Old block, new head dilemma

[xjacob903]

I'm sure this has always been a good question for the poor, the knowledge lockers, and in my case... the poor college kid.

Rebuilding the motor is always wantsd, but not all can afford it.

I'd like to hear anyone's stories, experiences, theories, etc. Over installing new/rebuilt heads on a block with, let's say, 150k and up miles on it.

I have a 98 cherokee 4.0 with 249,8xx a day it runs GREAT. But I need a head.. I've done test and I do need a head, but I'm worried about the main rods and or piston rings.

I'd love to rebuild but I can't. I feel like I'm playing Russian roullete.

I have oil pressure and I do not burn oil. I honestly can't make my own decision here

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[MS_Disco]

I'm sure this has always been a good question for the poor, the knowledge lockers, and in my case... the poor college kid.

Rebuilding the motor is always wantsd, but not all can afford it.

I'd like to hear anyone's stories, experiences, theories, etc. Over installing new/rebuilt heads on a block with, let's say, 150k and up miles on it.

I have a 98 cherokee 4.0 with 249,8xx a day it runs GREAT. But I need a head.. I've done test and I do need a head, but I'm worried about the main rods and or piston rings.

I'd love to rebuild but I can't. I feel like I'm playing Russian roullete.

I have oil pressure and I do not burn oil. I honestly can't make my own decision here

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Most of us are in the same boat as you. Want and need is a struggle. I've put plenty of new/rebuilt heads on good blocks and ran for years, granted with the miles you have I would def say start saving up for a complete overhaul. And hey, the head will already be done! Those 4.0s are tough as long as you still have good oil pressure. Just my 2cents. Good luck!

OB#3799

 

[xjacob903]

Even though my bottom end runs great, I hope the new head doesn't blow it to pieces.

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[KYRenegade858]

Maybe check the pull a part yards. Could be that one is close to you. Do a little research and determine what years will interchange as well. You can find them used cheap if you look and maybe with close to the same miles on it. I did this a few years ago with the 3.8 in my 10 wrangler. I had a valve spring break and the head was damaged beyond repair. I was able to find a 3.8 head with close to the same miles and with the egr port I needed at the pull a part yard in Louisville. I think I paid 65 bucks and my time to drive there pull the head and bring it home to install on the 3.8.

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[KYRenegade858]

I didn't rebuild the used one either. I cleaned it up and installed it. At least keep me going. That was at 102,000 miles.

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[Saints&Sailors]

My understanding of the 4.0L heads are that (i) they are relatively easy to remove if you know what you're doing and (ii) if you take the head to a machine shop (not a auto shop, an actual machine shop) they can be relatively cheap to repair. The only way to find out if your piston rings are shot is to pull the head and look.

A hybrid solution would be to buy a head at a junkyard, have that one rebuilt by a machine shop and then, once it is ready, swap the heads. This way you wouldn't be without a vehicle (assuming you can still drive your Jeep as is) and you won't do all the work of R&R the heads for a used part. The risk is that if the pistons are shot, you spent money rebuilding a head and are only half done with the job...

Granted, I've never performed the work outlined above but having a machine shop rebuild/refinish the head has to be thousands less than an engine swap. This type of engine work sounds like it'd be a 4 banana job and I really only have 3 banana skills.

When you say that you need a new head, and you've done a test, I'm assuming you're referring to a compression test and the compression test indicates bad compression in one or more of your cylinders. Out of curiousity, what were the compression values for each of your cylinders? On the 4.0L of your vintage, the valve springs were known to wear out. This could be something as simple as pulling the head, replacing those springs and cleaning up the valves a bit while you're in there. No full rebuild necessary and this could be done in a weekend.

 

[ohiowrangler]

What tests have you done? If the engine is still assembled, I'd recommend doing a cylinder leak down test. This will tell you where the leakage is going, rings/valves/gasket. 150K on a 4.0 isn't a deal breaker, some years had weak heads. I can go into detail on the leak down test if needed. good luck, Ron

 

[xjacob903]

I found that buying a new head is my cheapest solution. I'm pretty skilled, just never done a head.

And yes, I did all of those test and it's a minor blown head gasket, low cyl1 compression, and stuck valves


I actually have 249k on the motor, the 150k was an example

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[theick]

If you have good oil pressure and aren't burning oil than just replace the bad head and keep going. The new head won't cause problems with the bottom end. Deal with everything else latter as needed.

 

[xjacob903]

Got it.

Just waiting for the money to buy everything.



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