Castair SK178 — Replacement Motor SK Hub, 1-7/8" Shaft
The Castair SK178 is a replacement SK-series motor hub for motors with a 1-7/8-inch output shaft — the largest shaft diameter in the Cast Air SK hub range. This hub is used on Cast Air compressor configurations in the upper HP range where the motor output shaft steps up to 1-7/8 inches. If your compressor uses an SK-series hub and the motor shaft measures 1-7/8 inches in diameter, the SK178 is your replacement part. The smaller SK158 (1-5/8") will not fit.
As with all belt-drive motor hubs, confirming the hub series (SK vs. SD) and measuring the shaft diameter accurately are critical before ordering. A hub that is 1/4 inch off in shaft diameter will not seat, and an SK hub on an SD application (or vice versa) is not an acceptable substitute regardless of shaft size. Call us if you are unsure — this is exactly the kind of question we answer before you order.
What the Motor Hub Does
The motor hub mounts to the electric motor's output shaft and carries the drive sheave that transmits torque to the compressor pump via V-belt. On every startup, the hub absorbs the full torque spike of the motor coming up to speed. Over time in continuous commercial service, hub bores wear out of round, keyways enlarge, or the hub body cracks from fatigue and vibration. Any of these failures cause vibration, belt slippage, and misalignment problems. Replacing the hub with the correct OEM part resolves these issues cleanly.
Key Features
- SK Series Hub: For Cast Air compressors specifying SK-series motor hubs — not interchangeable with SD-series hubs used on other configurations
- 1-7/8-Inch Shaft Bore: The largest shaft diameter in the Castair SK hub range — machined precisely for a 1-7/8-inch (1.875") motor output shaft
- OEM Cast Air Replacement: Manufactured to original Cast Air specifications
- Belt-Drive Application: Transmits motor torque to the belt-drive system — sized for higher-HP Cast Air compressor motor configurations
- Direct Replacement: Designed for direct installation on SK-hub compressor configurations without modification
Technical Specifications
- Part Number: SK178
- Hub Series: SK
- Shaft Diameter: 1-7/8 inch (1.875")
- Component Type: Replacement motor drive hub
- Manufacturer: Cast Air (Castair)
- Price: $52.36
Cast Air Motor Hub Lineup — Full Series Reference
- SD138 — SD series, 1-3/8" shaft ($31.57)
- SD158 — SD series, 1-5/8" shaft ($31.57)
- SK158 — SK series, 1-5/8" shaft ($52.36)
- SK178 — SK series, 1-7/8" shaft ($52.36). This product.
When Does a Shop Need the SK178
Replace the motor hub when:
- The SK hub on a larger Cast Air compressor is cracked, the bore is worn, or the keyway is damaged
- The compressor vibrates at startup or during operation — a common symptom of a hub that has loosened on the shaft
- Belt misalignment persists despite correct tension — worn hub bore causing pulley runout
- Installing a replacement motor with a 1-7/8-inch output shaft on an SK-hub compressor configuration
- Preventive maintenance stocking for facilities running Cast Air equipment in the upper HP range
Why Buy From Air Compressor Factory Direct?
- Authorized Cast Air dealer since 2016
- Free shipping on qualifying orders
- Free technical support at 866-217-0063 — we can confirm hub series and shaft size from your compressor model number
- Full manufacturer warranty
Call 866-217-0063 for quick answers and help!
