mike37

but try removing the belt first

diskman

I asked the same question a while ago and I was told by a seasoned 4.0 veteran that the 4.0 is "old-world" design and will not take to replacement bearings unless all the surfaces are machined fresh again. Seems that the original bearings tend to tip and seat a bit off in these motors. Replacing them without machining the bosses would probably be bad.

I would check other things before tearing into the engine. Like someone suggested, pull the belt. Otherwise you might be experiencing piston-slap.

cptcliffhanger

I'll remove the belt first..

"piston slap" never heard of it...

mike37

its caused when the skirt on the piston looses it flare

cptcliffhanger

quick google on piston slap tells me not to worry about cause there's Nothing can be done short of a complete rebuild.

Not to mention piston slap really wouldn't care about oil pressure like the noise I'm hearing.. tends to mostly go away when after a few seconds.

mike37

any new info

GrantMLS

cracked flex plate? Always sounds like a rod knock and goes away when it warms up.

cptcliffhanger

well I took the oil pan off yesterday (not so easy) the rod bearings are def scored, and unfortunatly modified the journals' surface too....

I'm guessing I need to get a new engine or rebuild this one.. oh well..

jeepfreak82

Just as a thought, my buddy has the same problem in his '92 and we came onto the conclusion to run lucas oil stabilizer with the oil changes to get him by until he can overhaul or swap out. It really seems to help in his... Just a suggestion

cptcliffhanger

well I already got the bottom end open.. I may as well try to put in some new bearings and see what happens..

any suggestions on bearing size? stock, .010 over. the crank hasn't been ground, (i don't think) but it has worn (160,000 miles)

mike37

you need to go with what ever was in it pop the bearing out it will say on the back .010or whatever if it doesn't its stock

personally if its scored leave it you run the chance of spinning the new bearing on a scored journal

cptcliffhanger

scored is a strong word..

it's more burnished.. if you run your finger around (circumference) the journal, it is smooth.

if you run your finger across it, it is lumpy.. but not really scored.

cptcliffhanger

also.

where can I get the bearings?

if I use a plstigauge, what clearence is the correct amount? maybe I can pick my bearings that way..

mike37

any parts store will have them or can order them
you should replace with the same size that came out
I think you can get off size to adjust for the wear but you really need to know your stuff to do that

I dont know the clerance for the 4.0 but your parts store should be able to tell you that also

cptcliffhanger

well if the plastiauge tells me there is .020" of clearence, I prolly need +.010" bearings..

S