Anatomy of an ATV: Drive Chain and Sprockets
Commonly Located: An ATV has two sprockets; both located on the same side of the ATV. The drive chain is wrapped around each of the two sprockets. A smaller sprocket sits in the front of the drive chain, attached to the engine transmission assembly. The rear sprocket is much larger and sits toward the back of the ATV in the back of the drive chain. The rear sprocket is attached to the rear axle assembly. Note that not every ATV has a drive chain and sprockets. This is an assembly that mostly appears on sport quads and older 4x4s. Most modern 4x4s do not have a drive chain or sprockets.
Physical Description: The drive chain is a chain similar in appearance to a standard bike chain. While most drive chains are identical, there is a difference between a chain with a master link (which can be removed for installation) and chains without a master link. Different installation methods are required for each type of chain. Chain can also be differentiated by the pitch of the chain links. For example, 520 chain is a common chain pitch. The chain length can also vary from ATV depending on make and model and is usually expressed in the number of links. For example, a stock KFX 400 uses 520 chain with a length of 112 links. Upgrading to aftermarket sprockets can also affect chain length.
Sprockets are all very similar in appearance, although they may vary by size and color. (Generally aluminum is the color of aluminum and forged steel is black). Sprockets are all round disks with teeth surrounding the outside. The front sprocket is significantly smaller than the rear sprocket.
Functions: As the engine turns over, the transmission causes the front sprocket to rotate. As the front sprocket turns, it pulls the drive chain. The drive chain pulls the rear sprocket, which causes the rear axle to turn, rotating the wheels and pulling the ATV forward.
Maintenance Costs: The maintenance costs for a drive chain and sprocket will vary depending on the quality of the replacement parts. Performance sprockets in a larger size and a lighter weight material will run higher than standard OEM size steel sprockets. Due to the way that the three parts interact (the drive chain and two sprockets), it’s not recommended to replace one part without replacing the others at the same time. Unfortunately, this does add to the cost of replacement. The drive chain and sprockets are not common wear items and therefore do not need to be replaced frequently. As always, the exception this is when there is heavy use and/or abuse. For an example, see our post called the Maintenance Bug for a run down of replacing the drive chain and sprockets on our Warrior 350.