hey guys i have a 1990 f150 with a 4.9 i have rebuilt the top end now from the head up its a new head new lifters new rockers new pushrods new valves new valve springs and i have bent 4 sets of pushrods with only 300 miles on the rebuild valves re set right every time it runs great for a day or 2 then start it up and ill be running on 3 cylinders because of bent pushrods i have put 4 sets and it happens on 1 3 6 intake puushrods every time i have heard something about the injectors not working right and te cylinders not firing something like hydrolock is this possible because im lost now have put over a 1000 bucks in this thing with less then 300 miles on the top end.

 

- If you hydrolock an engine it typically bends the rods.
- If half (or all) of your fuel injectors were stuck open it still wouldn't be enough fuel to hydrolock the engine unless both valves were stuck closed.

I can't otherwise come up with a root cause to your problem, but figured I'd provide a little insight.

 

If it were hydrolocked, fuel should pour out when you pull those plugs. The SD EFI system on the 4.9 fires injs. 1, 3, 5. Pull the injectors for those cylinders. See if you can blow air both ends of the injector. That's how I diagnosis mine. It ohmed out fine though.

Is there anything else the truck shows symptoms of bending pushrods before it does it? How's oil pressure, compression, installed valve height, lifter manufacturer, heads shaved, what timing gear set is installed?

 

its a brand new head and it hasnt been shaved and it did it with the old stock head as well and ive tride to different sizesof pushrods as well and the timing gear is stock and never been looked at but if it was chipped or sheered the timing would be off and its not like i said it runs beautifuly the first day then like crap the next time you start almost like it happens over night or when you kill it and i just took anotgher look at it and 1345 intake are all bent and it cant be the cam or else it wouldnt run right in the first place right? and or the distributor gear. but even if it started a misfire that wuldnt cause the pushrods to bend would it? and those three pulgs 136 are fouled everythy time

 

Are you sure you have the correct valve springs on it? If you have some sort of "performance" spring on there it may not be able to compress as much as needed.. Are the coils of the spring really close when the intake valve is open? They should not be looking like there is no space when compressed.

It sounds to me like there might be some valve spring binding going on, also, are you using the rubber umbrella valve stem seals or the metal type? If the metal type are they tall enough to hit the spring retainer?

 

yes the springs have a sufficient ammount of gap between themand pretty sure its got the rubber seals but it still did it before with the old head this truck has only got 74,000 miles and 300 on the rebuild

 

Did you change out the lifters when you did the head? If not maybe you have some gummed up lifters that are building up (acting as a solid lifter) and causing too much lift, since it did it before the rebuild.

As was said before. if it were an injector (even filling the cyl completely full of fuel) you would bend a rod or break a piston, not bend a valve pushrod.

So you are left with a lifter going too high for whatever reason, or a valve that can't compress like it should for the amount of lift from the cam.

 

the lifters are brand new andther all pumping up and bleeding out how there suppost to there isnt 2 different sizes is there? because in order to torque the rockers down you have to completely bottom the lifter

 

Well, something ain't right.. The lifter should compress some, but it should NOT bottom out.. If they do, then when they pump up any at all thats when the push rods bend..

 

should i try setting my valves (torquing the rockers) with the lifters pumped because the chilton book says to use a lifter bleed down tool and completly bottom the lifters than a tdc 1 torque intake and exhaust then tdc 2 do 2 intake and exhaust then tdc3 then do 3 then comeback around to tdc1 and do 6 then tdc2 then do 5 then tdc3 do 4

 

HUH? That makes no sense. My translation is that your manual tells you to bottom the lifters then tighten some more?

 

Ya know, I gotta put my 0.02 USD worth in the ring.

The Haynes manual says 17 - 23 ft/lbs of torque on the non-adjustable sled (fulcrum) rockers. Didn't say a thing about rotating it around to do each hole because the lash is fixed.

Something aint right here. As far as collapsing each lifter, that isn't needed. My thoughts would be that the pushrods aren't the right length or the valvesprings do not match specifications. the springs may be going into coil bind at full lift, causing the bent pushrods. If the stands for the rocfkers were worn, they would increase the lash, which is opposite of what the problem is.

Gah, this is one of those times I wish I had that engine right in front of me to do a full diagnosis . . . I love a mystery.

This statement bothers me - has a part been introduced to this motor that is way out of spec? Like pushrods? The nominal OAL for that pushrod set should be 10.14" but they could be different lengths. See next paragraph.

Now, when it is stated to collapse the lifter, that's to measure the lash (gap) at the rocker tip. Specs say 0.125" to 01.175" with the lifter fully collapsed on the heel of the cam. Too little gap - get a shorter pushrod. Too much gap - get a longer pushrod. That range ensures the lifter is properly preloaded. I'm suspecting the gap is too little, causing the bent pushrods. If all is right, you just put the rockers in place and torque them down.

Just my thoughts.

Ray

 

If you had the same problem before replacing the head the issue would seem to be in another area.

Timing is a fairly common reason for bent pushrods. Just because it runs decent doesn't mean the timing is correct. I've seen engines with the timing way off run ok.

Did you find tdc compression by the piston and valve positions or with the dampner, or by feeling compression and then checking the piston position, or by feeling compression and then using the dampner?

The reason I ask if that if you used the dampner it may have spun which would put the timing off. Also, there is a notch in the dampner that is not the timing mark, the timing mark is a very small hard to see scribed line.

If everything is correct the position of the piston and valve train and the dampner should all agree. If they don't there is a problem.

As mentioned in the previous post all you should need to do is torque the rockers down to 17 to 23 ft/lbs. The other procedure is to check lifter preload and should not be an issue with all new components unless your cam is worn.

I suppose its possible a very worn cam could allow a push rod to pop out and get bent, but I would think it would have to be very worn to allow that. Not even sure its possible.

The Haynes manual has the directions for both older and newer style 300's so you have to make sure you are following the correct ones.

That manual, if I remember correctly also shows two locations for the #1 terminal on the distributor cap the older one and the one for your engine. It really shouldn't matter since the firing order is still the same, but at this point I would be very particular about making sure all the timing components are dead on the way they should be.

Another thought is your oil pump. Do you have good oil pressure? If its not the timing perhaps the valve guides aren't getting enough oil and are sticking when they get hot.

 

That was the key thing I was just going to focus on. He indicates that all this started because of the exact same problem he's continuing to have, bent pushrods. Given that, blaming the problem on the new parts seems like an incorrect path to be headed down.

 

The OP stated that he has not checked crank to cam timing. That would be something to look at.

I also think it's time to check to see if TDC really is TDC. The ring on the balancer could have spun, as stated by bdelmar2 and I do remember working on a 240 that had a very faint timing mark. Had to get out the white model paint to highlight it.

I'm less inclined to agree with valve guides seizing up, since that would be more likely to happen while driving, not after cooling off. This condition would have changed with a new head being installed.

I think I would go with first checking cam timing, then balancer for true TDC, then valve lash to make sure they are a minimum 0.125".

Just my thoughts, YMMV.