A customer asks for a chain. The sprockets look serviceable. You sell a chain, and they are back in two months. This is not bad luck - it is mechanically inevitable, and it is worth being able to explain at the counter.
How the wear couples. A drive chain does not stretch in the metallurgical sense. Its pins and bushes wear, and the effective pitch grows. The sprocket teeth wear to match that grown pitch, developing a hooked profile. Put a new chain with correct pitch onto a sprocket cut to a longer one and the load lands on one or two teeth instead of being shared across eight or ten. Contact pressure goes up several-fold, and the new chain wears at a rate the customer will notice within weeks.
The reverse is equally true. New sprockets with a worn chain get their teeth hooked almost immediately. Either half-measure destroys the new component.
How to check wear properly. For the chain: pull a link away from the rear sprocket at the three-o-clock position. If you can lift it far enough to expose more than about half a tooth, the chain is finished. Better, measure a 20-link span against the specification. For sprockets: look at the tooth profile from the side. New teeth are symmetrical; worn teeth lean, with a concave leading face and a hooked tip. Any hooking means replacement.
Specify the kit correctly. A kit is chain, front sprocket and rear sprocket. You need chain pitch and link count, front and rear tooth counts, and whether the chain is a standard or O-ring type. Changing tooth counts changes final drive: fewer rear teeth gives higher top speed and weaker acceleration; more rear teeth reverses that. Do not change the ratio without telling the customer.
Fitting notes that decide the life of the kit. Set slack to specification with the rider weight considered, not with the bike on the stand only. Check wheel alignment on both adjuster marks - a misaligned wheel wears one side of every tooth. Fit the master link clip with the closed end facing the direction of travel. Lubricate on assembly and keep it lubricated; a dry chain in Mumbai monsoon grit is a consumable measured in weeks.
What we stock. Rockman drive chain kits and cam chain kits, and D.I.D chains. We price and supply them as kits because that is how they should be fitted, and because a kit is cheaper than a chain plus two sprockets bought separately three months apart.
Cam chains follow the same logic, incidentally - replace the tensioner and guides with the chain, or the new chain will be slapping again inside a year.
You can, but a new chain on worn sprockets typically wears out several times faster because load concentrates on a few teeth. Replacing as a kit is cheaper over the life of the parts.
Pull a link away from the rear sprocket at the three-o-clock position. If it lifts far enough to expose more than about half a tooth, replace the kit. Hooked or leaning sprocket teeth confirm it.
We stock it. Send the part code for same-working-day confirmation.
