'90 Ranger with a BAD clack. (long)

[74Rallye]

Usually a lifter makes a tic, but this one makes a clack! It's in a 1990 Ranger with a 2.9 V6. Here's the history:
4 yrs. ago it went to the shop for what appeared to be intermittent lifter problem. One of the heads was found to be cracked and both castings were replaced along with the lifters. The engine was also rebuilt at that time. The intermittent tic was still there and another new set of lifters was installed. The shop finally gave up.
The ticking is now a clack and it just keeps getting worse. Sometimes it goes away completely, only to return with a vengeance and a loss of power. The problem is valve train related. The noise is coming from under the valve cover on the driver's side. Oil pressure is good, the engine makes good power (when it's not ticking). The truck and engine have never been abused.
I need to fix this quickly. What I'm afraid of is that with the problem being intermittent, I could tear it down and not find the problem. It's as if the oil supply to one or more lifters is getting cut off.
Any suggestions would be appreciated!
Thanks.

 

[Rick]

The rocker arms can get badly worn on those motors. The cup where the pushrod seats becomes oversized and allows excessive clearance. The cup can eventually get so bad that the pushrod can punch through it.

 

[74Rallye]

Can rocker wear create an intermittent situation? Can the pushrod on a 2.9L V6 move around, out of the cup perhaps?
The engine will go from smooth to clacking and back to smooth without regard to running time or temperature.

 

[Rick]

Originally posted by 74Rallye
Can rocker wear create an intermittent situation? Can the pushrod on a 2.9L V6 move around, out of the cup perhaps?
The engine will go from smooth to clacking and back to smooth without regard to running time or temperature.

No it wouldn't be moving in and out of the cup. Rocker wear wouldn't be intermittent either. Sounds like the lifters internals could be sticking.

 

[74Rallye]

Hey Rick,
I would bet cash that it's a lifter problem if they had not been replaced twice without helping the situation. I wonder if the lifter bore could be cracked, intermittently letting the oil pressure escape?