1991 4.0L Head gaskets/Heads

[91BiggieGreen]

Little back story on my 4.0L years back I over heated the engine which eventually lead to a very small head gasket leak. Replaced gasket checked head with a straight edge and went on with life, a couple thousand miles later and I REALLY overheated the engine to the point the radiator cap blew off pretty sure the head gasket is shot again. Still starts and runs but not well, well enough to move from stall to stall. I'm digging into pulling the heads over the coming weeks. Replacement heads with valves/springs are gonna run me around 500. Question being do you guys think I should just go ahead and order heads/gaskets/bolts now or should I pull the heads and run them to the local machine shop, check for cracks, resurface and install? Are the heads known for warping/cracking or being problematic. or any other top end things to look out for while im in there? Also is there a limit of how much the machine shop can remove from the heads?

 

[franklin2]

Check with the machine shop and ask what they charge. I have found if you get a local shop to do a bunch of work, the labor is very expensive. You may find you have $500 labor in a set of used original heads by the local shop, or $500 in a set of brand new heads.

 

[91BiggieGreen]

Also going to be doing the glove test just to be sure first followed by a compression check of each cylinder. But judging by the white smoke at startup im fairly certain of the head gaskets.

 

[rumblecloud]

Take a close look at the narrow area between the intake and exhaust valves. They tend develop cracks in that area as well.

 

[91BiggieGreen]

Needing some opinions

Did some prediagnosing on my suspected 4.0l head gasket issue. Just to see what I’m getting into and what to expect

-Did the glove test confirmed inflation and head gasket leak
-pulled each spark plug and found when no.1 plug is pulled glove won’t inflate (also water is coming out when turning over) bingo found the leak
-did compression test on each cylinder first when engine was cold got the following results
6-80psi 5-110 4-110 3-115 2-115 1-60
Then warmed up the engine and the number 6 went up to 105psi

With these results is it safe to say my bottom end is safe? And just pull the heads check for cracks and machine them or replace if cracks are found.

 

[rubydist]

Odds are you will need new heads since the odds of these not being cracked as shown in the photo above are very slim.

 

[91BiggieGreen]

Yea I’m prepared to replace them? Any suggestions of a source? New or remanufactured?

 

[rumblecloud]

When I did my 94 4.0 I picked up new , not reman, from these guys.
King Cylinder Heads. looks like 4.0's are on sale for $299.

 

[91BiggieGreen]

Confirmed cracked head.....also no cross hatches can be seen on the cylinder walls.....thinking a rebuild is in order....really wasn’t looking at pulling the engine but I’m afraid it’s the right thing to do at this point

 

[franklin2]

Confirmed cracked head.....also no cross hatches can be seen on the cylinder walls.....thinking a rebuild is in order....really wasn’t looking at pulling the engine but I’m afraid it’s the right thing to do at this point

Do you have a lip at the top of the bore that catches your fingernail? The rings don't make it all the way to the top of the bore, so you can get a rough idea of the wear in the bore by inspecting the top to see how much ridge there is. There is usually some gook up there also that you need to clean off to help determine how bad it is.

 

[91BiggieGreen]

Will be getting back to the truck monday to clean the block and gasket surface. I'm trying to convince myself that with 110~psi compression check results that ill be safe to rebuild the top end with fresh heads and be safe. Can anyone recommend a supplier for fuel injectors?