Hey Guys!
I've got a 390 that we rebuilt with a Crane Energizer cam (pretty mild street grind). In it's first 300 miles, it has bent 3 valve pushrods. I can replace the pushrod, and everything is fine. Then in a hundred miles or so, it'll start missing, and I can pull the right valve cover, and find another bent pushrod on a different cylinder. I'd like your opinions; am I just finding the weak ones, or is there something else wrong.
It's really strong, and hard to keep your foot out of the 4 barrel. Has a low rear end, and so I could possibly be letting it wrap-up too far under hard acceleration.
I'm sure the valves are still OK, as it is extremely smooth under full throttle. And all the affected cylinders have good compression. I thought maybe some of the pushrods had been too long, or short, but they are all the same length.
I worked as a grease monkey at our local Ford dealership in the early 70's, and I can remember the mechanics changing a single pushrod more than once. Anyway, I'd like to hear what someone who is really really-up-on-it thinks.
As always; thanks for your help! I trust your opinions more than anybody else's.
Thanks, Brett

 

Find a repair manual, and do the valve-lash procedure. Sounds like you are using pushrods that are too long. If the heads were "done", and the valve stems weren't cut, the valves sit further down into the valve seat, and the stem sticks up too far, so there isn't enough valve-lash. Using standard-size pushrods, they will bend over time.

Ford used to have under/over-size pushrods, .060" over and under, I believe, and possibly even other sizes.

 

It sounds to me that you are running into the realm of valve float and may need stiffer springs on all of the valves. If you are floating the valves the pushrod(s) can get pinched at the rocker and as that causes an odd angled pressure on the rod it could cause it to bend, just slightly the first time but once it starts to bend it will continue to bend until the valve no longer operates in sync with the rest of the engine. Stronger springs may stop the problem. What rpm are you running the engine to? Please don't say you don't have a tach on it!