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Cracked Head...other damage??

4

4jeep4

NAXJA Forum User
Location
California
Hello all,

I just bought a 2000 XJ 4.0 with a cracked head. (Didn't know it when I bought it). Anyway I went ahead and ordered a new head from Clearwater. My question is, is there away to see if the bearing are toast before I bolt a new head on, or anything else for that matter? Is it worth taking to a mechanic?

From searching on the forum I have tested the oil pressure with a manual gauge and have great pressure at cold/warm temps and idle/high rpm's. (Between 25-70) The motor sounds good to me and ran great while I drove it home.

The motor has 81,000 miles and was a Government Park Ranger vehicle before me. Any suggestions would be appreciated. I already washed the jeeps with my tears when I realized the head was cracked I don't want to wash it again if the whole motor is going south.

THANKS!
 
The bearings are probably fine. The only way to check would be to pull the oil pan and pull all the bearing caps. Which if you are doing that might as well replace them with the caps pulled.
 
Alexia said:
The bearings are probably fine. The only way to check would be to pull the oil pan and pull all the bearing caps. Which if you are doing that might as well replace them with the caps pulled.
Click to expand...

Cool thanks for the reply. I really hope they are ok. I'm a novice when it comes to tearing into a motor. Is replacing the bearings a very difficult job to do in your garage?

With the Jeep being down and out while I am doing the head I would like to do anything else I can, while I'm in there. Should I consider replacing the bearings as well?

Thanks for the help.
 
Oh wow man, that's weird. I'm in the exact same scenario, I just haven't ordered the new head yet. Although I knew about the cracked head when I bought it.

You can also get the oil tested by Blackstone Labs. They can test for high levels of metals from fried bearings.

I'm interested in finding out if a compression test will yield usable results. I assume that cylinder 3/4 will read low regardless based on the crack, but will 1,2,5,6 be helpful?
 
4jeep4 said:
.......
From searching on the forum I have tested the oil pressure with a manual gauge and have great pressure at cold/warm temps and idle/high rpm's. (Between 25-70) The motor sounds good to me and ran great while I drove it home.

The motor has 81,000 miles .......
Click to expand...
I think the bottom end's OK. If the oil looks good with
no visible evidence of coolant (milkshake appearance),
there probably wasn't enough coolant mixed in to
cause a problem.

BTW, just out of curiousity, how much do these 4.0
heads weigh?
 
4jeep4 said:
Cool thanks for the reply. I really hope they are ok. I'm a novice when it comes to tearing into a motor. Is replacing the bearings a very difficult job to do in your garage?

With the Jeep being down and out while I am doing the head I would like to do anything else I can, while I'm in there. Should I consider replacing the bearings as well?

Thanks for the help.
Click to expand...

Depends, do you enjoy holding 55 pounds above your head with one arm while attempting to not only get the journal bearings on also bolt the caps into place? The journals would also have to be measured to order the correct replacement bearings.

Basically, unless you know there is damage, leave it alone.

Runnin'OnEmpty said:
BTW, just out of curiousity, how much do these 4.0
heads weigh?
Click to expand...

Around 75 pounds with the valves, rockers, and springs.

A 4.0L weighs around 500 pounds with some bits bolted on.
 
Last edited:
The oil definitely had some milkshake to it, but hope it wasn't in there long enough to cause much damage.

Thanks for the help. I will put my new head on next week and hope for the best! :)
 
ditto, just do the head and hope for the best. At this point that's all you can do..

I guess the good thing is that if you need to you can replace the bearings with the engine in place.
 
The rod bearings would be the first to suffer from a cracked head. If you are worried, pull the pan and have a look. Replace the RMS while you have the pan pulled. Realistically, if you pull the pan and find the rod bearings are shot, you would be pulling the motor to have the crank ground... So, I'd leave it alone if pressure is good and there are no lower end knocks.
 
Tony_SS said:
ditto, just do the head and hope for the best. At this point that's all you can do..

I guess the good thing is that if you need to you can replace the bearings with the engine in place.
Click to expand...

Chances are, if you need bearings the crank will be scored. Rolling in new bearings on a scored crank will trash the new bearings quick.
 
Thanks for all the info. When replacing the head should I be replacing pushrods/rocker arms/lifters as well. Or is it an ok practice to reuse them?
 
4jeep4 said:
Thanks for all the info. When replacing the head should I be replacing pushrods/rocker arms/lifters as well. Or is it an ok practice to reuse them?
Click to expand...

It is fine to reuse them, but inspecting them for excessive wear is a good idea. Just make sure to put them back in the same spots/order you removed them from.
 
Alexia said:
Depends, do you enjoy holding 55 pounds above your head with one arm while attempting to not only get the journal bearings on also bolt the caps into place? The journals would also have to be measured to order the correct replacement bearings.
Click to expand...
The crank shaft won't fall out even if you remove all the caps. The torque converter and timing chain will hold it in. As for the journal size, its usually on the back of the bearing what size it is. Even if the journals were worn enough the crank needs to come out and be turned. You can't put undersized bearings in w/o having the crank turned. That would be .010" wear, which would be massive.

The crank also doesn't have to be dropped very far, if any to change the main bearings. Its a pain though. The top ones can be rotated out by putting a aluminum cotter pin in the journal's oil hole and rotating the crank shaft. The cotter pin will push the bearing out while deforming when it gets to the block.


If the oil pressure is good and no knocking sounds i would replace the head and run it. Do a few oil changes to get the coolant out. One around 200 than one around 500.
 
4jeep4 said:
Thanks for all the info. When replacing the head should I be replacing pushrods/rocker arms/lifters as well. Or is it an ok practice to reuse them?
Click to expand...

As said, you can reuse them if they look good. Also, if you pull the lifters make sure they go back in the same hole they came out of. I would do one by one so as not to get them mixed up.
 
I'd clean each lifter (after removing) with penetrating oil, then make sure it pumps up good with oil. Seems like most XJ's have noisy lifters. Make sure they get back into the same hole.
 
Thanks for all the advice guys, I appreciate it. I inspected everything and it all looks good, I'm all ready for my new head. Now its just the waiting game, now I wish I paid for expedited shipping. :)
 
Another question, when installing the new head has anyone had success with attaching the intake/exhaust manifolds to the head while its out of the the jeep and lowering it in, all at the same time?
 
You could do that but its a PITA to bolt the upper flange up to the exh manifold. At least on a 2000.

It's actually not hard to get to lower bolts...just use a crate to stand on so you can bend over in the engine bay.
 
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