The Stovebolt Site Forums The Shop Area Engine Shop The 37 gmc coe had a cracked head ...Not anymore.

Hi, The head was cracked in 4 cyls. and I repaired it and if you want to see how its done and how you can do it, check out the pictures. I hope this helps other bolters that have cracked blocks or heads. Dan

Looks like you drilled and taped the crack, then cut the flush? Was there some welding involved also along with new seats? Looks good no matter how it was done, I really like the flush cut across the whole head, did you do the deck the same way?

Joe

Hi Joe, you find the ends of the cracks and punch them and then drill them one hole at a time and ream the hole with a tapered reamer that matches the tap you will use and then tap it and follow the crack until you plug the complete crack, making sure that you overlap each pin with the other plug, no there is no welding with doing it this way, its called the cold repair, I still have to install seats in this head, I cant do that until I get the guides and then I will install seats and then do the valve job. I like a straight head so I milled the top and yes I did mill the surface side of the head the same way. I milled the top to make the rocker shaft straight when installed. The plugs are made of cast iron so when done right they will expand at the same rate as the head. I will mill the top of the block the same way. then both surfaces will be flat and head gasket will seal nicely.

Very nice, that should be one nice running engine. I have welded heads before, and its a bear to do it right. This is a much better method.

Joe

Benny, from your album it's obvious you know what your doing
when it comes to engine rebuilding.

Although stitching seems to be a fairly common practice when
repairing cracks in large expensive cast iron items I've often
wondered how it can work. The cracks appeared because of uneven
stress distribution in the first place. When you have two
different alloys such as cast iron and the plugs, with two
different thermal expansion coefficient's what happens with the
heating and cooling cycles? I would think that the seam would
open up at some time.
Have you ever wondered about this in your work?

Tks
Denny Graham
Sandwich, IL

Denny, I have repaired many blocks and heads in my time as a machinist, the plugs are made of the same alloy as cast iron, if the repair was done correctly it shouldn't change or leak, I use the bigger plugs because you can tighten them more, the smaller plugs seam to break off too soon for me, yes I have seen a lot of repaired heads and blocks that leak after they have been run and have gotten to hot, but the fact that it cracked the first time means there was over heating or it froze. I would find the reason it cracked the first time, fix that and you should not have a problem. also if this was a 250 or 350 head or block I wouldn't repair them , I would find another head or block that wasn't cracked, because they are cheap and everywhere but being a 1937 GMC 286ci that nobody has, I had to repair the head, it will work great. if its your only choice you have to do what you have to do to make it all better again. Dan

Joe, Thank you! I have welded blocks and heads also and it is a pain, brazing and heliarc welding takes a lot of heat to keep the head or block hot when welding and then bring down the heat slowly and pray that you don't hear that "tink" when you walk away. you know what I am talking about if you have welded heads or blocks. lol.

I figured the plug would have to be a similar alloy or you would
have a problem with expansion.
I had some cast iron that couldn't have been saved by stitching,
so it had to be welded. I've been welding for most of my life
in one form or another. My pop was a maintenance welder at a
Reynolds aluminum plant back when I was a kid in the 50's and he
taught us the basics as soon as we were old enough to hold a
torch. So I do understand the headaches with welding cast iron.
I don't think people realize just how hard a weld is after
welding cast iron. I had a perfectly good manifold on my '50
except for an ear broken off the exhaust flange:
http://www.pbase.com/dennygraham/image/136649244

To just build up the ear was not a good solution because I would
have been tapping into the weld bead so I opted to cut it back
clear of the stud and weld a new piece of material on to the
outlet. That would give me a clean base to tap into:
http://www.pbase.com/dennygraham/image/136649428

Once I had the new tab welded on then I used a drill fixture
that I'd made for drilling flanges:
http://www.pbase.com/dennygraham/image/136650521
I tig welded this using a silicon bronze eutectic rod and it's
held up just fine for the last three years, no "tink" yet.


DG

That's a nice repair Denny! Its a good thing your pop gave you the torch, you learned well! Very cool! I will have to remember this when I run across that problem.. Dan

MY HATS OFF TO YOU GUYS, SIMPLY AWSOME !
Jay D.

I have seen some amazing work on here. This and Denny Grahams' work are some of the best.