I just picked up a very cheap 97 F150. After driving it I noticed a misfire so i changed the plugs. All the plugs looked good other than #8 was black. A compression test revealed zero compression on that cylinder so I pulled the valve cover. The rocker arm had fallen off so I loosened off the camshaft and slid the rocker back in and torqued the cam down and put everything back together. When I fired up the engine it sounded like the valve hitting the piston. I am assuming there is a bent valve and that is likely the reaon for the rocker coming off. Any other suggestions or oipinions?