cb450 interference?

tore into my 72 450 today to inspect the cams...
they have some very light wear no real scoreing but all the timing chain and sprockets look good
so i went ahead and pulled the head off because one side had 180 psi compression (cyl full of oil)
the other i was not able to read.
The threads on the spark plug hole are almost gone so i find that the side with the striped spark plug hole
(right side sitting on the bike)
intake valve was not fully seated so i wipe off the piston and found that it has made contact more that once.
the other 3 valves all look normal with no contact so where do i look for the problem?

valve spring weak? im new to torsion valve springs
valve lash adj.? shound not affect valve to pistion
over rev?
rod bearing or wrist pin play? then would it be intake and exhaust valves
valve keeper come loose and one point?
thanks,
ZIMM

If I had to guess the valve was stuck slight open and the piston struck the valve and bent the valve stem. I would check the valve guides. I would replace the valve and valve guide that you are having problems with as a minimum. And consider doing them all