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WELP the 4.0 is going to need a head gasket....at least

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Good news: Fired her up for the first time today with a new radiator and water!


Bad news: Water was pumping out of the tailpipe!


Facts: Oil is not milky. Hard to start because its getting wet. Literally tons of steam coming out of tailpipe.


Plan: Tomorrow I will install a new head gasket, valve cover gasket, intake/exhaust gasket, and do a valve lapping and install new stem seals.


Goal: Check the head with a metal straight edge to check for warping. Hope that since oil didn't mix with water that its a gasket leak into a couple cylinders. Its almost impossible to start so I assume its getting into multiple cylinders and making the plugs wet.


Objective: Install new head gasket to see if the previous owner blowing out the radiator (conceivably overheating it) ruined just the head gasket or if the head and/or entire engine is blown. Cranks smoothly but is tough to start so its probably more than 1 cylinder getting wet. Will run and rev fine once started but will blow water out the tailpipe.


Steps Taken: Bought MOPAR head gasket, MOPAR valve cover gasket, MOPAR intake/exhaust gasket, MOPAR valve stem seals, MOPAR thermostat housing gasket, MOPAR throttle body gasket, and NGK copper plugs.


Needs: To know if I have missed anything vital required to reinstall the head with a new gasket to determine extent of damage.

:USAflag: :USAflag: :USAflag:

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Since it sounds like you didn't do compression or leak down tests to determine the head gasket was bad I'm curious if you own a machinist straight edge to check the head. Most heads need to be within .001-.003". You can't use a regular straight edge to check it.



How much water is coming out? 91 should have a conventional cooling system,have you ran it with the radiator cap off ? if its pumping water out the tail pipe you should have old faithful coming out of the radiator

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For sure not trying to cut corners on this AMC icon. I assume the factory gasket is 100% blown and I would assume the has issues. I may have a fresh head later today to bolt on but I'm not sure. Not having white oil gives me motivation but who knows what ill find. If I need to replace a motor I'm not sure whether I'd redo the stocker or get a used one.


So any head gasket replacement tips?

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You might want to pick up some new head bolts as well. Their general age and the excessive heat would be enough justification for me to replace them.


Seems like you have a good idea of what to expect. I would suggest hosing the intake/exhaust manifold bolts with PB for a few days. My guess is that this will cause you the most headache and frustration.

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:agree: 4.0L head is the second easiest head gasket ever (only after the 4cyl rear wheel drive NA volvos)

it should only cost about 200-250 at a machine shop to get the head shaved and valve stem seals and new studs if you break any. so that's one way to be sure if you're worried about it.


for the most part it takes a lot to hurt them though, i doubt its cracked

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Head is fine!!!


Piston is wobbly in cylinder and the previous owner obviously overheated it after the hole in the radiator and then hydrolocked it just driving it and topping it off with water and keeping it running while burning water up. The bottom end is toast.


Need to do a replacement.



Will any 91-99 4.0 long block bolt in with my accessories and 2wd AX-15?

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So my truck is a 1991. According to this page: http://www.jeep4.0performance.4mg.com/tech_specs.html if I get a 92+ 4.0 I need an advanced adapters pilot bearing to use with my 1991 AX-15. Is that correct? Here is the exact quote:


"'89.5-'91 AX15:


OEM pilot bearing 33004041 for '87-'91 4.0 engine or stroker

Advance Adapters pilot bushing 716120 for '92-'06 4.0 engine"


Is that right? There was a change that prevents stock parts from being run?

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