ARGH!!

I was attempting to drive my freshly restored 76 F150 4x4 with a newly rebuilt (less than 500 miles) 390 from Washington to Arizona. Made it about 200 miles and that old familiar sound (that I'd heard in a previous motor) started. Bent push rod!
Funny thing is that while my Dad had it and was driving it around to test things out he bent 2 as well (and a broken exhaust valve spring) on the passenger side. He replaced them and all was well until this one bent, which was on the other side of the motor.
I haven't yet torn it down, but am fishing for ideas on what could cause push rods to bend? I'm thinking too tight of valve guide clearance, a "sticky" lifter that pumps up but doesn't release, but both are just guesses.

The heads were redone along with everything else...new cam, lifters, valve job, etc..
Would appreciate any ideas.

 

What kind of lift is on the cam, is there evidence of valve to piston hitting, Something is very wrong, did you mill the head and block? High compression pistons? Timing chain on time, did you use a degree wheel or straight up? double springs? Just to get the webs out of our brains!!!

 

Very good questions for which I wish I had answers. Long story short, the person who did all of the engine work has since retired and disappeared. He was an old friend and someone who had did engine work professionally for probably 40 years.
I have the cam spec's (at home), but it was simply a mild RV cam, with "normal" pistons, etc. Nothing high performance per say, so I wouldn't think a lot of out of the ordinary during the course of an engine rebuild was done.
I hope to pull the heads this weekend to see what I'm up against. I'm assuming no valve to piston contact at this point, and think I have a stuck/bent valve.
Keep in mind none of the pushrods bent immediately as I would have expected if any of the conditions of your questions had occurred. All activity occurred a roughly 200 - 250 mile intervals (2 bent pushrods and an exhaust valve spring failure at roughly 200 miles, and a second bent pushrod on the opposite side of the motor about 250 miles later).
Thanks for your reply and am open to any ideas. As I get things torn down I'm sure I'll have more questions, but anything to point me in the right direction as far as what to look for I'd appreciate it.
Thanks again!

 

You might also check fot upper end oiling. Are the rocker arms starting to bind or gaul? Only a tear down I'm afraid will answer and correct the problem. You need to check that the oiling bolt, one each side is in the proper position and that the rockers were properly re-assembled. Every piece has a proper order in which to be re-installed.

 

I think there's length options,? might have the wrong length

 

+1 i agree probably wrong length or reusing old worn push rods

 

or worse inexpensive New Chinese made push rods

 

Wrong length and Chinese would be the ultimate Fubar.

 

If the pushrods were too long, wouldn't they bend quickly? They were indeed new, but I have no idea of the manufacture's origin. Any suggestions for a reputable brand of push rod?

 

The only guess I would have is, the hydraulic type lifters are trying to make up the difference in length but come up short now & then.

 

This may help. FE's That Bend Push-rods, A Dirty little Secret | Ford Trucks

 

Thanks. I had found that article and will run through the process over the weekend.

 

finally got it pulled apart and found another broken exhaust valve spring on the number 3 cylinder. Think the other one was on #7.
I'll have the heads checked for proper valve guide clearance as well as ensuring the spring heights are what they're supposed to be for the cam that's in the motor.
After reading several articles, I'm almost convinced that not having the proper length pushrods may be the culprit (particularly by noticing that the valve stem lengths appear to vary slightly).
Question - the procedure referenced in the "...Dirty Little Secret" article states to bleed the lifters down. It seems there is a tool for this - does anyone know where to get one? Is there another method that would work using common tools?
Conversely (and given that there's only ± 500 miles on the motor) could I simply put a new batch of lifters in (unprimed), and then measure the valve lash to ensure I have the right pushrod lengths for each valve? Once completed, prime each new lifter, insert proper pushrod into each, and tighten down the rocker assembly?

Thanks again for any further help!

 

looks like I'm in uncharted waters. Will report back once I get it back together.

 

Had the same thing happen years ago, machine shop that did the heads had the guide clearance to tight they said after I took the heads back for a check.