I hav a 86 f250 4x4 with a 79 400 in it.Along with a rv cam,edel 600cfm,headers flow masters 410 gears.I think its a nice set up lots of torque.My question is ever since Ive had truck when you get between 3500 to 4000 rpms it bends push rods.When I had trans rebuilt they had it on a lift @1200 rpm it was bending them.My mech. says the reason is cause of being modified.He thinks cro molly Pushrods will fix this.What do yall think could cause this and will cro molly fix it thanks for any feed back.
From the way you posted your question I would guess that you did not make the modifications to the engine yourself, they were done by the previous owner. Most "RV" style cams have a higher lift with a bit shorter duration to boost that low end torque. If the valve springs were not matched to the cam then they may be binding at full lift. At lower RPM's it would cause the push rods to flex at lower RPM's and then bend at higher RPM's. Chrome Molly may or may not fix your problems. Pop your valve covers and turn the engine over by hand and see if you can tell whether or not the springs are binding at full lift.
I have talking about this for a while now, and have not seen anyone who seems to have noticed it---
The 400's OEM and probably the 351M's for a number of years have had exaust valve rotators. I know for a plain, dead certain fact that they were on a 79 400 and caused the same problems. We (my brother) was very lucky that the last time, when he discovered it, he only bent an exaust valve head and did not pop it off in the cylinder.
He had OEM springs (equipted with rotators on the exaust) and had a crane cam with .500 lift, the worst part is that the work was done at a ford dealership in Orlando.
Exaust valve rotators replace the regular retainer and have a floating feature that allows the exaust valve to rotate with each cycle to help prevent certain hot spots on the seats and burning. They are also a lot thicker than the regular retainers. At normal OEM cam lifts, the spring still has enough compressed height to accomodate. When you increase the cam lobe lift, you soon reach coil bind. It was noted in the Crane literature, but the ford mechanics either didnt look or didnt care (prob didnt comprehend). My brother replaced the rotators with regular exaust retainers and went though the process of shimming the pedestals for the correct lifter pre-load. Seems the springs had enough installed height to work with the .500 lift. He did not say what max lift could be used and keep the rotators.
Maybe you already know about this, but if not, you sure should check! If this is the case, moly pushrods will only break other stuff-----and still bend! If you have intake pushrods bending also, you really need to check everything for coilbind. It would be a very simple matter for your mechanic to pull the valve covers and look for the rotators and even check for coil clearance at max lift. If he dosnt know what rotators are, you might want to drag it elsewhere LOL
Pop your valve covers and turn the engine over by hand and see if you can tell whether or not the springs are binding at full lift.
from the description, that it only happens when the rpms come up, or more accurately, WHEN THE OIL PRESSURE COMES UP, the coil bind will not present itself being turned over by hand. the lifter plungers will be down in their travel because no oil pressure is being supplied to pump the lifters up.
there's already enough evidence, it bends pushrods on a regular basis.
the solution is to either change the cam out for one that has a lift of .480" or less, or swap the valvesprings and retainers for aftermarket replacements that will allow higher the lift.
Stock intake valve springs go solid (coil bind) at 0.490" valve lift. The stock springs on early non-rotating exhaust valves allow the same lift as the stock intake valve springs, but the springs on the later rotating exhaust valves go solid at just 0.480" valve lift. That is less lift than many popular performance cams provide, even the milder ones like the Edelbrock #2172 (0.484/0.510 gross lift) and the Comp Cams 255DEH (0.469/0.505 gross lift). Using the stock rotating exhaust valve springs and retainers with either of those cams will cause bent push rods. "
grclark351--I agree, its not geometry. coil bind is coil bind, no matter what the angles are I had seen those lift figures before, just couldnt remember where. Given those figures, my brothers 400 just happened to have a little extra lift capability or the ford mechanics did put in new springs. The rotators were on the exausts and removing them and setting preload cure the problem. For some reason, the intake pushrods were not bending. Given the figures, they should have been bending, even without rotators----but they werent. Go figure . I forget what they called the cam (crane) but it was .500/.500, 110 ~270 deg at .050. Almost the same specs as the comp cams 270 Magnum. Really sounded good in that 400 and it was a "hoss". Probably not the right cam for that compression, but then we werent asked, the previous owner and the ford mechanics did it.
Just talked to mech. and he said he thought if lt was coil binding it would do it all the time this is about once a year thing.What if I bought new cam kit,push rods ,lifters etc,etc to a run together would this fix it.
RV cam don't really have that much lift that stock springs can't deal with it. I really think your push rods are too long, from decking the block, milling the heads, different installed valve spring height, or simply the wrong rods. Ford offers (or used to) different length pushrods to account for this.
Crane has shims for under the pedistals that will increase the clearance.
See what some of the others think, but I dont think I would throw more money at it. Somewhere you have a basic problem that you need to find. I still think it is coil bind. To bend a pushrod, you have to "pinch" it between the only 2 thing it touches, the rocker cup and the lifter cup. Did the lifter preload get checked/set? Some people think that a nonadjustable valvetrain can just be slapped back together----not so!
For some reason, there is not enough clearance between the 2, even if not all the time. Who knows, maybe a lifter pumped up or got trash in the valve, causing a few thousands of lesser clearance at rpm. Is it both pushrods, and does the exaust have rotators? With OEM pedestals and rockers, unless you took a lot off the heads via machining I dont see any way that geometry can do this. I am not saying it cant happen, just that I dont see it unless you have some aftermarket valvetrain parts.
it may not be coil bind per say, but possibly the retainers/rotators hitting the top of the valveguides, another critical measurement that needs to be checked before you slide an increased lift cam in an engine. it's a known red flag issue with 351M/400 heads, thus the "WARNING" by Bubba. "geometry" within tolerance limits in a non-adjustable valvetrain affects lifter preload and the rocker contact patch on the valvestem tip, pushrod length affects lifter preload and pedestal shimming affects contact patch and preload/pushrod length.
if the pushrod is so long that mechanical damage occurs, it's beyond "geometry" in my vocabulary.
first thing to do is check the lifter preload by prying between the rocker and retainer to compress the lifter plunger with a screwdriver and measuring the clearance between the rocker and valvestem tip. spec is .100"-.200" according to Tom Monroe p118. this is obviously with the lifter on the cam base circle, TDC firing position(compression stroke) will work. start with #1(drivers front) TDC firing position and do the 2 valves for each cylinder in the FIRING ORDER(13726548), turning the crank 90* each time. so you check #1, turn 90*, check #3, turn 90*, do #7, turn 90*...
if you find that you do not have at least .100" clearance between the rocker and valvestem tip, you can get shorter pushrods.
however, lifter preload should have no effect at full lift, but it's fun to check.
only 2 things i know of that bend pushrods; over-revving and mechanical interference.