the cam cover is top of the motor, with it running , feel the the top of the motor . specifically , there are 8 circles on the top of the motor , they have a 17mm bolt shape on top of them , these are the tappet covers, under these are the tappets, witch push the valves if you feel the knocking your talking about on the tappet covers, follow the link TT gave, in all honesty you should follow that link and set the tappets anyway , they need regular maintenance, and i'd be willing to bet they are off at least a little
hope that makes sense , i've had a few drinks already