I finally started the Bronco up again yesterday after months of sitting in the garage... back surgery and the need for a new fuel tank kept me sidelined for a while.

When I started it I noticed it was running rough and when I revved the engine it just seemed like something was "off". After tinking about it for a while and doing a little research I decided it was probably my lifters pumping up and holding a valve open. I decided this was a nice weekend project and removed a valve cover this morning, I discovered a rocker arm had been hitting the internal vent baffle of the valve cover and had worn down the corner of the rocker arm - bummer!

So I shimmed all the rocker arms another 0.030" and it really seemed to make a noticible difference. It's a lot colder now than when I last ran the engine, liek 45 degrees compared to 90, so the oil is quite a bit thicker. I may actually switch from my break-in oil - Chevron Supreme 10W30 with a Comp additive to a synthetic 5W20 and see what kind of a difference that makes.

This is my FOURTH attempt this evening to post, so I pictures will have to wait! I cleaned up the rocker arms - one each side and hammered a dimple in the baffle. Hopefully THAT won't happen again!

 

That's exactly the reason I've not powder-coated my valve covers yet. I have read about his problem and don't want to go to the trouble of PC'ing them and then find out they won't work. But glad you got it sorted.

 

Your lifters shouldn't pump up and hold a valve open unless you overrev the engine... however, if the rockers are adjusted just plain too tight and the lifter piston is bottomed out in the lifter, then that can happen at certain temperatures and/or all the time slightly... if you have any concern at all about lifters being too tight, I would suggest a compression test of all 8 cylinders to make sure the valves are all sealing tightly... running with leaky valves can burn a notch in the edges of valves and seats...