Quick answer: sometimes you can keep the old sprockets, but the bar is high. The new belt has to engage the existing tooth form exactly, and matching pitch does not guarantee that, because two belts at the same pitch can have different drive bar shapes and pocket depths. A matched belt and sprocket set has an easier job: it only has to fit the conveyor frame and the drive shaft. That is what we recommend, and the three numbers at the end of this article are what let us quote it.
What the sprocket is actually engaging
A modular belt is a positive drive product. The sprocket teeth sit in pockets moulded into the underside of the belt and push it along. Nothing relies on friction, which is why these belts run wet, cold and slack.
That makes the tooth and the pocket a mating pair with real tolerances. Pitch sets where the pockets are along the belt. It says nothing about how deep they are, how the drive face is angled, or how wide the tooth can be before it fouls the module. Two 25.4 mm belts from different moulds can both look correct on paper, and one of them will ride up the teeth under load.
So the honest answer has two halves. Same series as before, sprockets in good condition, yes. A different series at the same pitch, and we cannot promise engagement without seeing the sprocket, and neither can anyone else.
The two paths, side by side
| Keep the existing sprockets | Buy belt and sprockets as a set | |
|---|---|---|
| What has to match | Tooth form, pocket depth, tooth width, pitch, plus the column opposite | Shaft size and bore type, hub width, frame clearance |
| How it is verified | Photographs of the teeth, or in a hard case a sample sprocket | Three numbers off the shaft and the frame |
| Risk carried by | You, on the new belt | Shared, and much smaller |
| Cost position | Saves the sprocket line on the order | A small fraction of a belt order priced by area |
| Sensible when | Same series, sprockets recently changed, teeth clean | Series is changing, or the sprockets are original to the machine |
Our position is plain. If the sprockets went on with the machine and the belt has run three or four years, change them with the belt. A worn sprocket is the most reliable way we know to ruin a new belt, and the saving is small against a belt priced by area.
How to inspect a sprocket before you decide
Stop the line, get a torch, and turn the drive shaft by hand through a full revolution while you watch. Five things tell you almost everything.
| What you see | What it means | Verdict |
|---|---|---|
| Teeth hooked, with the drive face worn back so the tooth curves like a shark fin | The tooth has lost its flank. It no longer pushes the pocket squarely, it wedges into it. | Replace. This shape will chew a new belt fast. |
| Pockets between teeth visibly widened, tooth roots thinned | Years of grit acting as a lapping compound. Engagement is now loose in both directions. | Replace. |
| Sprocket wobbles side to side as the shaft turns | The bore has opened up, or axial location has gone. The belt gets a sideways push once per revolution. | Replace the sprocket and check the shaft and the locating bushings. |
| One sprocket on the shaft clearly more worn than its neighbours | Load is not shared. Usually a spacing or alignment fault. | Replace the set and fix the alignment, or it repeats. |
| Teeth full and square, edges crisp, no rocking | The sprockets have life in them. | Keeping them is reasonable if the series is unchanged. |
Two practical notes. Compare a drive sprocket with an idler or a return wheel on the same machine, because the idler sees far less load and shows what an unworn profile looks like on your own equipment. And photograph the teeth in profile, from the side. A front view hides exactly the wear you are looking for.
Why a worn sprocket destroys a new belt
A hooked tooth does not push the pocket, it climbs it. The belt lifts slightly off the sprocket at each engagement, drops back, and the shock lands on the hinge rods and the module drive bars. On a new belt the pockets are still tight, so the mismatch is at its worst on day one rather than settling in.
The failures that follow are the ones people describe as sudden. Modules cracking at the drive bar. A belt jumping a tooth under load and then running out of square. Hinge rods migrating sideways. All of these read as belt defects, and the tracking, wear and slip symptoms they produce all trace back to wear on the drive.
A quieter version exists too. A slightly worn sprocket breaks nothing; it just shortens belt life by a large fraction, and nobody measures that, because the comparison is against a belt that was never fitted.
The three numbers to report
Whether you keep the sprockets or replace them, these three settle the quotation.
1. Series. The sprocket family follows the belt series, so this is the same number that identifies the belt. If you do not have it, measure the belt pitch and count the sprocket teeth and we can work back.
2. Tooth count. Count teeth on one sprocket. It sets the pitch diameter, so it decides where the belt surface sits relative to the frame, and it cannot change without moving the whole drive. These are the counts we hold.
| Series | Tooth counts |
|---|---|
| 300 | 12 |
| 400 | 10 / 12 / 16 |
| 900 | 9 / 12 / 18 / 20 |
| 956 | 8 / 10 / 12 |
| 976 and 986 | 12 / 16 / 20 |
| 1000 | 16 / 18 / 22 |
| 1100 | 16 / 24 / 32 |
| 2400 | 16 |
| 4809 | 9 / 14 |
| 5935 | 9 / 13 / 17 / 24 |
| 7705 | 10 |
| OPB | 8 / 10 / 12 |
3. Bore type and size. Look at the shaft, not at the old sprocket hub. Square shafts and round shafts both appear on the same kinds of line, and the sprocket has to suit what you have.
| Bore | Sizes we hold | Note |
|---|---|---|
| Round | 25 / 30 / 40 mm | Needs a key or a clamping arrangement to transmit torque |
| Square | 40 / 50 / 60 mm | The common choice on modular belt drives, no key required |
| Bushing insert | 30 / 40 / 50 / 60 mm | Adapts a larger sprocket bore down to a smaller shaft |
Measure the shaft across the flats if it is square, across the diameter if it is round, and take the reading somewhere clean, away from where the sprockets have sat for years.
Flat top chain is a different question
If your line runs flat top chain rather than modular belt, the drive parts are drive and idler wheels, which sit in the parts list for a chain conveyor rebuild alongside the wear strips and pins, and the same inspection applies with one addition: check the wheel for a worn groove where the chain plate has been tracking. A grooved wheel holds the new chain off its correct running line.
This is the replacement decision, not the selection decision
Everything above assumes an existing conveyor with an existing drive. Choosing sprockets for a new line is a different exercise: how many to fit per metre of belt width, which one is fixed and which float on the shaft, how tooth count interacts with line speed, all of it covered in our note on sprocket tooth count, bore and shaft layout. If that is your situation, start from the sprocket and drive wheel range and tell us the belt width and duty.
What to send with the enquiry
- Series, tooth count, bore type and bore size, the three numbers above
- One photo of the teeth in profile, from the side
- How many sprockets are on the drive shaft, and the shaft length between bearings
- Belt width and metres required, so we can check sprocket spacing against the belt
- Whether the belt series is staying the same or changing
If you are not sure of the series, the method for getting there from the belt itself is in our guide on measuring a modular belt for replacement, and the entry point for an unknown belt is identifying a belt from a photo or a part number.
Send the three numbers and a profile photo of the teeth through WhatsApp or the contact form. If the sprockets are sound we will say so and quote the belt alone.
