HockeyFan56

Brief history, bought this Jeep ('97 cherokee) from my nephew after much abuse. Head was cracked from repeatedly overheating it. Bought a $200 craigslist motor and started playing with the mods. 30k miles pass. About a year ago it developed an odd rattle/knock. Kinda sounded like a rod but wasn't constant. Shopped around and found the $200 motors don't exist any more so I decided to rebuild it. In the process of pulling it I find a torque converter bolt backed out and hitting the plate between the motor and tranny. Here's my noise but I'm down to motor mounts and transmission bolts before it falls out. Skip it I'll rebuild it anyway. I set a $1000 budget.

It came apart fine and looked good. Crank had a few waves in it but it measured within spec. I found the only local machine shop and took them the block and crank to see if they could polish the crank and dip the block. I had already miked the block and crank and while the crank was close the cylinders were within factory specs. I felt a hone was all they needed. The machinist disagreed. With nothing more than a visual inspection he rattled off $1800 of machine work I "had" to do. I can get a 4.7 for less that $3k so that doesn't make sense. Finally I just told him turn the crank, dip the block and install cam bearings and freeze plugs. Half my budget gone.

Things come back and look good and I'll admit I didn't check clearances just cleaned everything up and threw it together. New bearings, rings, oil pump, and timing set. Started up fine and sounded good, early on after one of my first test drives I was sitting in it idling and the oil pressure gauge goes from 40 to 80 to 0 back to 40 in 2 sec. Well that was weird but the sound and lope of idle never changed so no worries. I drive it the 35 miles to work and along the way I notice the oil pressure dropping on the interstate until it hit about 10 psi at 70 mph. I pulled off and shut it down. Cooled it down and finished the trip. Added a qt of lucas and drove it home, had to stop twice to let it cool to help the oil pressure. Swapped to a high volume oil pump, no help. Total 100 miles. Mechanical gauge added and verified gauge is close enough to spell trouble.

Pulled the motor back out to find exactly what I expected, every bearing in it is beat. I buy a crank kit and cam bearings and this time check clearances, all good. Cam seems a little tight (can't spin it by hand) but I can't plastiguage that one so I move on. I also replace the lifters because 2 of the rockers weren't full of oil when I pulled it apart.

After 60 miles when it gets hot the oil pressure has been steadily dropping. I'm down to 20 psi when the oil is hot. I've read they need 13 psi at idle so I have that but am I doing damage anyway?

At this point I'm looking for a SBC adapter plate but have a hard time admitting defeat. Did I miss something? I've build SBC and motorcycle motors and have never had this much trouble.

I'm open to suggestions before I pull this thing out again but I also don't want to burn every bearing up so I can't tell where the problem starts again.

Lmao_37

Sorry bud I don't have a clue what's wrong but good luck in finding the problem.

s346k

so you never plastigaged any of the bearings upon assembly? I'm assuming you reused the old cam and lifters..? were the bearings sized properly after having the crank cut?

97grand4.0

distributor not seated?

Radi

I don't have any suggestions that don't involve opening the motor up again.
20# is just fine at idle, but a brand-new rebuild should do better and the fact it's been dropping rapidly doesn't bode well.

The problem is starting in the same place: improperly fit bearings. First time the crank bearings weren't checked, second time it was the cam.
At this point you're looking at disassembling it again to see where the problem lies.

md21722

20 at hot idle

40-50 going down the road at 2400rpm for 20 or more miles

are good ball parks

If you are only getting 20 going down the road your engine is unlikely to last long

Fred/N0AZZ

Think you would be money ahead having someone else rebuild it, skimping on machine work can bite you in the long run.

Bocefus

If you don't want to spend the money for a professional full rebuild or a reman, your only real option is to find a good used engine. They are out there. Check http://www.car-part.com/

97grand4.0

20 lbs at idle is miserable. What is the cold idle pressure? Was leaning toward a spun cam bearing the first time around. Cam wont turn by hand, that don't sound so good either, sounds like assembly went wrong, maybe pushed a bearing? Leaking by an unseated cam bearing would drop the pressure quickly. .and sure dry up that bearing and the corresponding journal. Installing a cam is tricky business, oil holes to line up, adjusting the tool so not to deform the bearing while just enough to drive it in, working from back to front..and cam bearings can be a bear with the block in the vehicle...if not impossible.

HockeyFan56

No, I didn't plastigage anything the first time through. Second time in I checked the rods and mains and everything was within factory spec, .002-.0015 or so. Reused the cam and lifters the first time also but went to new lifters on the second try. I'll pull it again soon, my need to know out weighs common sense at this point.

HockeyFan56

On another note once i have it out I can measure it for a SBC adapter plate.

Cold pressures are 40-60 range. Cold/hot being the oil temp not the water temp.

97grand4.0

Mine is 40 only drops a little at hot idle. This is a good one. Your main and rod clearances, if accurate, are spot on.
Engine pressure really is acting like excessive clearances, good cold drop hot. You say you changed the oil pump? How are the rockers oiling up do they look like a ton of oil or a bit starved? Could it be a problem with the gauges ..?

HockeyFan56

Added a mechanical gauge early on so I'm trusting the numbers. New high volume pump is in there too. I think excessive clearances are going to be the culprit again but I'd like to find out whats eating the bearings so fast.

97grand4.0

Did you have the crank turned? Or at least polished? How about resized, with oversized bearings? Surely if not it would eat bearings.

I remember once I had a buick V6 that the journals on the crank (rod journals) were so rough, it would have turned down to even lower than oversized bearings would accommodate. So, I opted for a 'rebuilt' crank, what that consisted of was ,they weld up the journals then cut them down, and you go with oversize bearings.
Big mistake. After about 10k I was getting off the highway cloverleaf one day, and there was a KLINK! .. dead, with all red lights on the dash. The crank had snapped in half. I took it to a metallurgist engineer, a PE, who analyzed it. Results....when the crank is worn that bad, it cant handle the torque, regardless if it is welded up.
All the torque is transmitted along the original casting (and deep groove fault lines) , not the welded material comprising the new bearing surface. Welding a crank is lipstick on a pig.

HockeyFan56

The first time I had it turned the second time I bought a remanufactured crank.