I've heard about them, and I'll definitely believe that the head cracks are what's behind the change to 7 mm injectors in 1991.5, but how common are head cracks?

I've never seen anybody post anything about them on here, nor have I heard about them from anyplace else. How often do they happen, really?

I can imagine that timing advancement, increased fuel injection and high boost pressures all would make crackes more likely?

 

its funny you just posted this I just came into this problem. I think my head cracked or blew the head-gasket. I noticed i didn't have any heat. then i saw air bubbling in the overflow tank. theirs no steam out the exhaust, and the oil shows no signs of water. so its parked for now. i was talking to my diesel teacher at school he says it sounds like a cracked head, and that all of the 12 valves were prone to cracking the head. he said i should put a 24 valve head on it. any ideas before i pull the head?

 

I have seen early large injector bore heads crack before. Common, well on high mileage engines that are worked hard I've seen a few. I don't' think it's all that common when the engine is in a Dodge, unless it's been turned up and run hard.

I certainly wouldn't go so far as to say ALL 12v heads were prone to cracking. The small bore 12v heads are just as good as a 24v IMO. I have seen 24v (and other 4V heads) heads crack in between valves on the combustion chamber side. Heads crack. Nothing you are going to do will prevent all cracks. The better designed 12v head is just fine and I have seen those heads with 800K miles and still serviceable. I think not abusing the head is very important, overheating and very high EGT's will do in any head. Even a big engine like a 3406A CAT!

 

When I had my head machined and o-ringed there wasn't one little crack in it at all. Perfectly straight and clean thats why I decided to stick with the 9mm

 

just got the word on my john deere 300b 38hp no turbo loader tractor. one crack to be welded up. new liners because of cavitation or electrolises .

 

Kind of an interesting thought here; if one of our heads do crack, could they be repaired or would you need a whole new head?

It would suck to pay $800 for head work, then have it crack the first time you pull 45 PSI of boost at 1500 degrees...

 

It's common practice to weld up expensive or rare heads. It depends on where the crack is but most can be welded by skilled welder, or better yet, lock'n'stiched.

 

When my headgasket blew last spring, I took the head to a machine shop for the usual inspection, cleaning, and milling. They found the typical cracks as their manual told them to look for. There were cracks from the intake valve to the injector hole on each cylinder. He went by the procedure in his book to repair each crack and install valve seats to prevent it from reoccurring. I haven't had any problems since. From what he said, this is common practice and I don't have anything to worry about. I think the whole job (mill the head, replace valve seals, clean and check head, complete valve job with replacement of a valve or two, seats, reassembly, etc) was less than $400.

-Steve

 

So, if I were to hypothetically get some custom 9 mm injectors, and then my head cracked, I would be capable of getting it repaired with nothing lost?


If they tend to crack in the same place, would it be possible to get it proactively fixed?

What's lock'n'stiching?

 

Not sure about your first two questions but here is some stuff on the stiching:
http://www.locknstitch.com/
http://www.locknstitch.com/RepairExamples.htm

 

I have actualy seen a cracked head on a B. Not saying thay don't. but I have replaced 4 head gaskets one on mine and for some friends becous they blew ( more like rusted out and leeked to the outside) Look at the pasenger side frount and back and look for spots that look wet or like they have had water leaking down the side of the block. my 96 is doing it to and I know thats all it is just like my 92 did.

 

I took the head from my old 91 to a machine shop, and it had a crack between every injector hole and valve seat. Guy at the machine shop said he'd seen cracks twice that size in Case tractors, and the guys ran them. I did that with mine, and had no problems. I figure 90% of my duty cycle is at <50% load, so I should be ok.

Daniel

 

He's an idiot. You can't just drop a 24 valve head on a 12 valve. Well, OK, you can just drop one on, but it won't work.

Sounds like a blown head gasket to me. You can burn out the fire ring and not get water and oil mixed up.

 

New style cylinder heads for cheap: http://www.tristatecylinderhead.com/...products_id=45. This is where I got mine, but unfortunately I paid the first price listed.

 

The 9mm heads are not as bad as people think they are. Mine as been a good an I run it hard.