{"product_id":"castair-replacement-motor-pulley-5-8-fixed-bore-shaft-4-od-1b-groove-p1b40-5-8","title":"Castair Replacement Motor Pulley 5\/8\" Fixed Bore Shaft 4\" OD. 1B Groove P1B40-5\/8","description":"\u003ch2\u003eCast Air P1B40-5\/8 — 4\" OD Single-Groove B-Section Motor Pulley, 5\/8\" Fixed Bore\u003c\/h2\u003e\n\n\u003cp\u003eThe Cast Air P1B40-5\/8 is a 4\" outside diameter motor pulley with a single B-section belt groove and a 5\/8\" fixed bore. It mounts directly onto a 5\/8\" motor shaft — no hub required — and drives a B-section V-belt to the compressor pump pulley. This pulley fits the same motor shaft size as the P1A40-5\/8, but uses a B-groove profile rather than an A-groove. The distinction is critical: if your compressor runs a B-belt, you need this pulley. If it runs an A-belt, you need the P1A40-5\/8. Ordering the wrong groove type means the belt will not seat correctly, slippage is immediate, and belt wear is accelerated.\u003c\/p\u003e\n\n\u003cp\u003eThe B-section belt is wider and deeper than an A-section belt — 21\/32\" wide at the top versus 1\/2\" for an A-belt. B-belts handle higher torque loads. Compressors that run on 5\/8\" motor shafts but use B-belts are typically in the higher end of the small-compressor class, where the drive transmits more torque than a single A-belt can reliably carry. If your compressor shipped with a B-belt and you are replacing the motor pulley, this is the correct part.\u003c\/p\u003e\n\n\u003ch3\u003ePulley Specifications\u003c\/h3\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003ePart Number:\u003c\/strong\u003e P1B40-5\/8\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eOutside Diameter:\u003c\/strong\u003e 4\"\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eBore Size:\u003c\/strong\u003e 5\/8\" fixed bore\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eGroove Type:\u003c\/strong\u003e 1B — single groove, B-section belt profile\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eBelt compatibility:\u003c\/strong\u003e B-section V-belt (e.g., B-26, B-29, B-31 — belt length depends on center distance)\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eMounting:\u003c\/strong\u003e Fixed bore — mounts directly on 5\/8\" motor shaft with setscrew and key\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eMaterial:\u003c\/strong\u003e Cast iron\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003eWhy Belt Section Matters\u003c\/h3\u003e\n\u003cp\u003eB-section and A-section belts differ in cross-section dimensions. A B-belt is wider and has a different flank angle than an A-belt. When you put a B-belt in an A-groove, the belt sits too high in the groove and makes minimal contact with the flanks, reducing the friction surface that transmits power. When you put an A-belt in a B-groove, the belt drops too deep and the flanks bottom out. Either way, slippage occurs under load. Use the belt section that matches the original drive specification — and match the pulley groove to that belt section.\u003c\/p\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003eA-section belt + 1A groove:\u003c\/strong\u003e P1A40-5\/8\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eB-section belt + 1B groove (this pulley):\u003c\/strong\u003e P1B40-5\/8\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eB-section belt + 1B groove, 7\/8\" shaft:\u003c\/strong\u003e P1B40-7\/8\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003eFixed Bore vs. Hub Pulleys\u003c\/h3\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003eFixed bore (this pulley):\u003c\/strong\u003e The bore is machined to 5\/8\". Mounts directly on the motor shaft with a key and setscrew. No additional parts needed.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eHub pulleys:\u003c\/strong\u003e The pulley has no machined bore — a separate hub (LX, SD, or SK series) is ordered for the specific shaft size. Useful when the same pulley frame must fit multiple shaft diameters.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eFor 5\/8\" motor shafts:\u003c\/strong\u003e This pulley is the straightforward choice — install directly, no separate hub order required.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003eWhen to Replace the Motor Pulley\u003c\/h3\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003eBelt slipping under load:\u003c\/strong\u003e If the belt slips when the compressor builds pressure despite being correctly tensioned, inspect the groove for wear. A worn groove loses the sharp flank angles that grip the belt.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eVisible groove wear:\u003c\/strong\u003e Look at the groove flanks. If they have worn to a rounded, smooth profile rather than the original angled shape, the pulley needs replacement.