How to renew the chain and sprockets on the Yamaha Thundercat

You will need: good socket set, preferably half-inch drive, a torque wrench, a rear paddock stand, a good quality chain staking tool (you can hire these), an assistant (large).

First, buy your chain and sprockets. They are cheapest as a kit.

The chain type is 50ZVM, 108 links. DID and RK are both very good makes of chain. Chains should be O-ring or X-ring and come with a soft link that you rivet into place with a special tool. Avoid endless chains (you have to remove the swing arm to fit these) and chains joined with a spring clip, they are not safe.

JT sprockets are good and tough and Renthal make fancy coloured alloy ones if that’s your bag.

The standard gearing is 15 teeth at the front, 47 at the back. You can go down one tooth at the front to improve acceleration, or go up a couple at the back for a less drastic increase and better chain life.

Now to business. First you need to remove the front sprocket cover. Put the bike in neutral and remove the small pinch bolt that clamps the gear lever to its shaft and slide if off (there is a little dot to help you get it back in the right place). Remove the six allen-head bolts and pull off the sprocket cover. There is no need to detach the clutch cable. There is a paper gasket behind the cover. You can replace it or reuse it if you can salvage it, but you can get away without one at all.

The sprocket nut should have a tabbed lock-washer behind it, and you will need to bend the tabs out of the way before you can get your socket onto the nut. Ideally you would then use an impact wrench or air wrench to remove the nut. In the real world we don’t have such fancy tools and need a fat assistant instead.

Now get said rotund assistant to sit on the bike and press HARD on the back brake. This is to keep the wheel and chain still as you undo the sprocket nut. This nut will be very tight. If you can’t shift it try extending your wrench with a few feet of scaffold pole. Take care not to smash your knuckles. If it really won’t go, then admit defeat and get a dealer with an air wrench to remove it for you.

With the nut removed, simply slide the sprocket off the shaft, chain and all. Work the old sprocket out of the chain and stick in the new one. Replace the nut, and with your assistant still on the brake torque it up to 70 Nm (54 lbs-ft). If you have no torque wrench, do it up pretty damn tight, if this baby works loose things get ugly. Bend down the tabs on the lockwasher.

Next, the rear sprocket. You will need to remove the rear wheel to get to this. Loosen the rear axle nut slightly before putting the bike on the paddock stand. Slacken off both chain tension adjusters (in the ends of the swingarm). While supporting the weight of the wheel, remove the axle nut and pull out the axle. Lower the wheel to the ground and push the it forwards. Slip the chain off the sprocket and withdraw the wheel.

Undo the six nuts holding the sprocket onto the sprocket carrier, and change over the sprocket. This is easiest with the carrier still in the wheel. Torque up the nuts to 60 Nm (43 lbs-ft). While you are in there, pull off the carrier and check the cush drive rubbers and bearing are in good nick.

Refit the wheel, making sure one pad goes on each side of the disk. Put the axle back in but don’t tighten the nut yet.

Finally it’s time to change the chain. You can use your staking tool to split the old chain, but you risk damaging the nib and they are expensive. It’s better to use an angle grinder or a hacksaw to cut the old chain.

Now attach the new chain to the end of the old with some fine wire. Rotate the rear wheel to draw the new chain into place. Remove and discard the old chain.

Fit soft link into place to join the new chain, and use your staking tool to stake the rivets. They should be well peened over with a deep hole in the centre, but not so flat they crack or restrict movement of the link. If in any doubt get it checked at a garage. New links are only a fiver, but a broken chain can be very very ugly.

***Remember to grease the soft link with the grease provided before staking it ***

Finally, tension the new chain with the adjusters and torque up the rear axle nut to 117 Nm (90 lbs-ft) or very tight indeed. Give the front sprocket cover a quick clean out (with a spoon!?) and refit it. Reattach the gear lever.

That’s it!