Which means a possibly damaged valve...Would I be correct?
fungshwai,when the piston meets the valve, the valve is usually not damaged.
When the piston meets the valve, the rod of the pusher is usually bent.
So whether it can be found by removing the valve cover and inspecting the condition of the rods of the third cylinder. The bent barbars have a large clearance.
The bent rod can be pulled out of the mechanism without disassembling it, it is usually sufficient to unscrew the adjusting screws from the rocker arms.
After replacing the new or straighteners of the rods and installing them in place, you need to adjust the gaps in the timing mechanism.
But before removing the cover, you need to remove the third nozzle from the head of the unit, close the nozzle channel with a cork folded from paper or cloth, simply close it with your finger and do not turn on the fuel supply by cranking the crankshaft with the starter.
If the timing mechanism does not have any damage, the stopper will sharply fly out of the channel, the finger can not be held.
Then the cause of the failure of the third cylinder in another.
If the plug does not fly out or the finger can be held, then it is possible to remove the valve cover.