{"product_id":"castair-adjustable-belt-tensioner-base-for-20hp-motors","title":"Castair, Adjustable Belt Tensioner Base for 20HP Motors","description":"\u003ch2\u003eCastair Adjustable Belt Tensioner Base — 256D, 20 HP Motors\u003c\/h2\u003e\n\u003cp\u003eThe Castair 256D is the adjustable belt tensioner base for Castair belt-drive air compressors using 20 HP motors. This is the base component — the slide plate and adjustment bracket — not a complete tensioner assembly. If your tensioner mechanism is functioning but the base is bent, cracked, or stripped, the 256D gets your compressor back to proper belt tension without replacing the full assembly.\u003c\/p\u003e\n\u003cp\u003eAt $186.34, the 256D is one of the more cost-effective major component replacements for a 20 HP compressor. A 20 HP belt-drive unit moves substantial power through the drive belt — proper tensioner base function is not optional. A failed base that cannot hold the motor in position leads to belt slip under load, heat generation, and accelerated wear across the entire drive system.\u003c\/p\u003e\n\u003ch3\u003ePart Details\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003ePart Number:\u003c\/strong\u003e 256D\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eType:\u003c\/strong\u003e Adjustable belt tensioner base (slide\/bracket — no tensioner mechanism included)\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eCompatible Motor Size:\u003c\/strong\u003e 20 HP\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 $186.34\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch3\u003eTensioner Base Function on a 20 HP Compressor\u003c\/h3\u003e\n\u003cp\u003eOn a 20 HP belt-drive compressor, the motor mounts on a sliding base that moves along adjustment slots to change the motor-to-pump sheave center distance. Moving the motor away from the pump increases belt tension. Once set correctly, the motor is bolted in position on the base. As the belt stretches with use, the base allows readjustment to compensate for belt elongation.\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eSliding adjustment:\u003c\/strong\u003e Motor position changes along the base to set and maintain belt tension\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eLock-down mechanism:\u003c\/strong\u003e Bolts secure the motor at the correct tension position under the torque loads of a 20 HP drive\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eStructural requirement:\u003c\/strong\u003e The base must handle the reaction forces from belt tension — a 20 HP drive puts substantial radial load on the motor mount\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch3\u003eHow the 256D Fits in the Castair Tensioner Family\u003c\/h3\u003e\n\u003cp\u003eCastair uses different tensioner base part numbers matched to motor HP and frame size. The 256D is the 20 HP base. For comparison:\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003e215D ($138.91):\u003c\/strong\u003e Tensioner base for 7.5-10 HP, 215 frame motors\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e254D ($186.34):\u003c\/strong\u003e Tensioner base for 15 HP, 254 frame motors\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e256D ($186.34, this part):\u003c\/strong\u003e Tensioner base for 20 HP motors\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e284D ($203.28):\u003c\/strong\u003e Tensioner base for 25-30 HP, 284 frame motors\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003eConfirm your motor HP before ordering — the different bases are not interchangeable between HP classes.\u003c\/p\u003e\n\u003ch3\u003eWhen Does a Shop Need This Part?\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eBent or cracked base plate:\u003c\/strong\u003e Physical damage to the base prevents smooth motor adjustment and belt tension maintenance\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eStripped adjustment slots or lock-down hardware:\u003c\/strong\u003e If the motor cannot be secured at the correct tension position, the base needs replacement\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eTensioner mechanism is intact, base is failed:\u003c\/strong\u003e When you can confirm the mechanism works, the 256D base-only saves over a full assembly purchase\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eCompressor build or rebuild:\u003c\/strong\u003e Sourcing the correct OEM base for your motor HP ensures proper alignment from first startup\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch3\u003eTechnical Specifications\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003ePart Number:\u003c\/strong\u003e 256D\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eManufacturer:\u003c\/strong\u003e Cast Air (Castair)\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eMotor HP:\u003c\/strong\u003e 20 HP\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eType:\u003c\/strong\u003e Adjustable tensioner base only\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eList Price:\u003c\/strong\u003e $186.34\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003e\u003cem\u003eNote: Manufacturer product page data was not available at time of writing. Specifications are derived from the product name and part number. Contact us to confirm fit for your specific Castair compressor model before ordering.\u003c\/em\u003e\u003c\/p\u003e\n\u003ch3\u003eWhy Buy From Air Compressor Factory Direct?\u003c\/h3\u003e\n\u003cp\u003eWe have specialized in air compressor parts and equipment since 2016. Castair belt tensioner bases are part of our regular inventory across the HP range. Call us with your compressor model number to confirm the 256D is the correct base for your 20 HP application, or whether a related part applies.\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eFree shipping\u003c\/strong\u003e on qualifying orders\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eFree tech support:\u003c\/strong\u003e Call 866-217-0063 to confirm the right part for your compressor\u003c\/li\u003e\n\u003cli\u003e\u003cstrong\u003eFull manufacturer warranty\u003c\/strong\u003e\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eHonest guidance:\u003c\/strong\u003e We stock the full range of Castair tensioner bases and will point you to the correct one\u003c\/li\u003e\n\u003c\/ul\u003e\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":53342503960789,"sku":"256D","price":343.64,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0622\/8466\/0949\/files\/Screenshot_27_43c779c9-bcfa-4cc3-8159-7d8e675271d6.png?v=1772652477","url":"https:\/\/aircompressorfactorydirect.com\/products\/castair-adjustable-belt-tensioner-base-for-20hp-motors","provider":"Air Compressor Factory Direct","version":"1.0","type":"link"}