pulled head on a 390 with 3 bent pusrods ( all intake, from each bank ) All valves fine, re did all guides , tested springs, , no binding, reassembled ran great for less than 100 miles, a bad miss, 2 different push rods bent (intake each bank ) spinning up oil pump (2000rpm) with lifters in, head on, intake off, rocker assembly off, oil pressure sits at 45psi, no spike to point to a bad oil pump valve, rocker shafts not scored, lifter / cam surface no were , flat lifter face, oil used GTX 10w30, never synthetic but changed regularly @5000miles

 

FE's That Bend Push-rods, A Dirty little Secret .: Articles

 

The "dirty little secret" is a procedure that was fallowed for 1st head replacment and gives no explanation or theory as to the reason for a untouched 390 bending 3 push rods after 50,000 well maintained miles.or a reason for the shorter life of replacements.
Note* All old push rods (3 straighten ) are the same length

 

Did you have the head's off ??

 

My one experience with bent pushrods was on a marine engine. Long story short it was not laid up correctly for winter. On spring startup it bent a couple of pushrods as a result of corrosion between the valve guide and head. Valves were effectivly frozen. I imagine inadequate valve to guide clearance could cause the same problem... the valve basically locks up when warm.

It required head re-build and new/used pushrods to get it going again.

 

YES ! Both (2) heads , one from each side of the motor ( engine ) had been , removed, taken off as described in " Ford's dirty little secret " in an attempt to diagnose the reason for the bent push rods on the well maintained , 50,000 mile motor, no burrs on stems, or any other damage as in valve / piston kissing, valve spring not binding, rocker arm shaft rolls straight, no ridges or burrs, replaced valve guides as long as the valves were out. Replaced bent push rods drove for less than 100 miles lightly and different push rods bent.
don't feel bad if this stumps you, Two prominent race engine builders , 1 car, 1 airplane, Napafix and a Ford Dealership have no ideas

 

The pistons aren't showing "witness" marks from valve to piston contact?

You sure the cam is correctly installed?

Are you tightening down the rocker shaft correctly?

Trying to spin the engine past 5000 rpm with an RV cam?

Josh

 

As mentioned , NO CONTACT OF VALVE TO PISTON
As mentioned, Installation proceduer was fallowed as Noted in " Ford dirty little secret"
As mentiond, the push rods bent after 50,000 well maintained miles,NO CAMSHAFT WAS CHANGED
As mentioned, LIGHTLY USED

 

Then worn exhaust cam lobes from using the wrong low zinc modern energy conserving engine oil, which causes excessive combustion pressures... which equals bent intake pushrods.

Use diesel oil from now on.

Josh

 

I had the same problem with my 300 I6 after setting in a barn for 18-22 years. The more I ran it, the more it bent push rods. I knew it was time for a rebuild. However, I don't know if this would apply to the OP, he has well maintained his engine for all these mile and suddenly bent push rods.

I remember a friend had this problem years ago, but he was putting large cams in his small block and running at high rpm's when it happened.

Please keep us posted on your findings, best of luck and maybe we can all learn something here.

 

old gas varnishing the valves causing bent pushrods

 

Have you ever actually checked each valve to see just how much preload is on each lifter ? Checking the way that article says does nothing as far as I'm concerened to set preload which at tdc on each valve should be IMO .020-.040. I've built more than a few FE motors over the years in my shop and always set preload the same as any other motor, a little different procedure with FE's but I'm only concerened with actual lifter preload = how much the push rod pushes the lifters plunger down at that cylinders TDC.

 

The lack of zinc = cam lobe wear is a good one, I think measuring cam lift at this time may be the next step, as I am looking for a existing problem , not a problem that occurred after assembly ie. pre loading lifters

 

Did you ever figure out what the root cause was?

 

I caused 3 or 4 pushrods to get bent in a 360 by fiddling with the distributor advance trying to correct what was actually an ECU issue. While driving, I experienced a significant "miss" just as you did. It ran much worse after that so I pulled the valve covers and discovered the bent pushrods.
Does any of that story align with your situation?