The chain and sprockets on your bike can withstand a lot of abuse, but they are far from invincible. In fact, they wear just as fast, if not faster, than any other mechanical part on your bike. When any one of the three key drive train components reaches its wear limit, bad things can happen. A chain that breaks or jumps off of the sprockets can easily snag on the countershaft sprocket (front sprocket) or lock up the rear wheel, ultimately causing severe damage to the bike. You may hear a slapping noise and feel some vibration, or in extreme cases you may even feel the chain skipping on the sprocket when your drive train components have had enough.
*IMPORTANT: If the time has come to replace any one of your drive train components--chain, countershaft sprocket or rear sprocket--I, like most others, recommend replacing them all.
REQUIRED TOOLS: Pliers and/or needle-nose pliers, ratchet and socket for rear wheel nut, Allen head socket for rear sprocket, closed-end wrench for rear sprocket, shop rag.
STEP 1: CHAIN REMOVAL
Locate the chain’s master link. Using a pair of pliers, pop off the master link clip by applying pressure between an arm on the clip’s open end and the adjacent chain pin. With the clip out of your way, remove the master link and your chain can be pulled off.
STEP 2: REAR WHEEL REMOVAL
Take the cotter pin out of the axle (if your axle has one) with a pair of pliers, and loosen the large axle nut with the appropriately-sized socket. At this point, I like to apply some upward pressure with my foot, which I place under the tire, in order to take the pressure off of the axle. The axle will now slide easily out of the wheel.
STEP 3: COUNTERSHAFT SPROCKET REMOVAL
Some bikes have a nut that must be removed first, but others, including the Suzuki RM-Z250 in the picture, require only the removal of a cotter pin. Use a pair of regular or needle-nose pliers and remove the pin. Pull the sprocket off of the shaft.
STEP 4: CHAIN WEAR INSPECTION
There are a few different methods for determining whether a chain needs to be replaced, but I find it quick and reliable to follow the procedure shown in the picture. Start by wrapping the chain around the rear sprocket. Hold the two ends of the chain with one hand and apply pressure away from the sprocket. With your free hand, pull the chain on the other side of the sprocket in the opposite direction. A chain that stays tight and does not lift too far off of the sprocket’s teeth is still in good shape. However, a chain that lifts far enough that you can see the top of the teeth on the sprocket is worn too much and must be replaced. It’s also a good idea at this time to check for damaged rollers and loose pins and links.
STEP 5: SPROCKET WEAR INSPECTION
Now it’s time to visually inspect the front and rear sprocket teeth for wear and damage. If the sprocket is missing teeth, it’s junk. If the sprocket is wearing to the point that you can visibly see the wear, it is time to replace it. Because of the torque, front sprockets tend to wear in the direction opposite of rotation. Conversely, the rear sprocket will wear in the direction of rotation. Worn teeth will look like waves and generally have a sharper point on the non-wear side.
STEP 6: REAR SPROCKET REMOVAL & REINSTALLATION
To make life a little easier, I use my 3/8 Makita impact driver with the appropriate Allen head when removing rear sprockets. If you don’t have one handy, a regular ratchet will also work here. With the appropriately-sized wrench on the inside nut, first break the nut loose slightly, and then you can completely loosen the Allen side. Remove all of the bolts and swap out the worn sprocket with the new one. When reinstalling the bolts, I recommend tightening them in a cross pattern to distribute equal pressure throughout the sprocket. Once all of the nuts are tight with my Makita, I alwways put an extra little tightening on the inside nuts with a wrench. Check your manual’s torque spec if you’re not comfortable guessing the appropriate tightness.
STEP 7: REAR WHEEL & CHAIN INSTALLATION
Reinstall the rear wheel using the opposite procedure that you used to pull it off. Before completely tightening the rear axle nut, however, check that your chain has the proper tension. I recommend about two to two and a half inches between the top of the swingarm and the bottom of the chain, just behind the chain guide. I use three fingers because they happen to add up to two inches. To ensure that the rear wheel is pressed up against the chain tension bolts, roll a shop rag back in between the sprocket and the chain (check out the next photo).
STEP 8: TORQUE REAR WHEEL NUT
Check your owner’s manual for the proper torque spec, and tighten the rear axle nut back into place. Now, lube your chain and go ride!