Cracked Head

[jwdvy4]

I had a little too much fun in a mud hole with my comanche and cracked my head. My dad (who thinks he knows everything about vehicles) was afraid that if I put a new head on the block that the lower end of the engine might blow out from the new pressure of the head. I was wondering if it would be more advantageous for me to just find a used motor in to put into it, find a used head, or just get a new head. I am a poor college student and money is very abundant right now. Any suggestions will help in my decision. Thanks for looking.

[Automan2164]

You can try a used head, but I would just find a fresher junkyard motor to swap in. If you are sure you cracked the head, who knows what other subsequent damage occured. Complete engine swaps are pretty easy, and if you can find one for a good deal, you should be good to go.

 

Rob L.

[Geonovast]

*NEW* head, or head from another used motor? A *NEW* head just might do that, but for the price of a brand new head, you could easily pick up a rebuilt or very low mileage motor.

 

I agree with Rob. If you stressed the motor to crack the head, there's probably other damage somewhere. I wouldn't trust that motor unless it was pulled apart, and the block was professionally inspected.

 

You can most likely get a decent used 4.0 for $2-300. That's your best bet.

[Eagle]

Before throwing the baby out with the proverbial bathwater, and recognizing that it's a lot easier to swap a head than it is to swap an engine ... HOW did you crack the head? What's the likelihood of other (collateral) damage?

[jwdvy4]

I was stuck in a mud hole that I shouldn't have been in the first place. My cousin is a mechanic and I had him pressure test it and he said that I definitely blew my head gasket. So I removed the head and had him take a look at it. He said that it was definitely cracked. Most likely I am going to do an engine swap. The only reason I asked about the used head was because I can get one for 100 bucks from one of my dad's buddies.

[jimoshel]

No disrespect meant for your dad or his buddy but neither one of them is right. A polite way of saying they don't know what their talking about.If you were to mill a head down to where you had maybe 14 to 1 compression ratio then you might blow something, like a piston maybe. I can send you a good head, guaranteed for $30 plus shipping. I'm sure one can be found near you for the the same price. Since you already have the head off, run a pressure test on the block. If it's OK, put another head on and go. Jim

[Eagle]

I was stuck in a mud hole that I shouldn't have been in the first place. My cousin is a mechanic and I had him pressure test it and he said that I definitely blew my head gasket. So I removed the head and had him take a look at it. He said that it was definitely cracked. Most likely I am going to do an engine swap. The only reason I asked about the used head was because I can get one for 100 bucks from one of my dad's buddies.

You still have not explained what caused the head to crack ... or what caused the head gasket to blow. Getting stuck in mud typically does not blow gaskets or crack heads.

 

That said ... if you blew a gasket and the resultant overheating cracked the head, unless you got enough coolant into the oil to score the bearings your short block should still be good. Why go through all the work of swapping an entire engine if you can just bolt a head onto it and drive it?

[jwdvy4]

No disrespect meant for your dad or his buddy but neither one of them is right. A polite way of saying they don't know what their talking about.If you were to mill a head down to where you had maybe 14 to 1 compression ratio then you might blow something, like a piston maybe. I can send you a good head, guaranteed for $30 plus shipping. I'm sure one can be found near you for the the same price. Since you already have the head off, run a pressure test on the block. If it's OK, put another head on and go. Jim

 

I do have the means of getting new head for free from another 4.0 that had only 120,000 miles on it when the motor was pulled. It ran fine just the guy was rebuilding the motor for some reason.

 

That said ... if you blew a gasket and the resultant overheating cracked the head, unless you got enough coolant into the oil to score the bearings your short block should still be good. Why go through all the work of swapping an entire engine if you can just bolt a head onto it and drive it?

 

I over revved the engine to the point where it overheated. My transfer case decided that it didn't want to go into 4 wheel drive. That was the cause of the overheating and blown head gasket.

[Eagle]

I over revved the engine to the point where it overheated. My transfer case decided that it didn't want to go into 4 wheel drive. That was the cause of the overheating and blown head gasket.

Nope.

 

Over-revving should not result in overheating. Prolonged idling might, but not over-revving. Unless your fan and/or water pump weren't working.

 

1) Drain the oil, into a clean, OPEN pan. Inspect the oil carefully for evidence of coolant in the oil. If you find a lot of coolant, you may also have damaged some bearings, in which case the new motor might be wiser. If there's no (significant amount of) coolant in the oil, go to:

 

2) Borrow a machinist's steel straightedge and check the top surface of the block for flatness. Also inspect the cylinder bores. If the mating surface of the block is flat and there's no visible scoring in the cylinders, go ahead with the low-miles head. All it'll cost you (apparently) is a head gasket and some time.

[bigd44889]

or you work the motor hard it can over heat

big tires tick mud mud pluging radiator stuck themastat

can all over heat a motor as well

but do what eagle says

i've been there doing head and gaskit this week myself :cheers:

[jwdvy4]

Thanks for all the suggestions. I am just going to put the used head on that I have from another 4.0 and see how that goes.

[Oizarod115]

great decision... if you already have it apart, putting it back together isn't that bad, and a used head should be dirt cheap. slap one on and see what happens, worst comes to worst you buy a used engine and swap it out. :cheers: