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4.0 cracked head

70roadrunner

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ok, im finally going to do the 4.0 swap on my 84 B II. the question i have is regarding a cracked head. it has a crack between the valves, and i need to know if its going into the water jacket. i need the rig in 2 weeks, and i cant find a used head and cant afford new ones yet. im going on a trip for a week, in deep snow and would prefer the B II over my wifes car. i was hoping i could just put it back together with new gaskets and get thru untill summer. thanks for any input
 


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PanamaExpat

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I know this is not so common in the USA but here and in Jamaica there were machine shops that could actually weld cracked heads. How do I know this? The 2H motor in my LandCruiser pick up melted down on a trip home from Montego Bay one afternoon. I thought I was going to need a new head. One of the guys that worked in my bike shop said he knew where it could be fixed. We took the head there and they said ''No problem mahn.'' It had multiple between the valve cracks on four of the six cylinders. It also needed all new exhaust valves. They fixed all the cracks and put in new valve seats and guides. Was certainly a lot cheaper than replacing the head. New or used. Last I heard the old bomber is still running around the island today on that same head.

All you need to do is call a couple of machine shops and see if they can do the same type of work.
 

RonD

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Yes, the common area for a 4.0 head to crack is between the valve seats, and yes, it goes into the water(cooling) jacket.

It takes a special skill to weld cast, but it can be done, new/used head would be preferred, but you go with what you got.

The crack will allow "air" to be pushed into the cooling system each time that cylinder compresses and then fires.
This will displace coolant in the head and make a hot spot until the "air" is burped by flow thru the head.
This compressed "air" also forces coolant in the rad out the overflow because added pressure exceeds the cap rating, so available coolant to cool the engine is less and engine starts to overheat.
So probably not a "driver" unless you want to stop and fill up with coolant all the time.

You can try a head gasket sealer, I used a Rislone product a few years ago on an older truck, sealed up the head leak for about 10 months until I had a chance to redo the heads, it was an older GM V8 used a few times a week to haul things, not a daily driver.
And no it didn't clog up the heater core or rad, lol.
I drained the coolant, flushed system with water, put in fresh coolant and added the Rislone, you run the engine until it heats up then shut it down for a few hours until it cools down.
When I started it back up no white smoke, no bubbling rad, no overheating anymore.
I left it in for about 10 months with no ill effects on the rest of the system, and I did check because I always thought things like this would cause other problems.
It didn't in my case, but can't speak for others.
 

70roadrunner

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thanks guys, i dont have the money to get the head repaired right now. i may try the sealer and see what happens. i will just do my 4.0/m5od swap and deal with the head when i can.
 

CarsonChris

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thanks guys, i dont have the money to get the head repaired right now. i may try the sealer and see what happens. i will just do my 4.0/m5od swap and deal with the head when i can.
Head sealant is a bitch to remove off the deck when you finally do get around to fixing the head.
 

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