Very hard to bend a valve on this engine, valve opening straight down, unless some thing
was under the valve when piston hit it.
The piston comes very close to the head, if a rod bearing is bad the piston can come in
contact with the head ,it is possible when oil is cold and thicker the clearance on rod
bearing will be taken up by the thicker oil, piston does not hit head, oil thins with heat
piston now hits. Just a possibility, but can happen.