I replaced the walk belt on this Horizon CST3 Treadmill in Portland, Maine. The old walk belt folded over onto itself a was destroyed.
To do your own, first remove the end caps by removing the two screws underneath each cap. Then remove the rear roller bolts, and remove the rear roller.
Then remove the side rails. The key thing to remember on this walk belt replacement is that the side rails come off in two sections. The rear section of the side rail slides off the tail end.
Then you need to remove four screws in each side of the front sections of side rails to remove them. The two screws at the front end of each side rail are exposed after the motor cover is removed.
The hidden part is that you need to remove the plastic labels to expose the other two screws in each side of the side rails (see images below).
Then remove the front roller, noting the position of the alignment bolt.
Remove the four deck bolts along the edges on each side of the deck. Once these are removed, you can then remove the deck and walk belt from the treadmill. Slide off the old walk belt, and slide on the new one. Then reverse the procedure to reassemble.
Be sure to lube the deck and center the walk belt before you tighten up the belt. Tighten the walk belt evenly at the rear roller bolts until you can only lift up the walk belt on both sides, at the center of the belt, about two inches. Start the treadmill at its slowest speed to insure the belt stays centered. To move the belt to the left, tighten the right side a quarter turn at a time. To move the belt to the right, tighten the left bolt a quarter turn at a time.
Let it run for a few minutes at the slowest speed to insure the belt stays centered. Then speed the belt up to 2 or 3 miles per hour, fine tuning the adjustment as needed.
Once you let the treadmill run for a while to insure the walk belt is centered, then at a speed of 2 miles per hour and your left foot on the floor on the left side of the treadmill, near the walking position, which is near the front of the treadmill, stomp down of the walk belt in an attempt to stop the belt with your right foot.
You should be able to stop the belts, rollers and motor. Do not hold this for more than a couple of seconds. If the walk belt slips on the roller, then the walk belt is too loose. Tighten both rear roller bolts by ½ turn and try again. You want to adjust the walk belt tightness to the point where it no longer slips on the roller when you stomp down on it, and no tighter.
If you over tighten the walk belt it can cause excessive wear and shorten the life of the walk belt, roller bearings and other components.
On the other hand, if the drive belt is the belt that does the slipping, then either the drive belt needs to be tightened or replaced. The drive belt is tightened by loosening the motor hold-down bolts and moving the motor forward. Do not over tighten the drive belt. Usually moving the motor forward just ¼” is sufficient.