I thought I would share a recent experience that resulted in a bent pushrod. I had the head and barrels off my 61 GF over xmas to replace the cam followers and to decoke it.
I actually discovered worn cam followers, burnt valve guides and the valves were pretty pitted too. The real surprise was the top compression ring that fell into 2 pieces when I was inspecting it!
I duly replaced the the rings, cam followers, four new valves, springs and guides and reassembled it and set the valve clearances. All going well so I turned the motor over by hand which felt strangely very restricted and tight. So off with rocker box only to find a very bent pushrod.
After a lot detective work Morse would have been proud of, it turned out that the somebody in the past 50 years or so had fitted 1950s Road Rocket alloy head valves at some point complete with their respective caps and collets. I had taken care to fit the correct parts for the year but my mistake was to use the old spring caps and collets. This resulted in the springs when fitted to proper GF valves becoming coil bound and something had to give when the valve opened and in this case it was a pushrod. Moral of the story, never assume because the bike appeared to be running ok before it was dismantled that it has the correct parts fitted. I learnt the hard way I'm just relieved I didn't try to start it up.
It's all back together now by the way and running like a dream. (Complete with Gold Flash spring caps and collets!)