EMAXX620

The engine on my 00 is going, very low oil pressure, rod knock and few other small things, but thats pretty much besides the point.

I picked up an 02 4.0 with 79k on it that was pulled due to rod knock (PO swapped an LS1 in his wrangler instead of fixing the 4.0)

i just got the engine up on a stand and dropped the pan, everything for the most part looks okay besides obviously the main bearings and rod bearings. I know i will need to machine the crank, but the PO also has another older 4.0 that didnt have rod knock, and he said i can have the crank out of that if its good.

Question is can i take the crank from one engine (if its good that is) and put it into the engine that has a bad crank and be fine.

2nd, Some of the piston skirts are broken off, but there was no damage to the cylinder walls. If i get pistons, i should be find honing the cylinders and getting new rings im guessing? If you would like pictures, i can go take some. Its just the little tab that sticks off the bottom of the pistons.


Sorry if this is real basic stuff, i have never really done any engine work and thought id ask before i do something considered stupid.

Any help would be appreciated! Thanks

Cherockee

It would be wise for as far apart as you have it you should take it and the parts you want to reuse, to a machine shop that can check the integrity of the parts. You'll also need to replace the cam bearings and maybe the cam itself. You'll want new lifters and I would strongly recommend having the cylinders bored.

Radi

Test fit the bearing caps on the crank and rods with plastigauge. That'll tell you if standard bearings will fit...or if something is excessively worn. A micrometer would be useful as well..both to check tolerance and for out of round conditions.

Yes to the cylinder hone. If there is no damage, a light hone should be sufficient. You need to do this to get the new rings to seal.

Cherockee

Also be careful about those 0331 heads. You should have the one you're going to use checked for cracks. A motor with only 79K miles on it with rod knock and broken piston skirts would really worry me (as it probably did the previouse owner- hence the V8 swap.)

TheJerm

Just because the bearings went bad doesn't mean the crank is bad but will need to be polished by a machine shop and correct bearing purchased. If you were doing it on the cheap then yea you might be able to just swap over the crank and bearings from the non-knocking motor. But thats alot of work for tearing apart 2 motors and not rebuilding them.

And yes hone the cylinder walls to remove any vertical scratch marks and the lip at the top. You will need new rings

edit: and rod knock is relative, I have knock at start up and generally sounds like a diesel. While changing the rear main seal, the main bearings did show pitting, wear marks/scratches and and you could feel with your finger the bearing was not perfectly smooth. But its a 4.0 with 230K milea but I still expect another 100K miles out of the motor