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eCracked body:\u003c\/strong\u003e Any crack in the cast iron body is a replacement indicator. A spinning cracked pulley can shed fragments at speed.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eDamaged keyway:\u003c\/strong\u003e If the keyway has rounded corners or the key has been spinning in the slot, the pulley cannot hold its angular position on the shaft reliably.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eWallowed bore:\u003c\/strong\u003e An oversize bore that the setscrew cannot compensate for. This creates runout that accelerates belt wear and increases vibration.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003eSetting Proper Belt Tension\u003c\/h3\u003e\n\u003cp\u003eAfter installing a new pulley and belt, correct tension is critical. A belt that is too loose slips under load and wears rapidly. A belt that is too tight overloads the motor bearings and pump shaft bearings, shortening their service life significantly. The general guideline for V-belt drives on compressors: the belt should deflect approximately 1\/2\" per foot of span under moderate finger pressure (roughly 10 lbs force). Confirm this against the Cast Air service documentation for your specific model.\u003c\/p\u003e\n\n\u003ch3\u003eBelt Guard Compatibility Reference\u003c\/h3\u003e\n\u003cp\u003eCast Air compressor models use specific belt guard sizes. For reference:\u003c\/p\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003e2BG guard (24x16x5):\u003c\/strong\u003e A2, A3, A4, A8 models\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003e3BG guard (32x20x5):\u003c\/strong\u003e C1, D3, G11 models\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003e4BG guard (40x20x5):\u003c\/strong\u003e C2 model\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003e4BG7 guard (40x20x7):\u003c\/strong\u003e C3, G30 models\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003e5BG guard (48x32x7.5):\u003c\/strong\u003e C3U, C4U models\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003eAvailable Motor Pulleys in This Series\u003c\/h3\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003eP1A40-5\/8:\u003c\/strong\u003e 4\" OD, 5\/8\" bore, 1A groove — $30.80\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eP1B40-5\/8 (this pulley):\u003c\/strong\u003e 4\" OD, 5\/8\" bore, 1B groove — $30.80\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eP1B40-7\/8:\u003c\/strong\u003e 4\" OD, 7\/8\" bore, 1B groove\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eP2B series:\u003c\/strong\u003e Dual B-groove pulleys in multiple sizes for larger compressors\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 P1B40-5\/8\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eOutside Diameter:\u003c\/strong\u003e 4.0\"\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eBore:\u003c\/strong\u003e 5\/8\" fixed bore\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eNumber of Grooves:\u003c\/strong\u003e 1\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eGroove Profile:\u003c\/strong\u003e B-section\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eBore Type:\u003c\/strong\u003e Fixed (no hub required)\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eMaterial:\u003c\/strong\u003e Cast iron\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003ePrice:\u003c\/strong\u003e $30.80\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003eWhy Buy From Air Compressor Factory Direct?\u003c\/h3\u003e\n\u003cp\u003eA lot of shops order the wrong pulley because the A\/B groove distinction is easy to miss when you are in a hurry. We can help you confirm the correct groove type for your compressor before you order. Tell us the compressor model number or describe the belt you are running, and we will point you to the right pulley. That is what the tech support line is for.\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 you have the right groove type before ordering\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eFull manufacturer warranty\u003c\/strong\u003e on all Cast Air parts\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eHonest guidance:\u003c\/strong\u003e We stock the full pulley lineup — we will tell you which one is correct, not just sell you whatever is in your cart\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":53342573068501,"sku":"P1B40-5\/8","price":56.8,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0622\/8466\/0949\/files\/MOTOR-PULLEYS-300x248_8f735cb3-8847-40d0-91ee-14fafd39a207.jpg?v=1772652760","url":"https:\/\/aircompressorfactorydirect.com\/products\/castair-replacement-motor-pulley-5-8-fixed-bore-shaft-4-od-1b-groove-p1b40-5-8","provider":"Air Compressor Factory Direct","version":"1.0","type":"link"}