How to replace a chain and sprockets
A bike’s chain and sprockets are prone to wear and tear because they are: a) exposed to the elements, as well as the effects of grit, dust, surface water, or all three b) often insufficiently lubricated, and c) stretched and compressed every time the throttle is opened and closed. Wear is exaggerated if the chain is too loose or too tight. Wait until it’s hanging on the floor, or riding over non-existent sprocket teeth before replacing them and you’re playing with fire. Sooner or later the chain will break or fly off the sprockets, causing engine damage – or much worse – as the chain wraps itself around the rear wheel or drive sprocket and locks the bike up.
What you’ll be dealing with
Two sprockets and one drive chain designed to transmit engine power to the rear wheel.
Don’t think about it if…
…Dirt, grease and scuffed knuckles aren’t your cup of tea, and you’re not confident about tackling something your life depends on.
Stuff you’ll need
A paddock stand (if your bike has no centrestand), a half-inch drive socket set (10-19mm minimum), a socket to suit the rear wheel spindle nut and a torque wrench. Combination spanners (ideally 8-19mm), copper grease, Allen keys (4-10mm), molegrips and a couple of hefty hammers to rivet the chain’s joining link. A chain splitter tool or mini-disc grinder would be good – as would a friend to help.
What can go wrong?
If the rivet link isn’t fitted correctly the chain will fly apart. Or you might leave a spacer out of the rear wheel assembly!
What skills do I need?
It’s easier than replacing the crankcases, which is what you’ll be doing if your chain and sprockets deteriorate.
1. Scrutinise the new parts. Look at the owner’s handbook to check the sprockets have the same amount of teeth it states, and the chain is the right length (correct number of links). Also check the chain is the right pitch (distance between each teeth and width). Every other link is usually marked with the pitch, eg 525, 420 etc.
2. Place the bike on a rear paddock stand – the rear wheel needs to be clear of the ground for removal later – and remove the front sprocket cover. Keep it safe and out of the way making sure no locating dowels are dropped. It’s also a good idea to remove the build-up of any chain lube that’s been flung off and stuck to it.
3. Loosen the front sprocket retaining nuts, or nuts, and splined retaining plate. If it’s one large Nyloc nut you’ll need to hold the sprocket still or it will turn. With the bike in gear get someone to hold the rear brake on, or place a chock (ideally a block of wood) between the rear sprocket and chain to stop the driveline from turning.
4. Now loosen the rear sprocket retaining nuts that are easily accessible, again using a chock to stop the wheel turning. These buggers can be tight so use a long-handled ratchet/socket T-bar. Remove the chock to turn the wheel to get at the nuts behind the swingarm then replace the chock.
5. If you’ve got a chain breaker use it now on a link in the lower chain run. If you can’t get hold of one use a mini-grinder. Place wet cloth on areas of the bike that might get showered with sparks. Grind off the rivet heads and use a punch or a small nail to push the rest of the links from the remainder of the chain.
6. With the bike in neutral and the chock removed carefully pull one end of the broken chain away towards the back of the bike – the rear wheel and front sprocket will turn to allow this. Bin the old chain. Now take out the rear wheel and take off the rear then the front sprocket. Place them over the new sprockets to ensure they are the same.
7. Fit the new front sprocket on to the output shaft. If there were any spacers or shims (rubber coated metal spacers) put them back in the same order they came off. You can, if there are two small retaining bolts, tighten them up now. If it’s a singular centre nut wait until the new chain is on and chock it up. All bolts/nuts need to be torqued tight.
8. Fit the new rear sprocket on to its mounting studs. Fit the nuts and tighten each to the required torque in an opposed criss-cross order – top left, bottom right, etc – to ensure the sprocket is flush against the hub. Your dealer can supply all the torque figures for the complete job if you haven’t got a workshop manual. Now refit the rear wheel.
9. Fit the new chain so its ends meet on the rear sprocket. From the inside of the chain push the rivet link through the two ends – note fitment of O-rings according to the instructions. Put the rivet link plate over the protruding link pins and squeeze into place with Molegrips (or two 1/2in drive sockets over the pins, squeezed with a G-clamp).
10. Get a friend to hold a solid metal object (eg 2lb lump hammer) against the rear of the rivet link to absorb the force of you hitting the upper and lower edges of the split link’s pins. This flattening (riveting) of the pins stops the rivet link plate flying off. Don’t go too mad or you’ll crush the plate too hard against the O-rings.
11. Now chock the rear wheel again to tighten the front sprocket-retaining nut to the required torque (ask a dealer for the figure). Check no cables (speedo sensor) are in the way of the sprocket when it spins. Refit the front sprocket cover complete with locating dowels. Dab a little copper grease in the bolt hole threads.
12. Check everything is tight – just try nipping up the rear sprocket nuts again – and then adjust the chain as you would normally. New chains need tensioning within 300 miles because the packing/lubricating grease between the rollers gets forced out, leaving it slack. Lubricate the chain every 200 miles, or after it rains, to prolong its life.