I just picked up a 97 4.0 with 158k on it (to replace my 94 4.0 with 242k). It's got a brand new crank installed (not sure why it was needed), new timing set, and new oil pump. I pulled the head today as I'm going to get it cleaned, milled, valve job, etc.

I'm wondering what else I should do it to it while it's apart. At 158k I wouldn't expect piston rings to be bad, but I'd also feel better knowing they've been replaced. My current engine is suffering from blow-by that's sending oil out of the dipstick tube.

Should I be looking into replacing pushrods, lifters, springs? On one hand, tearing it down entirely and having the block hot tanked and gasket surfaces milled flat would seem like a good idea. On the other hand, that all adds up and I'm not sure it's necessary.

Any advice?

 

Why does it need tearing apart or is it torn down already

 

It doesn't need it, but I'm not going to put a 160k motor in and trust it without refreshing it.

 

Have you performed a compression test? Does it run?

 

Without the numbers from that engine you have little to go on as to what needs to be done to it before it goes in your XJ.

 

give the head a good port and polish while your in there, and some ls1 valves if you want to get crazy throw a mopar performance head gasket on there to

in all seriousness tho, i'd pull it apart and look everything over, you dont want to swap it in with a fresh head and you throw a rod, or blow a piston skirt to peices

 

The machine shop can test the springs when they do the valve job.

Make sure they change the valve seals.

Change the lifters if you'd like as the head must come off to do that.

The bottom ends on 4.0's can last a very long time with nothing more than oil changes at regular intervals. They will break from time to time, or suffer and wear out prematurely if the previous owners neglected routine fluid changes. I would be more concerned about why the changed all those other parts and if that work was done properly. Maybe the oil pump broke and ruined the bearings.