Replacing Cylinder Head - what to look for..

I'll be replacing the Cylinder Head on my 90 4.0L this weekend, and was wondering if anyone has any suggestions as to what to look for whilst the head is off - I'm considering also replacing the rings, big ends and the oil pump at the same time -the engine has done over 200k miles and the oil pressure is somewhat low - 10~15 psi at hot idle, there is a definite knock from the bottom (louder when cold and especially when the engine first starts) and the compressions are on the low side but OK.

Any suggestions as to whether this is a good idea or not would be appreciated - I've searched and seen all sorts of opinions, and I'm in two minds myself as to what to do - I could replace the rings with the engine in the car, but would this improve compression necessarily - the old rings should be nicely bedded in by now ;-) - same thing applies to the big ends - replacing the bearings *may* actually be a bad move, given that the current bearings will be the same general shape as the crank, just bigger....

So ... replace rings, big ends and oil pump at the same time as the head, or just throw the new head on and step away? Anything in particular I can look for whilst the head is off to help make my mind up one way or the other?

Thanks everyone....
Graham

if i was going to do all that i'd just pull the motor and do a complete rebuild

XgeekstarX said:

if i was going to do all that i'd just pull the motor and do a complete rebuild

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Second on that, unless your looking for the exercise of crawling under and back out a few dozen times...pull the motor and put it on a stand..

Ditto, leave it alone. You can swap this head back onto a new motor when it's time. If you've got to ream a ridge to get the slugs out.....

(IMO) At 200k new ring would be a near waste of time. The bore is so out of round that new rings will never seat right. If even as well as the old ones. Piston to bore gap is huge and the ring grove has grown WAY out of spec.
If the rest of the Jeep is clean do a full reman of the putter. Else pop on a used head maybe a new pump and drive her till she drops. LUCK

Thanks guys - I'll stick on the new head and call it good.

Why are you replacing the head?

grahamtwatson said:

Thanks guys - I'll stick on the new head and call it good.

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It sounds like you've got a problem with a main or rod bearing, not the head. I'd forget doing the head and swap in a whole engine. The 4.0 I6's are pretty cheap, call some junkyards and ask around.

Oh the symptoms described are *additional* things that I was thinking of taking care of at the same time - I'd managed to snap off the rear exhaust stud inside the head, and from everything I'd read on this board, the head had to come off to fix that, and given the high milage, poor fuel consumption, somewhat low vacuum pressure and compressions, I decided if I was going to take the head off I may as well replace it with a reconditioned one. So the thought was ...