Castair SD158 — Replacement Motor SD Hub, 1-5/8" Shaft
The Castair SD158 is a replacement SD-series motor hub for 1-5/8-inch motor output shafts used in Cast Air belt-driven compressor installations. This is the larger SD hub — the 1-5/8-inch shaft diameter is typically found on motors in the 5 HP and above range where the motor's output shaft steps up from the 1-3/8-inch size used on smaller compressors. When the motor hub fails on these larger-shaft applications, the SD158 is the correct replacement.
The SD designation identifies the hub series — SD hubs are used on specific Cast Air compressor models and are not interchangeable with SK-series hubs. If you are not certain whether your compressor uses an SD or SK hub, look at the existing hub for a part number stamp, or call us with your compressor model number and we will confirm the correct part 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 transfers power to the compressor pump via V-belt. On startup, the hub takes the full torque spike of the motor coming up to speed under load. Over extended service, the bore can wear out of round, keyways can enlarge, or the hub body can fatigue and crack. Any of these conditions lead to vibration, belt slippage, and alignment problems that cannot be corrected by belt tension alone. The solution is a direct hub replacement with the correct OEM part.
Key Features
- Shaft Size: 1-5/8 inch: Machines to fit motor output shafts measuring 1.625 inches in diameter — measure your shaft with a caliper before ordering
- SD Series Hub: Matched to Cast Air SD-series hub applications — verify your compressor uses SD-series hubs before ordering (see note below on SD vs. SK)
- OEM Cast Air Part: Manufactured to Cast Air specifications for correct bore tolerance and fit
- Precision Machined Bore: Correct tolerance prevents shaft slop that causes pulley runout and misalignment
- Belt-Drive Application: Designed for belt-driven Cast Air compressor configurations where motor-to-pump power transfer is via sheave and V-belt
Technical Specifications
- Part Number: SD158
- Shaft Diameter: 1-5/8 inch (1.625")
- Hub Series: SD
- Component Type: Replacement motor drive hub
- Manufacturer: Cast Air (Castair)
- Price: $31.57
SD and SK Hub Series — Know Which You Need
Cast Air uses two hub series — SD and SK — on different compressor configurations. They are not interchangeable. Check your existing hub for a part number, or call us with your compressor model to confirm.
- SD138 — SD series, 1-3/8" shaft ($31.57)
- SD158 — SD series, 1-5/8" shaft ($31.57). This product.
- SK158 — SK series, 1-5/8" shaft ($52.36)
- SK178 — SK series, 1-7/8" shaft ($52.36)
When Does a Shop Need the SD158
Replace the motor hub when:
- The existing hub on a larger-shaft Cast Air compressor shows cracking, bore wear, or visible keyway damage
- The compressor vibrates unusually at startup or during operation — often caused by a hub that has gone loose on the shaft
- Belt alignment problems persist despite correct tension and sheave alignment — indicating hub bore runout
- Installing a replacement motor with a 1-5/8-inch output shaft on an SD-series compressor configuration
- Preventive maintenance — stocking the correct hub before the original fails
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 — confirm SD vs. SK series and correct shaft size before ordering
- Full manufacturer warranty
Call 866-217-0063 for quick answers and help!
