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J Section Pulleys

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J Section Pulleys

J section pulleys are sheaves with a grooved wheel that accommodates a J-section V-belt in belt-driven machinery. They are used for power transmission in a multitude of electrical, petrol, diesel or even mechanical machinery, including lawnmowers, power tools, farm equipment, industrial conveyors, wood lathes, vehicles, and exercise equipment. The trapezoidal cross-sections of their V-belts make them suitable for high speed, high ratio, high torque and high tension applications, and they provide smooth running and low noise operation.

Belts with multiple longitudinal ribs are called poly-V-belts and these transmit more power from a smaller diameter pulley. Sheaves machined for as many as 20 ribs exist, although 4-8 ribs are much more common. On J-section sheaves and belts, the pitch of grooves and ribs is 2.34mm or 0.092". Other sections you may encounter are K, L and M, with pitches of up to 9.4mm. We are happy to source for you any type or size of pulley or belt you require, and we have a comprehensive range of matching v-belts available in various sections, lengths and materials.

Poly-V drive systems are low maintenance and able to transmit 600kW of power using a single belt, with up to 98% efficiency. Up to 20:1 speed ratios are easily attainable and as much as 60:1 with some specially designed pulleys. Switching to smaller diameter poly-V drives is also advantageous for noise reduction.

J section pulleys are usually made from surface-treated cast iron, but they are also available in stainless steel and aluminium.


J section pulleys have either a tapered bore or pilot bore. Tapered bore pulleys are not intended for tapered shafts, rather it denotes that they are fitted using tapered locking bushes onto conventional parallel shafts. Pilot bore pulleys are so called because they come with a basic pilot hole to assist machining to your exact shaft requirements, and this is the kind more often used for tapered shafts or other unusual shafts with small or non-standard diameters or keyways.

Tapered bore pulleys are easily fitted, without additional machining, onto a range of shaft diameters with standard keyways, whether imperial or metric. Split tapered locking bushes adapt their bore down to the shaft. The bush is usually mounted into the pulley with two grub screws (or sometimes an allen key), which compress the bush into the pulley and clamp it to the shaft as they're tightened.

Typically, the bush has two plain opposing holes, and often a third tapped hole in line with the split. The holes align with those in the pulley and the bush slips easily in when correctly orientated. Don't fully tighten the grub screws until the assembly is located on the shaft. If present, the unoccupied tapped hole is there to aid removal. Extract the two grub screws but re-insert one into this hole in line with the split. As it's tightened, the bush rises from the pulley.

Purchase online from Simply Bearings for best advice, immediate dispatch, and impeccable customer service.


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