{"product_id":"castair-p1b40-7-8","title":"Castair P1B40-7\/8","description":"\u003ch2\u003eCast Air P1B40-7\/8 — 4\" OD Single-Groove B-Section Motor Pulley, 7\/8\" Fixed Bore\u003c\/h2\u003e\n\n\u003cp\u003eThe Cast Air P1B40-7\/8 is a 4\" outside diameter motor pulley with a single B-section belt groove and a 7\/8\" fixed bore. This is the same 4\" diameter and B-section groove profile as the P1B40-5\/8, but machined to fit a 7\/8\" motor shaft instead of a 5\/8\" shaft. If you are replacing the motor pulley on a compressor with a 7\/8\" motor output shaft that runs a single B-belt, this is the correct part. The bore is fixed — no separate hub is needed — and the pulley mounts directly onto the shaft with a key and setscrew.\u003c\/p\u003e\n\n\u003cp\u003eThe 7\/8\" bore is a common motor shaft size in the 1 HP to 3 HP range on single-phase motors, and in some fractional-horsepower three-phase motors. If your compressor has a larger frame motor — one step up from the 5\/8\" shaft motors that drive the smallest compressors — there is a good chance your motor shaft is 7\/8\". Measure the shaft before ordering. The difference between 5\/8\" (0.625\") and 7\/8\" (0.875\") is significant — a 5\/8\" bore pulley will not go onto a 7\/8\" shaft, and a 7\/8\" bore pulley on a 5\/8\" shaft creates dangerous runout.\u003c\/p\u003e\n\n\u003ch3\u003ePulley Specifications\u003c\/h3\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003ePart Number:\u003c\/strong\u003e P1B40-7\/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 7\/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 (B-26, B-29, B-31, etc. — belt length determined by center distance)\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eMounting:\u003c\/strong\u003e Fixed bore — mounts directly on 7\/8\" motor shaft with key and setscrew\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eMaterial:\u003c\/strong\u003e Cast iron\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003eIdentifying Your Motor Shaft Size\u003c\/h3\u003e\n\u003cp\u003eBefore ordering, confirm your motor shaft diameter. Do not guess — an incorrectly bored pulley creates runout and vibration that damages bearings and shortens compressor life.\u003c\/p\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003eMeasure with calipers:\u003c\/strong\u003e Remove the existing pulley and measure the shaft diameter directly. A 7\/8\" shaft will measure 0.875\".\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eCheck the motor nameplate:\u003c\/strong\u003e Motor shaft size is sometimes listed on the nameplate or in the motor datasheet. Look for the frame designation — a 56 frame motor typically has a 5\/8\" shaft, while a 143T or 145T frame motor has a 7\/8\" shaft.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eCheck the original pulley:\u003c\/strong\u003e The bore size is sometimes stamped or cast into the pulley body, or it may be in the Cast Air parts list for your compressor model.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eCall us:\u003c\/strong\u003e Give us the compressor model number and we will tell you the correct bore size.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003eHow Motor Pulley Diameter Affects Pump RPM\u003c\/h3\u003e\n\u003cp\u003eThe motor pulley is the primary variable you use to set pump speed. The formula is straightforward:\u003c\/p\u003e\n\u003cul\u003e\n  \u003cli\u003e\u003cstrong\u003ePump RPM = (Motor RPM × Motor Pulley OD) ÷ Pump Pulley OD\u003c\/strong\u003e\u003c\/li\u003e\n  \u003cli\u003eWith a 4\" motor pulley and a 10\" pump pulley on a 1750 RPM motor: pump runs at 700 RPM\u003c\/li\u003e\n  \u003cli\u003eChanging the motor pulley from 4\" to 4.5\" increases pump RPM by 12.5% — which increases output CFM but also increases motor load\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eDo not change pulley diameter without verifying the motor can handle the additional load.\u003c\/strong\u003e Overspeeding the pump overloads the motor and can cause overheating, tripped breakers, or motor failure.\u003c\/li\u003e\n  \u003cli\u003eThis pulley is a replacement part — match the original 4\" OD unless you are intentionally re-engineering the drive ratio with engineering support\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003eB-Section Belt — What That Means\u003c\/h3\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003eB-section belt:\u003c\/strong\u003e 21\/32\" wide at the top, 13\/32\" deep, standard V-belt cross section used on medium-duty drives\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eA-section belt:\u003c\/strong\u003e 1\/2\" wide at the top, used on lighter-duty single-belt drives — NOT compatible with this pulley's B-groove\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eCross-section match is required:\u003c\/strong\u003e The belt must match the groove. B-belt in a B-groove only.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eIf your compressor runs an A-belt:\u003c\/strong\u003e You need the P1A40-5\/8 (for 5\/8\" shafts) — there is no 1A groove pulley with 7\/8\" bore in the Cast Air lineup at 4\" OD; contact us to discuss options\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 slips under load despite correct tension:\u003c\/strong\u003e Groove wear prevents the belt flanks from making adequate contact with the pulley flanks\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eVisible groove wear:\u003c\/strong\u003e Smooth, rounded groove flanks instead of sharp angled surfaces indicate the pulley needs replacement\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eCracked body:\u003c\/strong\u003e Cast iron is brittle. Any visible crack means immediate replacement.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eDamaged keyway:\u003c\/strong\u003e A wallowed or rounded keyway allows the pulley to shift angularly on the shaft, causing shock loads and premature belt and bearing failure\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eExcessive vibration:\u003c\/strong\u003e A pulley that is out of round (from impact or manufacturing defects) creates cyclical vibration that shortens bearing life\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003eComparing the 4\" Fixed-Bore Motor Pulleys\u003c\/h3\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003eP1A40-5\/8:\u003c\/strong\u003e 4\" OD, 5\/8\" bore, A-groove — for 5\/8\" shafts with A-belts\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eP1B40-5\/8:\u003c\/strong\u003e 4\" OD, 5\/8\" bore, B-groove — for 5\/8\" shafts with B-belts\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eP1B40-7\/8 (this pulley):\u003c\/strong\u003e 4\" OD, 7\/8\" bore, B-groove — for 7\/8\" shafts with B-belts\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 P1B40-7\/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 7\/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\u003c\/ul\u003e\n\n\u003ch3\u003eWhy Buy From Air Compressor Factory Direct?\u003c\/h3\u003e\n\u003cp\u003eOrdering the wrong bore size is one of the most common pulley mistakes. We see it regularly — shops order the 5\/8\" bore version when their motor has a 7\/8\" shaft. We would rather you call us first, confirm the shaft size, and order the correct pulley. We stock the full Cast Air motor pulley lineup and can have the right part to you quickly.\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 — we will help you confirm the correct bore and groove before you order\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 If the P1B40-7\/8 is not the right part for your compressor, we will tell you what is\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":53342573232341,"sku":"P1B40-7\/8","price":0.0,"currency_code":"USD","in_stock":true}],"url":"https:\/\/aircompressorfactorydirect.com\/products\/castair-p1b40-7-8","provider":"Air Compressor Factory Direct","version":"1.0","type":"link"}