It's a SMOKER!

Hey Y'all. I come to you as a new Jeep owner. I recently bought my first Jeep. A 1993 Cherokee Sport to be exact. It just rounded 161,000 today and it has some issues. Someone has to know these 4.0L HO Engines better than I. It smokes at idle, sometimes visible, sometimes not. Does anyone know what are the normal causes of oil smoke in these engines? Is it rings? Valve Guides? Valve Seals? It also has a slight lower end knock at idle that goes away at speed. Oil pressure is 50psi at drive speed, 20 psi at idle. I know it'll be needing a new engine sometime soon but I am trying to make this one last as long as I can as I have a new family to support. Anyone got a core engine laying around they'd like to donate? :-P Any help would be awesome. My personal e-mail is nascarmechanic@msn.com Thanks y'all

These 4.0L get wicked taper in the cylnders and other such wear. See if you can't do a cylnder leakage test. It will tell you alot, also given the milage, ur valve seals have to be close to 'non-existant'. Depending on how ur engine lived it's life, valve guides are a possibility, but i have yet to run into them so severly worn. MY Bet is the rings, but, it could be a combo of ALL!