I was mowing neighbors lawn and hit an object I think to be wood. Mower immediately died, but started up again after a while. Blade looked bent so I replaced it. After doing so, I noticed the module for front propeller looked lose. Then after moving it, noticed that it was what tightens the belt and propels the mower. How do I tighten that belt, as it seems to slip when starting and does not have the propeller speed it once used to have, This mower is only one year old. Craftsman front propelled mower model # 917370680. Thanks for your help. - Michelle