I got a 2001 jeep cherokee, just replaced the motor with a rebuilt one, 500 miles into using it it starting making a knocking noise, i was told it was the lifters and got them replaced, as well as rocker arms and it continues to make the noise, no pushrods were bent and when the head came off we looked at the pistons and cylinders and there was no visible damge, what else could be the problem

Depends on the noise you are hearing and how the engine is performing with the noise versus before the noise came along. It come be something as simple as an idler pulley making noise which is replaceable in 10mins or crankshaft main bearings knocking which would be more cost/time effective to replace the engine. Need a better description of the noise to diagnose online. Top/bottom, knock/tick, does it go away when idling/under load etc... the more details the better.

Its not the fault with the transmission sensor! its fault with engine heat sensor. try replacing it will solve the problem.

Head gaskets do not make black smoke it is white and smells sweet, is that the case?

DO NOT!!!!!!!!!!!!!!!!!! change oil old oil thick need new lifter

First, if the noise is from the upper part of the engine and is more of a tapping than a knock, likely you have a problem in the valvetrain, most often a bad lifter or worn rocker arm. If the noise is low, deep inside, the noise is from a bearing. This is generally accompanied by lower than normal oil pressure. Regardless of the underlying cause, correcting the cause will not stop the knock. To do that correctly, the engine needs to be removed and all crankshaft bearings and the crankshaft itself need to be replaced (crank can sometimes be "undercut" and thicker bearing shells can be used depending upon the amount of wear.) If caught very early, sometimes only one bearing can be replaced in-car, but in 99% of all cases I have ever seen, most will fail again, sometimes more severely if done this way.

A few questions for you how many miles on the engine? have you had regular oil changes done? This model should have the 4.0 liter engine if so what you are describing sounds like rod knock. The 4.0L engine is designed to take allot of abuse and last for well over 200,000 miles but if regular oil changes are not done you are in for trouble. And the only way to fix rod knock to have the engine rebuilt.

Sounds as If You Have A Chipped Tooth On the "RING GEAR" in the Differential (Rear Alex).
Is this Where You Hear The Noise Coming from? If So Remove Diff Cover With One Wheel OFF The Ground Trans In Neutral Rotate Drive Shaft and Look Closely For ANY Abnormal Surface on EACH Tooth of RING GEAR= the Large one And The "PINION GEAR" the Small one. If you find Chip or Rough spot Diff Must Be Rebuilt. Beyond that A Pinion Bearing can Also Make A Knocking Noise But the "GEARS" Will Be a Rhythmic Noise. I Hope this is of Some Help To You Good Luck !!

these is an old fix, and yes it is ok to do this, but it is better to add a can of Berrymans Chemtool run about 25 miles and drain oil.

These transfer cases do not have plastic pumps. Do have the transfer case looked at by Jeep tech, it could be as simple as an adjustment on the lever.