The motor drive belt is adjusted independently from the walking belt. Some newer models have an auto tensioner which is a lever that has a wheel that puts pressure on the drive belt and a spring on the other end that automatically loads the belt to the proper tension. You should not adjust these since they are preset. If the motor belt is slipping with this design, replace the motor belt.
Tension can be affected slightly by adjusting the tension of the walking belt but if you have a slipping problem, the drive belt will require replacement. If your drive belt is too loose, it will slip on the front roller pulley or the motor pulley. If it is too tight, it will increase your amp draw to the point that you may have an electronics or motor problem. Due to this, it is better to be on the safe side and replace a drive belt rather than risk over tightening it. A drive belt is usually $29.99 or less while many parts you can damage by over tightening can be more than $300. Additionally, too much tension can cause bearing failure in the motor and the front roller and front roller pulley failure. It is better to err on having the belt a little too tight rather than too loose due to the possibility of injury if the belt slips.
Some designs use a jack bolt where you can loosen the motor mount bolts and then push the motor away from the front roller. We only suggest a minimal adjustment on these designs and if a small adjustment doesn't help, replace the motor belt. Once again, it is easy to overtighten the belt and ruin other parts.
Many of the older Keys units did not have a good way to tighten the motor belt and you must use two people. One to use a pry bar in order to keep the proper tension on the belt and the other to tighten the bolts. Make sure to not put too much pressure on the belt once again to prevent overtightening.
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