Sprockets
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Frequently asked questions
What information do I need to choose a replacement sprocket?
You need the chain size (for example 40 or 08B), number of strands, number of teeth, hub type, bore diameter and keyway. Counting the teeth on the sprocket is the most reliable method, since the outside diameter may be off due to wear. The sprocket must match the A or B series of the chain in use.
What do sprocket types A, B and C indicate?
Type A is a flat plate without a hub, type B has a hub on one side, and type C has hubs on both sides. Hub type affects the shaft engagement length and the chain line, so changing type can misalign the drive with the opposite sprocket. Measure from the hub face to the tooth centre when replacing.
How do I recognise a worn sprocket?
Worn teeth look hooked, have pointed tips, or show polished wear on one side of the flank. One-sided wear indicates the two sprockets are not aligned. Replace worn sprockets together with new chain so the new chain is not damaged.
What is the minimum number of teeth for a small sprocket?
For normal drives, the driving sprocket should have 17 teeth or more to reduce speed variation and wear. Higher speeds need more teeth, while sprockets under 12 teeth are for low speed only. Hardened teeth help small sprockets resist wear, since each tooth engages more often.
Should sprockets be replaced along with a new chain?
Yes, a new chain on worn sprocket teeth will not seat properly and will elongate much faster. At minimum, replace the small sprocket, since it engages more often and wears quicker. Conversely, fitting a stretched old chain on new sprockets also wears them quickly.
How do I check sprocket alignment?
Lay a straight edge or taut string across the faces of both sprockets to confirm they are in the same plane. Also check that the two shafts are parallel both horizontally and vertically. Wear on one side of the teeth and on the link plates is a clear sign of misalignment.
Are hardened teeth necessary on a sprocket?
Induction hardened teeth resist wear far better than plain steel teeth, so they suit high speed, heavy load or abrasive dust. Small sprockets with few teeth are the first candidates for hardening because each tooth engages more often. For light loads at low speed, unhardened sprockets are usually adequate.
What needs specifying when a sprocket is rebored and keyed?
Please give the bore diameter and tolerance, the keyway size to its standard (DIN 6885 or ANSI), and the number and position of set screws. Also check that the hub wall remains thick enough after a large rebore so it does not crack when the screws are tightened. If the bore is too large for the hub, a taper bush sprocket is the better choice.
