Valve clearances !! Take the top rocker cover off , get feeler gauges ! Find a ten thou feeler , put a socket on the bottom crank nut , look for the rocker that is lowest down !! Count upto nine and insert the feeler under the rocker arm!! Adjust the gap until feeler slides nice and snugly!! Do all eight valves slowly and carefully !! If in doubt double check all clearances !! Put the le Iid on using a smear of sealant !! Do this while the engine is cold !! Done correctly the engine should be nice and quiet ! And smooth running !!
Good luck .