Cracked head

Jyrki

Jyrki

Team Member
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Today I got my 320 head back from the shop, where they shaved .178" off the deck. I was really upset to find a crack on the deck, between cylinders, starting from a coolant hole on the spark plug side and leading to another coolant hole on the port side. There wasn't any crack when I took the head to the shop! Or was it there all the time but shaving just revealed it?

I have considerable amount of time and money invested in this head. Is it crap now, or could it be welded up?
 
Where I worked we had a lot of engines welded up over the years. We always had good luck with one company Northwest Motor welders (Portland Oregon). Now I know you live half way around the world so they probably are not an option. But I am sure there are just as good companies in your half of the world. Thy this web site and you will get educated on the different processes that are a used for repairs on heads and blocks. www.aa1car.com/library/ar497c.htm or just Google Northwest Motor welders.
 
Here's a pic of the crack. It's located between cyls number 2 and 3. That's right, between exhaust ports. What's more more, I found starting cracks between the other two exhaust port pairs, too!

I wouldn't be worried about it if it stayed out of the head gasket sealing area. I assume the cracks had already started from the coolant side to the deck side, and shaving the deck allowed them to manifest themselves.

I'll have to look into the proper welding techniques. Some people suggest heating the head to 400 C, welding it, and letting it cool slowly inside rock wool. Others suggest welding it cold using a nickel-based rod, little at a time, hammering the bead immediately while hot
 

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Another starting crack between cylinders 3 & 4.
I would just drill a hole at the end of the starting crack, to stop it.
 

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Did you take .178 of the head for performance, or was there another reason, like significant warpage? I had only heard up to .125 for performance.

The concern I would have is that after welding you would have to surface it again which may remove another .010 or .020.
 
Jyrki said:
Today I got my 320 head back from the shop, where they shaved .178" off the deck. I was really upset to find a crack on the deck, between cylinders, starting from a coolant hole on the spark plug side and leading to another coolant hole on the port side. There wasn't any crack when I took the head to the shop! Or was it there all the time but shaving just revealed it?

I have considerable amount of time and money invested in this head. Is it crap now, or could it be welded up?
Click to expand...
Dover heads can probably repair your head.

Probably, but I live on the other side of the world
 
Last edited by a moderator:
Bob said:
Did you take .178 of the head for performance, or was there another reason, like significant warpage? I had only heard up to .125 for performance.

The concern I would have is that after welding you would have to surface it again which may remove another .010 or .020.
Click to expand...

It was shaved to raise compression to go with flattop pistons and 3.622" overbore. According to Gerry Duttweiler, these heads can be shaved all the way to the spark plug boss or .200". That's what he does on all his engines.
 
Sorry to hear about the head. Hopefully you can fix it. Or should we swap heads :p but still I'd need to fix it, if possible.
 
Twenty years ago we had at least ten shops who could repair a cracked head. Now I was able to find three shops that can weld a cracked cylinder head, or at least try.

1. A semi-retired man who heats the whole head up to 600 C, then gas welds the opened crack, re-heats to 700 C, and lets it cool off in a sealed box for days. This head was too large for his equipment, though. He says not to take the head to the guys welding with nickel rods.
2. A nickel rod welder. This shop has a lot of experience welding cracked exhaust manifolds. They say they're going to weld it cold.
3. A shop using metal spray technology (like when adding material to a crankshaft)

I chose option 2, because I have already invested in bronze K-Liners and brass injector bungs that are pressed into the head. Heating up the head cherry red would ruin all work already done. My machinist also suggested an interesting idea. He would machine a ring, like a short section of a cylinder liner, and press it into a cavity machined into the combustion chamber. It does include some risks, though. The interference fit would seal it radially, but how about axially?
 
There is a method of repair that has been used here for almost 50 years or longer called "stitch welding". Its funny because it doesn't involve welding at all, but is very effective, and was used to fix many Flathead Fords that were always cracking in the valve seat areas. It involves a series of small overlapping holes that are drilled starting at the beginning of the crack, or in your case, as close to the edge of the water port as you can. Then a tapered threaded plug the tapped and inserted into the hole, cut off flush with a hacksaw blade or cutoff wheel, then the next one is drilled tapped and threaded and cut flush, and the process continues slightly over lapping the last plug. Since it doesn't involve heating, welding or stressing the head in any way, it wont compromise any of the work you have already done, and only may require a slight resurface of a few thousandths to cut the cut off plugs stubs flush to the deck. It has even been used very successfully to repair cracked combustion chambers in many OHV engines. Its worth a try before you have the head all warped up from heating and welding and potentially lose all the work, time and money you all ready have invested at this point. Since that is really a pretty low stress area, I would give it a try.
 
I think it's called "pinning" or something like that.
The welder called me today and said he's done, but the injector bungs that my machinist had inserted into the head, leaked when they pressurized the head. They're going to pull them off and put back with a sealer. The injector bung bores were broached, and the brass bungs were precision turned for ample interference fit, but that wasn't enough I guess.
 
I think the process CNC dude referring to is called "Lock n Stitch". It has to be done perfectly or it will leak.


Jyrki: Question on your surface finish. What kind of machine did they mill your head on. Looks odd, like they took several sweeping cuts with a small cutter on a Bridgeport or something
 
Janderson said:
I think the process CNC dude referring to is called "Lock n Stitch". It has to be done perfectly or it will leak.


Jyrki: Question on your surface finish. What kind of machine did they mill your head on. Looks odd, like they took several sweeping cuts with a small cutter on a Bridgeport or something
Click to expand...

Yes, the same machinist who carved my rockers milled the head on a CNC mill. Removing that much material with stones would take forever. The max shave that the automotive machine shops are willing to make on cast iron, is 1 mm. It is supposed to give a final shave on a proper machine once all the porting and valve job is done.
 
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