Here's the story.. 99 F250 auto 4x4 5.4L, Has miss in Cyl#2. Leakdown showed blowby on intake valve, take rocker off, no leakdown. Have since replaced.. Lash adjuster, Rocker, and Valve spring. Ran Seafoam through intake system to clean valves. I also took a brand new Lash Adj and machined .040" off the bottom and it rattled like crazy (too much lash). When I took the machined Lash Adj out it was pumped up and I measured it (50mm), A brand new Lash Adj is 51mm extended and will compress to 49.4mm. It sounds to me that a new lash adj is well within the rang of adjustment I need but for some reason it always hangs the valve open! I tried to measure the valve to see if it was sticking up farther than the others but there is no good reference point but it looked the same. While I had the valve off I took it through the action and rotated it and it wasn't sticky and there was no looseness in the guide. As I kept reseating it though the Leakdown became less and less, partially from the oil being pushed past the rings and partially from the valve sealing worse each time (I can't pull 100#'s of seat pressure) I was wondering if carbon around the seat could be hanging the valve up? I have let it sit for 2 days now.. will the lash adjuster bleed off.. Can I bleed it down somehow? I am going to do another leakdown on it tonight and see if it has sealed. I'm out of tricks and going out of my mind! Any help or ideas would be greatly appreciated.

 

Sounds like a bent valve. Whats the percentage leaking by the intake valve?

 

Bent/Warped valve, cracked or bad seat. I would just pull the head off.

 

With the rocker on it's 85% leakdown, take the rocker off and it's 6% leakdown. The lash adjuster seems like it has enough travel to take up the extra length if the valve is tuliped. I dunno, I'm totally stumped and do not want to take the head off if at all possible! Thanks
Nathan

 

You can live with 6% at the valve.
Sound like the lash adjuster or rocker is holding the valve opened as you suspected.
Is there any damage inside the head in the lash adjuster hole - is the pushrod damaged?

 

Well, I removed the head last night and found the problem. The valve in #2 was tuliped..bad.. to the point I could see the diff. That explains it. And on top of that, #2 had a plug insert in it and it was threaded itself out and smacked the piston, put a small ding in the piston, but no hole, thank goodness! Well, I get to buy some more new parts and get this puppy back together! Thanks for all the help guys.

Nathan

 

Sounds like the valve got hung up on the insert causing it to bend.

 

I think the insert came out after I changed the plugs because the last time I went to do a leakdown on it I couldn't get the leakdown tester to start. The valve isn't bent side to side it's just the head is stretched down. The valve seat sealing pattern is good and it would seal with the rocker off it was just a little too long with the rocker on and hung open. I think it might have been a bad valve or got hot and stretched. Hopefully after I am done swearing and re-installing the head all will be fixed and forgotten. I just put a torque converter in it 3 weeks ago! I think I can learn to love this truck after I take everything apart and curse it up and down!