so i rebuild a 4.0 out of a 99' cherokee and dropped it in my jeep today. got it started and runs great except it vibrates at around 2500-3000 RPM. dunno why. had the crank turned .10 under and put aluminum pistons on and had rods balanced so dunno why in the hell it would vibrate like that . any ideas?

 

did you install new motor mounts? new balancer?

 

new motor mounts and balancer. drove it a lil more last nite. i put a high volume oil pump on it and now my oil pressure bottoms out at higher rpm and the vibration starts. dumped the oil and put in 20-50 to see if i could get the pressure up. works for a lil bit but then bottoms out at high RPM still and vibrates again. the vibration feels like its comin from the bottom end, like back by the flywheel and torque converter or the oil pan. im wondering if its the oil pump vibratin due to lack of oil in the pan...

 

is the flywheel tight?

 

torqued to 95 ft lbs

 

after the vib started i pulled the bottom cover on the tranny housing and checked the flywheel and re-torqued the bolts to the torque converter and changed the oil. thats when i noticed the vib only starts when the oil pressure bottoms out. has anyone else run a high volume oil pump on the 4.0L?

 

id figure out WHY you loosing all your oil pressure........

 

Are you sure the bearings were all the right size. I have got bearing sets before with some that were different sizes. Only found out when the motor would not turn because two rod bearings were too tight. After that I started checking #s and plastiguaging everything. Just a thought.
Thanks Brendan

 

well its not that i dont have pressure, there oil coming out of the push rods fine. jus gauge says it keeps bottoming out and it does the vibe thing.

and the main and rod bearings are all .10 under because i had the crank ground .10 under on the rod and mains. and i know they are all the same because i plastigauged all the mains and rods when i rebuilt it.

 

Keep us posted what you find - I thinking main bearings or oil pump relief valve spring are valves noisy - I have put engines together that had parts in overhaul kits had pump that bad when new - the oil press what would be my main concern.

 

what do you mean oil pressure bottoms out ?

 

the pressure will sit at about 40 then bottoms out. im thinking the oil pump is bad , so i just got a new pump and oil pressure sending unit. gonna put em in and see if that fixes the problem...

 

ya valves are kinda noisy. and mains are new so.... and i put a mopar performance high volume pump in so....im hoping a new pump will solve the prob.

 

sounds like you might want to inspect the rods and mains again...

 

ok so pulled the pump, put in a new one. ****in pump summit sent me was bad , pissed about that one. oil pressure is fine, vibrates jus a lil around 2500 RPM but hopefully once the rings seat it'll go away. also inspected rods and mains, everything looks good. hopefully the ***** will run like a top now.