engine knock

[zaconrad]

Hi everyone 

I have a 1990 jeep 4.0. It has a very bad slapping noise coming from the valve train. I've traces it to the number 6 cylinder. I know it's not bottom since I've taking the whole engine apart trying to find this issue. I ran the engine with out the valve cover and noticed that one of the pushrods is spinning a lot slower than all the rest. All the lifter have been replaced and it has a brand new cam with less than 100 miles on it. 

Anyone have ideas?

[TurboedMJ]

I guess check valve lash and if you have a feeler gauge check the clearance between the valve and the rod and compare it to the others. Also check clearance between piston and cylinder wall and make sure your piston ring gaps are correct. 

[zaconrad]

Iv done all of those I know it's not the piston. It goes away when you take the rocker off. I've checked lashe it's consistent with all the others. I just pulled the head and all the valve are straight and in good shape as far as I can tell.

[cruiser54]

Bent pushrod? 

[zaconrad]

No all the pushrods are straight. I also just swapped heads and the problem still persist.

[cruiser54]

You may have a collapsed lifter or a flat cam lobe then.