Cast Air P2B335-7/8 — 3.35" OD Dual-Groove B-Section Motor Pulley, 7/8" Fixed Bore
The Cast Air P2B335-7/8 is a 3.35" outside diameter motor pulley with two B-section belt grooves and a 7/8" fixed bore. It mounts directly onto a 7/8" motor shaft and drives a dual B-belt setup to the compressor pump. Dual-groove pulleys are used on compressors where a single belt cannot transmit the required torque reliably — the two belts share the load, which reduces slippage under peak demand and extends belt service life. This is the smallest OD in the Cast Air dual-B-groove motor pulley lineup, which makes it appropriate for applications where you need to run the pump at a lower speed relative to motor RPM.
Pulley diameter controls pump RPM. A smaller motor pulley produces a lower pump speed for a given motor speed. If your compressor is correctly specified with a 3.35" motor pulley and you are replacing a worn or damaged unit, match the 3.35" OD exactly. Do not substitute a larger diameter unless you are intentionally increasing pump speed — and if you are doing that, you need to verify that the pump and motor can handle the increased load and speed.
Pulley Specifications
- Part Number: P2B335-7/8
- Outside Diameter: 3.35"
- Bore Size: 7/8" fixed bore
- Number of Grooves: 2
- Groove Profile: B-section
- Belt compatibility: Two B-section V-belts (matched pair recommended)
- Mounting: Fixed bore — mounts directly on 7/8" motor shaft with key and setscrew
- Material: Cast iron
- Price: $38.50
Why Two Belt Grooves?
Single-belt drives work fine for low-to-moderate torque applications. When the compressor gets larger — higher displacement, higher pressure, larger motor — the torque demand on the belt drive exceeds what a single B-belt can reliably transmit. Dual-belt drives solve this by splitting the load between two belts:
- Higher torque capacity: Two B-belts can transmit roughly twice the torque of a single B-belt at the same pulley diameter
- Reduced slippage: Less chance of belt slip under startup load spikes, which is when most belt damage occurs
- Longer belt life: Each belt runs cooler and with lower unit stress than a single belt doing all the work
- Use matched belt pairs: When replacing belts on a dual-groove drive, replace both belts at the same time with a matched pair. Mismatched belts (different brands, different ages) will have slightly different lengths and one belt will carry more load than the other, causing uneven wear and premature failure.
Pulley Diameter and Pump Speed
The 3.35" OD is the smallest motor pulley in the Cast Air 2B lineup. Here is how it compares to others in the series, and what that means for pump RPM:
- Smaller motor pulley = slower pump: A 3.35" motor pulley driving a 10" pump pulley on a 1750 RPM motor results in a pump speed of approximately 586 RPM
- Larger motor pulleys produce higher pump speed: A 4.95" motor pulley in the same configuration would produce 866 RPM at the pump
- Replace with the same OD: If you are replacing a worn pulley, the 3.35" OD is the specification that the compressor was designed around. Match it exactly.
- If you are tuning the drive ratio: Any change in pulley diameter changes pump speed, output CFM, and motor load. Calculate the new pump RPM and verify it is within the pump manufacturer's specified operating range before making the change.
Fixed Bore vs. Hub Pulleys
- Fixed bore (this pulley): Machined to 7/8". Mounts directly on the motor shaft. No additional parts required beyond a matching key.
- Hub pulleys: Require a separate hub ordered for the specific shaft size. See the P2B355H, P2B395H, P2B445H, and P2B495H for hub-style pulleys in the dual B-groove lineup.
- For 7/8" shafts: The P2B335-7/8 is the direct, no-hub option at 3.35" OD. If you need a different OD with a 7/8" shaft, a hub-style pulley with an LX78 hub is the path to other diameters.
Belt Guard Compatibility
Dual-groove pulleys in the Cast Air lineup are used with specific belt guards. For reference:
- 2BG guard (24x16x5): A2, A3, A4, A8 models
- 3BG guard (32x20x5): C1, D3, G11 models
- 4BG guard (40x20x5): C2 model
- 4BG7 guard (40x20x7): C3, G30 models
- 5BG guard (48x32x7.5): C3U, C4U models
2B-Groove Motor Pulley Lineup Comparison
- P2B335-7/8 (this pulley): 3.35" OD, 7/8" fixed bore — $38.50
- P2B355H: 3.55" OD, hub shaft — $38.50
- P2B395H: 3.95" OD, hub shaft — $38.50
- P2B445H / P2B455H: 4.45"-4.55" OD, hub shaft
- P2B495H: 4.95" OD, hub shaft — $66.41
- P2B625-13/8: 6.25" OD, 1-3/8" fixed bore
- P2B675-13/8: 6.75" OD, 1-3/8" fixed bore
- P2B725-11/8: 7.25" OD, 1-1/8" fixed bore
- P2B80-13/8: 8.0" OD, 1-3/8" fixed bore
- P2B875-13/8: 8.75" OD, 1-3/8" fixed bore
Technical Specifications
- Part Number: P2B335-7/8
- Outside Diameter: 3.35"
- Bore: 7/8" fixed bore
- Number of Grooves: 2
- Groove Profile: B-section
- Bore Type: Fixed (no hub required)
- Material: Cast iron
- Price: $38.50
Why Buy From Air Compressor Factory Direct?
Dual-groove pulleys are not a part you want to get wrong — if the OD is off, your pump speed changes; if the bore is wrong, the pulley does not go on the shaft. We stock the full Cast Air motor pulley lineup. Call us with your compressor model number and we will confirm the correct pulley before you order.
- Free shipping on qualifying orders
- Free tech support: Call 866-217-0063 — we will confirm the OD and bore against your compressor model
- Full manufacturer warranty on all Cast Air parts
- Honest guidance: We will tell you if there is a better match for your specific application
Call 866-217-0063 for quick answers and help!
