How to change worn sprockets

Keep your wheels turning sweetly with a new set of cogs

1 Check for wear

Most bikes transfer power from the engine to the rear wheel via two sprockets and a chain. All three of these components have a service life that varies based upon the type of bike, style of riding and most crucially the correct amount of maintenance they have received. Signs of a worn sprocket include hooked or broken sprocket teeth and excessive transmission noise.

2 Count your teeth

When ordering new sprockets, it is essential to get the one with the correct number of teeth to maintain your final drive ratio (it is possible to use larger or smaller sprockets for more top speed or acceleration). Deviating from the standard spec can change the bike’s acceleration performance, cause a drop in fuel efficiency and cause speedo inaccuracies.

3 Make your mark

The front sprocket cover needs to be removed. On this Yamaha Fazer 600 it also requires the gear lever to be removed from the spline. Mark the spline with a marker pen prior to removal so that you know which way it needs to go when re-installed. With the gear lever off, undo the bolts that fasten the front sprocket cover and remove the cover completely.

4 Tap off the tab

With clear access to the front sprocket have a look to see if there is a locking tab washer behind the nut that retains the front sprocket. If there is one, like here on our Yamaha Fazer 600, it needs to have the tab tapped back so that the nut can be removed. You can do this by using a straight-edged tool or screwdriver.

5 Crack the nut

With the tab washer removed, find a socket that fits the retaining nut. Use at least a half-inch drive, ideally a single hexagon type, fitted to a long-handled breaker bar. Owing to the high torque it will take a fair amount of leverage to undo it, so ask someone to steady the bike.

6 Out with the old…

Wind out the chain adjusters then remove the front sprocket and install the new one. Put the tab washer on and make sure it’s lined up on the spline. Refit the retaining nut with the recessed side facing the sprocket. Tighten the nut to the correct torque and bend the tab over one side of the nut.

7 Renew the rear

Now turn your attention to the rear. With the bike on a paddock stand, remove the back wheel and lay it flat on the floor. Undo the nuts that retain the rear sprocket, making sure to keep them safe for installation later. Just as you did with the front sprocket, make sure the new rear sprocket is the correct type and size.

8 Criss-cross nuts

Now place the new sprocket on the hub and tighten up the nuts by hand. If there are no locking tabs, all the sprocket nuts should be of the self-locking type. Tighten them up in a criss-cross sequence of diagonal pairs first, then use a torque wrench to torque them up to the value listed in your bike’s workshop manual.

9 Tension the chain

Reinstall the rear wheel then tension the chain as per your workshop manual. Use the tension mark increments to help get the adjustment equal on both sides. When you have the correct chain tension tighten up the spindle nut to the correct torque, and then make sure the lock nuts on the adjusters are tight. A too-tight chain is as bad as too-loose one.

10 Lube and go

Give the lovely new sprocket set a good start to its life by evenly applying a good quality chain lube to both the outside and underside of the chain, spin the wheel as you apply it to give the chain an even coating. It’s wise to fit a new chain when you replace your sprockets, so check out next week’s MCN to find out how.