392 heads bending pushrods but nothing looks wrong
I finally decided to rip the heads off my truck after becoming tired of it running on only 7 cylinders after the intake pushrod on #7 would bend and break.
Here is was my problem...
On my 5 mile trip to school and back it will run fine and not act up. But on my 20 or so miie trip to work and back it likes to have the intake valve stick, causing major backfire through the intake manifold causing a severe lack of power and is just plain annoying. After doing this enough times the pushrod seems to give up and break. I know this because my truck starts smoking because there is no gas to burn up the oil accumulating on the #7 spark plug. This has happened numerous times and I am getting sick and tired of it. I want to know what is going on.
Second problem: I pull the heads off and look at #7 intake valve because that is the only pushrod that has ever bent, and I keep replacing it, even installed a new lifter, but nothing seems to work. I took out the valve and there are no scuffing marks on the valve stem, in fact it looks perfectly good and usable.
What could possibly be going on in my engine to make it act like this?
Symptoms: Usually on highway traveling 60 MPH and I start to hear a popping sound, slowly builds up to where I can't give my engine too much throttle otherwise I will slow down very fast, this usually leaves me left going 45 MPH max. If I shut it down and let it cool for a while it will usually run normal again until it starts to stick.
Funny thing is I never had a problem in the 2 years I have owned it until last summer when on the way home from work it bent two pushrods, one on #7 intake and the exaust pushrod on the passengers side. I know I said that only #7 bent, but #7 is the only one that has bent more than once.
I am very annoyed at finding that #7 intake valve was ok, I guess it means one less expense but that would have explained the problem. Can anybody else think of anything? Would the intake valve not seating properly be a partial cause? I need help and would like to be able to drive to the coast and run on all 8 cylinders there and back for the rest of this 392's life.