Can the lifters be successfully adjusted on the 4.0l OHV engine? My truck is a 2000 but had a rebuilt engine put in in 2005. The lifters are starting to tap at 87,000 miles.

 

The 4.0 OHV engines had non-adjustable lifters. The tapping is from wear on the pushrods / rocker arms. You can buy the replacement sockets for the rocker arms and new pushrods and install them.

 

They are hydraulic lifters, and self adjust, but it is fairly common for 2.9/4.0 OHV engines to have premature lifter failure. If its a knock or a rapping then its the lifters collapsing, but if its "clicking/light tapping" like noise, then its probably valve train wear like it was said.