{"product_id":"castair-replacement-motor-hub-1-3-8-shaft-sd138","title":"Castair Replacement Motor Hub 1-3\/8\" Shaft SD138","description":"\u003ch2\u003eCastair SD138 — Replacement Motor Hub, 1-3\/8\" Shaft\u003c\/h2\u003e\n\n\u003cp\u003eThe Castair SD138 is a replacement motor hub sized for motors with a 1-3\/8-inch output shaft. This is the SD-series drive hub that connects the electric motor shaft to the belt-drive flywheel and pulley system on Cast Air belt-driven compressor units. When the hub cracks, strips, or wears to the point where it no longer holds the drive pulley securely, the correct repair is a direct OEM replacement — not an improvised substitute that is close but not engineered for this application.\u003c\/p\u003e\n\n\u003cp\u003eThe SD138 designation tells you everything: SD series, 138 = 1-3\/8 inches. Measure your motor shaft with a caliper before ordering — 1-3\/8 inches is 1.375 inches in decimal. If your shaft is larger at 1-5\/8 inches, you need the SD158 instead.\u003c\/p\u003e\n\n\u003ch3\u003eWhat the Motor Hub Does\u003c\/h3\u003e\n\u003cp\u003eOn a belt-driven compressor, the motor hub mounts to the motor's output shaft and carries the drive sheave (pulley) that transfers torque to the compressor pump via V-belt. Every time the motor starts, the hub absorbs the full startup torque load. Over time, the keyway can wear, the bore can develop slop, or the hub body can crack from fatigue. Any of these conditions cause belt drive problems: vibration, misalignment, slipping belts, or a compressor that simply will not run correctly. Replacing the hub with the correct OEM part solves all of these symptoms.\u003c\/p\u003e\n\n\u003ch3\u003eKey Features\u003c\/h3\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003eShaft Size: 1-3\/8 inch:\u003c\/strong\u003e Fits motor output shafts measuring 1.375 inches in diameter — the SD138 bore is machined specifically for this shaft size\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eSD Series Hub:\u003c\/strong\u003e The SD designation identifies the hub style used on specific Cast Air compressor configurations — not interchangeable with SK-series hubs used on other models\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eOEM Cast Air Replacement:\u003c\/strong\u003e Manufactured to Cast Air specifications — same tolerance fit as the original hub\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003ePrecision Machined Bore:\u003c\/strong\u003e Correct bore tolerance prevents shaft slop and keeps the drive assembly running concentric — a worn or out-of-round hub bore causes vibration and belt alignment problems even with a new belt installed\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eBelt-Drive Application:\u003c\/strong\u003e Designed for belt-driven compressor pump assemblies where the motor drives the pump via sheave and V-belt\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003eTechnical Specifications\u003c\/h3\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003ePart Number:\u003c\/strong\u003e SD138\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eShaft Diameter:\u003c\/strong\u003e 1-3\/8 inch (1.375\")\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eHub Series:\u003c\/strong\u003e SD\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eComponent Type:\u003c\/strong\u003e Replacement motor drive hub\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eApplication:\u003c\/strong\u003e Belt-driven Cast Air compressor pump assemblies\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eManufacturer:\u003c\/strong\u003e Cast Air (Castair)\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003ePrice:\u003c\/strong\u003e $31.57\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003eSD Series Hub Lineup — Choosing the Right Shaft Size\u003c\/h3\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003eSD138\u003c\/strong\u003e — 1-3\/8 inch (1.375\") motor shaft. This product. ($31.57)\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eSD158\u003c\/strong\u003e — 1-5\/8 inch (1.625\") motor shaft — larger motors in 5 HP and above range ($31.57)\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003eFor SK-series hub applications, see SK158 and SK178. SD and SK hubs are different series and are not interchangeable.\u003c\/p\u003e\n\n\u003ch3\u003eWhen Does a Shop Need the SD138\u003c\/h3\u003e\n\u003cp\u003e\u003cstrong\u003eReplace the motor hub when:\u003c\/strong\u003e\u003c\/p\u003e\n\u003cul\u003e\n  \u003cli\u003eThe existing hub shows cracking, bore wear, or visible damage at the keyway or set screw seat\u003c\/li\u003e\n  \u003cli\u003eThe compressor produces unusual vibration, particularly at startup — often a hub that has gone loose on the shaft\u003c\/li\u003e\n  \u003cli\u003eThe belt keeps going out of alignment despite correct tension — a worn hub bore causes pulley runout that no amount of belt tensioning will fix\u003c\/li\u003e\n  \u003cli\u003eYou are installing a replacement motor and the new motor has a 1-3\/8-inch output shaft\u003c\/li\u003e\n  \u003cli\u003ePreventive maintenance stocking — having the correct hub on the shelf means you are not down while waiting for a part when the original fails\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003eWhy Buy From Air Compressor Factory Direct?\u003c\/h3\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003eAuthorized Cast Air dealer since 2016\u003c\/strong\u003e — we stock the complete SD and SK hub range\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eFree shipping\u003c\/strong\u003e on qualifying orders\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eFree technical support\u003c\/strong\u003e at 866-217-0063 — call if you need help confirming whether your compressor uses SD or SK series hubs, or to cross-reference the correct shaft size\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eFull manufacturer warranty\u003c\/strong\u003e on every Cast Air part\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cp\u003e\u003cstrong\u003eCall 866-217-0063 for quick answers and help!\u003c\/strong\u003e\u003c\/p\u003e","brand":"Cast Air","offers":[{"title":"Default Title","offer_id":53342601773269,"sku":"SD138","price":58.22,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0622\/8466\/0949\/files\/CastairReplacementAirCompressorMotorHub_d6f75cda-1061-40aa-bdee-cba087539e8b.png?v=1772652926","url":"https:\/\/aircompressorfactorydirect.com\/products\/castair-replacement-motor-hub-1-3-8-shaft-sd138","provider":"Air Compressor Factory Direct","version":"1.0","type":"link"}