the valve in question isnt opening all. there is about .18 inch slack between the pushrod and the rocker right now. i guess my real question is why do the parts store, haynes, and the local jeep dealer all disagree on the correct pushrod length? haynes says 9.64 to 9.66, parts store says 9.72, dealer says 9.69. and mine measures 9.53. also the parts man told me that pushrods can collapse, depending on what style they are.

Are you SURE it is not opening? If so take the spark out and close the gap completely.. Then reinstall and see if it runs better on 5 cyls. If your lobe is that worn you do need a new cam and lifter set. This will involve more work than you might wish to do however.
You must have someone turn the engine by hand to see how much the valve is opening.
I have never seen a situation like you describe that the lifter did not complain loudly.
At rest and the valve closed sometimes there can be slight amount of gap between the rocker and the valve/pushrod as the lifter has relaxed. However under pressure the gap quickly closes.. A feeler guage can be inserted between the valve stem and the rocker while ideling to see if opening the valve farther will help the idle.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

i ran the motor with the valve cover off. i assure you the valve isnt opening. if i hold down on the rocker above the pushrod i can feel the cam working just as good as the valve on the next cylinder. the rocker on the bad cylinder is floppy loose. the pushrod just picks up the back of it and doesnt push the valve down.

Ok then do this! Swap the rockers and their balls from ONE cyl to the next! See if that one now works or not! If YES then go get nother rocker and ball for where ever the bad one is now..
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

I just read through this post and I still have a few questions, Jim you will have to chime in here because I havenÆt taken my 4.0 apart yet, but are all the rockers on a common rail or do they have individual mount posts like a Chevy? If they are individual I would pull the rockers on the bad cylinder and see what the push rods look like. The only thing I am really curious about is, Is the valve on the ôlooseö rocker actually closing all the way? Have you done a compression test? I didnÆt see any numbers for what your compression was across all the cylinders. I would be really hesitant to mix and match used parts because as Jim said they will wear on each other faster because they are already worn in. Have you taken any pics of the head? Maybe something will jump out visually that you are not seeing.

Sean

Yep! The rockers are individualy mounted and easily swapped. I had not thought of a bent valve! Glad you happened on that. A quick measure of valve height would tell him quite a bit about that valve. They don't run worth a $hit with a bent valve.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

pictures are a good idea....but i cant find the cord that goes from my camera to the pc. as for the compression, i didnt check it. i borrowed a friends tester and the fittings didnt fit my spark hole and i havent been able to catch anyone free lately to turn the motor over while i hold the rubber tipped fitting. as for valve height, aparently the lifters leak down overnight. i dont know if this is normal or not. i measured the valves yesterday morning after it had sat all night. they all measured the same. i turned it over and they all measured different as they should.

i was loading corn all day so i didnt get the chance to work on the jeep. i guess my first move in the morning is to swap some rockers and rocker balls to see if that eliminates the slack. if not i think im going to pull the cam and measure the lift height of the lobes to see if there is any difference. if not im going to blame the lifters. do i absolutely have to replace the cam if i replace the lifters?

If you are going to pull the cam go get a new coolant pump, camshaft install gasket set,camshaft/lifter set and pushrods. I would expect to need new rockers and balls too.
So the last thing I would do is to think about a camshaft till I WAS CERTAIN I HAD to have one.
And YES you will need new lifters. A little known fact about lifters is they are NOT FLAT on the bottom! Put two new ones bottom to bottom and they will ROCK back and forth as the bottoms are rounded some.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

Yeah I wouldnt pull the cam until its the only possible things left that could be wrong. I would do more trouble shooting up top first. I dont think the lifters should leak down over night either, they might loose a little, but to go all the way down, i doubt that. If they do leak down it with click and tick for about the first 20-30 seconds until the lifter pump back the little they lost. You can do another way to measure the cam with out pulling the cam too, if you tak all the rockers off and keep them in order and check out all the push rods are in good shape and dont find anything (again keeping them in order), make sure the lifters all have recently has pressure on them, and one at a time put in a push rod and hold a dial indicater on the end of the rod and have someone turn the engine over by hand. this will be easier to do with the spark plugs out. Granted this will not be as good as measuring the cam directly, but it will require a lot less remove and replace work than actually pulling the cam. Just take your time and hit each out down the line.

Sean

havent made it to the shop yet. but im still curious about one question that hasnt been answered yet. how long are my push rods supposed to be?