xjfan2979

1.i rebuilt my 4.0 about 5 months ago,with .040 cyl. bore all new cam bearings and freeze plugs.new crank,new pistons,and i reused the factory connecting rods that had 280,000 miles on them.of course rebuilt head and all new valvetrain parts.the problem is when i start the jeep my oil pressure jumps up to about 65 psi and my engine knocks around cyl 5 but i can hear the knock with a stethescope from the crankcase all the way to the valves on cyl 5.i havent pulled the oil pan or anything yet but im trying to get some ideas.the strangest part is the knock is not constant it goes away after about 3 minutes,and the oil pressure drops to about 40 psi at idle.any ideas?

2.when i sort out the engine problem im planning on getting a winch bumper,but im trying to find one that mounts the winch low so it doesnt block airflow to the radiator.suggestions?

Nor-CalJeeper

Stock pistons or aftermarket? Is it possibly piston slap? I'm kind of thinking it is a slight psiton slap since you said it's .40 over and it goes away when the motor warms.

When an engine is cold it is loose, and when it is warm the metal expands and it tightens up the pistons and cylinders.

so my bet is piston slap.

The oil pressure may just be because of cold oil as opposed to it being warmed and thinner.

Does the oil pressure only spike up when the motor is cold or warm also?

xjfan2979

the pistons were speed pros,and as far as the oil pressure it mostly spikes at startup,but does spike when warm sometimes.i would like to avoid taking the whole motor apart to find the problem,but if i have to i will.is there anything i need to look for to identify piston slap such as damage to the piston or head?