Hello all I have read alot of post here on this sight aboubt engine knocks but I think I may have a different problem. here goes..
I went ahead and bought the 92 cherokee, 4.0 litre auto,(approx 150,000 miles) I had mentioned that I was going to swap out the engine with a 93 model. When I went to look at and purchase the 92 the lady said it had a ROD KNOCK, I started the XJ it made a slight to moderate clacking or knocking noise but stopped after starting. I drove the XJ home Aprox 15 miles no noise whatsoever on acceleration or deceleration. It does blow smoke when sitting for a minute or two. could this just be a bent or cracked push rod? has anyone encountered this before?
thanks everybody.

"piston slap" maybe? that's common.

If I remember right, a rod knock would change in frequency according to engine RPM's but does not normally go away until repaired, although it may sound likes it comes and goes.