You need to pull the head and inspect cylinder walls, ive seen a valve head get broken off and go right thru the side of cylinder wall, repair is not to difficult, removed intake , removed exhaust, pull head, replace valves and reseat valves seals etc, you can do 1 head only and repair but high mileage use you should do both , replaced broken plastic guide rails , roll in new chain, crimp or clip, retime engine, just basic info, get estimate or try and find good used engine