S2M / S3M / S5M / S1.5M Timing Pulley (all types)

S-series pulleys · 4 models · Bore 4–8mm · 3 types · 13 options in stock

S-series timing pulleys — S1.5M, S3M and S5M. The parameters are listed in order of importance: the one at the top decides the most, and no amount of care further down makes up for getting it wrong.

This page lists 13 options: Model S1.5M / S2M / S3M / S5M, Bore 4–8mm (4 options), Type BF type / Idler gear with teeth / K type, Tooth count 15–60 (7 options), Belt width 10 / 15 / Not specified. From ¥3.9.

The parts of this item

Figure 1 — A pulley needs four numbers: teeth, pitch (type), belt width, bore — all four must match the belt

What each parameter decides

Every parameter below shows the real range available on this page, and what goes wrong if you pick it wrong. Work through them in this order and you will not go far wrong.

How to choose, step by step

1. Tooth form first — Timing pulleys are classed by tooth form (2GT, HTD 3M, HTD 5M...). Gears are classed by module (M1, M1.5, M2...). These are two different systems.
2. Tooth count — Tooth count sets the ratio and the pitch diameter.
3. Bore — 4–8mm (4 options) or 4–8mm (4 options). It has to fit your shaft, and a bore 0.1 mm oversize will not clamp.
4. How it is fixed — Set screw, clamp or keyway.

How the options on this page are distributed

Figure 2 — how the 13 options on this page are spread across each parameter: the bars on the left show how many options sit in each band, the panel on the right shows the real range of every parameter and how many steps it has.

Variant quick reference

Reading the part numbers

You can order by part number or by selecting the parameters. The part number is fastest, but it does not always encode every parameter — the selector on this page is the authority.

7 common mistakes

1. A pulley is not a gear. One drives a belt, the other meshes with another gear. The tooth forms are not related.
2. Gears need the same module to mesh. Different module means different tooth spacing and they will not run together at all.
3. Pitch diameter is not outside diameter. Centre distance is calculated from pitch diameter — use the OD and the gears bind.
4. Set screws mark the shaft. On a precision shaft use a clamp type or mill a flat.
5. Check the face width. A belt wider than the pulley walks off the flange.
6. Measure before you order. Take the old part off and measure it, or send us a photo with the caliper reading — that beats guessing from a model number every time.
7. Everything here is in millimetres. Where a size is imperial, convert it: 1" = 25.4 mm, 1/4" = 6.35 mm, 3/32" = 2.38 mm.

When to replace it

You do not replace this until it fails — but "still looks usable" and "still reliable" are two different things. Any one of these and it is time:

• Tooth flanks worn into a step, or pitting.
• Flanks polished bright and the backlash clearly increased, with noise.
• Bore worn oversize and the set screw no longer grips.

Fitting and use

Check before assembly

• Wipe every mating surface with a lint-free cloth. No chips, no burrs, no old grease. One chip is enough to make a bearing noisy.
• Measure the fits — shaft, bore, centre height — against nominal. More than 0.02 mm out and you should check whether you have the right part.
• Check the orientation: the side with the shoulder, step or oil hole has to face the right way. Fitted backwards, it is usually scrap on removal.

Assembly

• Press if you can; do not hammer. If you must tap, use a brass or nylon drift and put the force on the ring that is being fitted, never through the raceway.
• For an interference fit, heat to 80–100 °C first (oil bath or hot plate — never an open flame on a bearing). Hot fitting is easier and safer than cold pressing.
• Tighten fasteners in a diagonal pattern in 2–3 stages. Taking one down fully first distorts the housing and cocks the shaft.

Running in

• Turn it by hand first. It should be smooth, with no tight spot and no axial play. If there is a tight spot, loosen and reseat — do not run it in.
• Run it slowly and unloaded for 10–20 minutes, then feel the temperature. A clear rise means too much preload or poor alignment.
• Re-torque the fasteners after running in, then apply load.

Three things not to do

• Do not hammer. It brinells the raceway, you cannot see it, and it whines forever afterwards.
• Do not mix brands or precision classes in a matched pair. The load shares unevenly and the poorer one always fails first.
• Do not skip lubrication on parts that need it. A few hundred hours dry and it seizes.

Matching parts

• Belt of the same tooth form
• Motor and shaft

Lead time, custom work and shipping

• Stock sizes: dispatched in 1–2 working days, subject to stock
• Custom: non-standard sizes, materials and treatments are possible — send quantity and drawing
• Shipping: from Shenzhen; domestic courier by default, DHL or dedicated line for export
• Volume: quantity pricing available, contact us for a quote

If you cannot find the size you need, or you are not sure which one fits, send us the problem you are solving — what machine it goes on, the dimensions of the part you have, what it has to achieve — and we will match it.