The 400EX is an all-terrain vehicle commonly called a 4-wheeler. The 400EX, manufactured by Honda, has a chain drive that connects the transmission and rear axle sprocket. As you ride the 4-wheeler, the chain starts to stretch. When this happens, you must tighten the chain. Fortunately, if you own a 400EX, the process is not very difficult and requires the use of basic tools.
Locate the four Allen bolts on the very back of the swing arm. The swing arm is the metal bracket that connects the frame of the 400EX to the rear axle.
Loosen all four Allen bolts with an Allen wrench. Do not remove the bolts just loosen them so you can rotate the axle carrier inside the swing arm.
Grip the axle carrier with a paint of channel locks. You can locate the axle carrier by looking between the sprocket and the swing arm. The carrier has a split through the center of it. If you do not have a pair of channel locks, you can edge a large flat-head screwdriver between the split in the axle carrier. However, using channel locks will prevent the carrier from breaking.
Rotate the channel locks towards the back of the ATV. This will tighten the chain. Stop rotating the axle carrier when you can press down on the top center of the chain approximately 1 ½-inches.
Tighten all four of the Allen bolts to lock the axle in place.
