — each belt carries less tension, runs cooler, and lasts longer. The pump flywheel must also be 3-groove for this to work. If your existing flywheel is 2-groove, the pulley and flywheel must be changed together.
SK Taper-Lock Hub — Installation and Bushing Selection
- The SK hub requires a standard SK bushing bored to your motor shaft diameter
- Common SK bushing bore sizes: 5/8", 7/8", 1", 1-1/8", 1-3/8", 1-5/8", 1-7/8" — specify your shaft diameter when ordering
- Installation: slide bushing on shaft, align key, hand-thread mounting screws through pulley into bushing flange, torque evenly
- Removal: back screws out, thread into jack holes to push the taper apart
- The SK bushing can often be reused when the motor is replaced, making this a long-service-life pulley assembly
When Does a Shop Need the P3B838SK?
- Original 8.38" 3B SK-hub motor pulley is worn, cracked, or groove-damaged from belt failure
- Rebuilding a heavy-duty Cast Air compressor to original drive specifications
- Motor replacement on a 3-groove drive system where the pulley is in good condition but the bushing bore needs to change for a different shaft size
- Pump is running at confirmed low RPM (tachometer) and the motor pulley is identified as undersized for the application
Cast Air 3B Motor Pulley Comparison
- P3B615SD — 6.15" OD — $105.88 — SD hub, smaller OD, lower pump RPM
- P3B775SK — 7.75" OD — SK hub, mid-range OD
- P3B838SK — 8.38" OD — $132.83 (this unit) — SK hub, largest in the 3B series, highest pump RPM
Technical Specifications
- Part Number: P3B838SK
- Manufacturer: Cast Air (Castair)
- Groove Type: 3B (three B-section V-belt grooves)
- Hub Type: SK taper-lock (bushing sold separately)
- Outer Diameter: 8.38"
- Belt Section: B-section (three matched belts)
- Price: $132.83
- Manufacturer Data: Product page not available — specifications from product listing data
What Is Included
- 1x Castair P3B838SK motor pulley (SK hub)
SK bushing and three B-section matched belts are not included. Call us with your motor shaft diameter and drive center distance and we will help you source the complete assembly.
Why Buy From Air Compressor Factory Direct?
Heavy-duty 3-groove SK-hub drive systems involve specific components — and ordering the wrong bushing bore or belt length means the compressor does not run right. We have been selling Cast Air parts since 2016 and know the product lineup well enough to help you avoid those mistakes. 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 identify the correct SK bushing for your shaft
- Full manufacturer warranty
- Complete drive system sourcing — we help you order the full replacement kit
Call 866-217-0063 for quick answers and help!
