I have Craftsman 917.388740 self-propelled mower that has lasted more than 20 years with no repairs other than 1 carburetor replacememt, a few blades & oil. It has cast iron cylinder & I don't want to replace it til engine dies. My problem: Original drive belt stretched & no longer had enough tension even with adjustment to move wheels. Sears online & phone parts, as will as other online parts stores, no longer show drive mechanism on their parts diagrams or list a belt. So don't know what size belt to get. Took old belt to shop & they sold me new belt a little shorter (for $20!) which I installed & used adjusting knob on drive lever. Now it takes off at high speed with lever in off position. Removed corrosion & polished inner surface of drive pulley. Took lever mechanism apart to make sure cable travels full amount & lubricated cable which slides easily. Reassembled & problem persist. Does anybody know correct belt size for this model or have other recommendations?