The key to long sprocket and chain life is to keep your motorcycle chain clean, well lubricated and properly adjusted. But even with meticulous maintenance, the chain eventually wears, and that causes the two sprockets to wear as well. And once one sprocket shows wear, it's best to replace the chain and both sprockets at the same time.
By the DIY experts of The Family Handyman Magazine
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A full day
Start at the drive sprocket nut
Photo 1: Loosen the sprocket nut
Snap a deep socket onto a 1/2-in.-drive breaker bar and loosen the drive sprocket nut. If the rear wheel turns, have a friend sit on the bike to provide resistance.
Photo 2: Raise the bike
Roll a motorcycle jack under the bike and locate the jack pads so they contact the engine and transmission, not the exhaust pipes. If the pipes are in the way, place short wood blocks on the pads to increase clearance. Then jack up the bike.
Remove the transmission cover to gain access to the drive sprocket and nut. The nut is often held in place with metal tabs, so bend the tabs down before trying to loosen the nut. Then, with the rear wheel on the ground, loosen the nut with a breaker bar and socket (Photo 1).
Next, raise and support the bike using the bike’s builtin stand, blocks and jack stands, or a motorcycle jack (Photo 2). A motorcycle jack is safest because it provides the best side-to-side stability. (The jack shown, No. 61632, is available at harborfreight.com).
How do you know when to replace components?
Chains stretch as they wear, and all bikes include an adjustment mechanism to take up the slack. Once you reach the maximum adjustment point, it’s time to replace the chain.
To check for sprocket wear, examine the top portion of each tooth and the valley between the sprocket teeth. The top of each tooth should be flat, and the valley should be U-shaped and symmetrical. On a worn sprocket, the top of the tooth wears to a sharp point and the valley becomes elongated on the thrust side. If you notice edge wear at the top of the tooth or elongation, it’s time to replace the sprockets.
Remove and replace the components
Photo 3: Relieve chain tension
Put a socket or wrench on the axle nut and loosen it. Then unscrew the chain-tensioning bolt, raise the adjuster and push the rear wheel completely forward in the slotted swing arm.
Photo 4: Disassemble the master link
Locate the clip opening and force it over the pin. Then remove the clip and the outer plate and push the pins out of the link.
Photo 5: Break the chain
Select an extractor pin to match the pin size of your chain and screw it into the body bolt. Secure the breaking tool directly over a chain pin and tighten the body bolt. Force the chain pin out of the link and through the anvil hole by tightening the extractor pin.
Figure A: Disconnect the drum brake
Loosen the brake-adjusting nut and remove the mechanical linkage from the drum brake. Then unbolt the brake ‘stay.’
Photo 6: Replace the sprockets
Bend the retaining tabs down and remove the sprocket bolts. Then swap in the new sprocket and tighten the bolts using a torque wrench. Bend the tabs up and against the bolt flats.
Relieve the chain tension by loosening the chain adjusting bolt and the rear axle nut. Then push the rear wheel forward and remove the chain (Photo 3).
If the chain has a master link, remove the clip with a pair of pliers and disassemble the chain (Photo 4). If your chain doesn’t have a master link, you’ll need a chainbreaking tool (such as the Heavy Duty Chain Breaker, No. 66488 at harborfreight.com). Mount the tool and break the chain (Photo 5). Then discard the old chain.
Next, disconnect the rear drum brake linkage and the stay (Figure A). If your bike has disc brakes, remove the caliper.
Slide the rear axle out and remove the rear wheel and brake assembly. Place the wheel on a workbench and replace the rear sprocket (Photo 6). Then replace the drive sprocket on the transmission.
Reassemble and adjust the chain
Photo 7: Install the master link
Slide the master link pins into the chain ends. Then install the outer plate and clip.
Photo 8: Align the rear wheel
Using the adjusting bolts, move the rear wheel in or out until the adjuster marks point to the same number of notches on both swing arms. That aligns the rear wheel sprocket to the front sprocket so it isn’t cocked. Rotate the wheel several times to fully seat the chain and check alignment and tension again. Adjust if necessary. Then tighten the locking nut.
Install the rear wheel, axle and brake assembly on the bike. Push the rear wheel all the way forward in the swing arm. Snug the axle nut slightly to hold it in that position. Then roll the new chain around the drive sprocket and onto the rear sprocket with the open link located near the top of the rear sprocket. Install the master link (Photo 7).
Next, tighten the chain-adjusting bolts to obtain 1-in. up/down play on the bottom portion of the chain. Err on the side of too loose rather than too tight (a tight chain causes rapid wear). Then true up the rear wheel (Photo 8). Tighten the axle nut to spec using a torque wrench and insert the cotter key (where applicable). Torque the drive sprocket nut to spec (rear wheel on the ground) and bend the tabs against the flats of the nut. Reinstall the transmission covers.
Beware of low-cost parts
As in other industries, the motorcycle parts market is flooded with substandard imitations and counterfeit name brand parts that don’t come close to the original manufacturers’ specifications. That’s why it’s best to buy parts from an authorized dealer or a trusted repair shop. If you shop online, check out the seller’s reviews first. An exceptionally low price on a name brand part is a red flag that the part may be a fake.
Lube and go
Lubricate the chain with spray chain lube and rotate the wheel several times to work it into the links. Then drive the bike slowly to fling off the excess before you hit the gas.