Cracked 'B' head.

jjk

jjk

Member
Got a killer deal on a 31 high compression head recently and discovered some cracks during clean up. Before I spend a bunch of time and energy on it I decided to seek some advice from the elder statesmen on what could be done.

I circled the cracks in the photos and just curious how far I will need to go to run this safely.
 

Attachments

  • ke6d62g2.jpg
    ke6d62g2.jpg
    20.3 KB · Views: 215
  • RenderedImage.jpg
    RenderedImage.jpg
    46.7 KB · Views: 235
If the crack runs from a water passage hole to a stud hole, a simple repair can be made. Cracks between water jacket holes do not create a problem. I have had them repaired by having an automotive machine shop drill out the stud hole and install an appropriate size valve guide in a press fit manner. The valve guide is then drilled out to accommodate the head stud and surfaced with the head. It worked for me.

John
 
I have a Brumfield Head and talking with the late Larry B. It had the same crack as you show he said No problem in running with the proper copper gasket and copper spray!
 
I have used a couple like that.The machine shop that shaved them for me said Ford has a part number for those cracks.I have one that I had planed about 10 years ago,greased up and sitting in the shed waiting for me to use it.Same cracks in that one.
 
I don't think I have seen an original Model A head that doesn't have those cracks. My advice? ignore them and drive away.
 
40 years ago i drilled and tapped the same crack for a small machine screw, cut it off a little above flush and peined it with a hammer, leveling with a file
 
I brazed up my stock cyl. head and had it surfaced no problems .the surfacing had to be done with a belt type surfacing machine due to embrittlement after the brazing .
 
Thank you all for the advice im going to give this one a chance at a new life and run her with my fingers crossed. I wanted to make sure I wasn't setting myself up for failure after all my work was done.
 
Even though not mentioned here make sure to use proper torking sequence when installing
This cracking can be caused by not following the proper procedure

J
 
For sure I'm doing new studs so there will be a few passes with the torque wrench during install.
 
Cracks initiate in a tension stress field in the metal. In this case, tightening the head stud put a bending stress on the head so there was tension in its bottom surface. Contributing to the crack initiation is the rough surface finish on the walls of the coolant holes. I put arrows to show the tension fields in the metal from bending the head due to nut torque and a gasket that compresses.
In my opinion, the stud is going to weep coolant because of the cracks that will open a bit when the head is torqued. I would have a shop oversize the stud hole and press-fit a bushing into the stud hole. I would also grind the water passage holes smooth using a rotatary tool like a Dremel.
 

Attachments

  • Cracked B Head.jpg
    Cracked B Head.jpg
    44.6 KB · Views: 78
Bob Bidonde said:
Cracks initiate in a tension stress field in the metal. In this case, tightening the head stud put a bending stress on the head so there was tension in its bottom surface. Contributing to the crack initiation is the rough surface finish on the walls of the coolant holes. I put arrows to show the tension fields in the metal from bending the head due to nut torque and a gasket that compresses.
In my opinion, the stud is going to weep coolant because of the cracks that will open a bit when the head is torqued. I would have a shop oversize the stud hole and press-fit a bushing into the stud hole. I would also grind the water passage holes smooth using a rotatary tool like a Dremel.
Click to expand...

Bob, Pls correct me if I'm wrong but tightening the head studs in the recommended sequence (starting in the middle and working towards the ends) would create those tension forces at the bottom face. I have seen people recommend starting at one end (either end) and working towards the other. I can't see that making much difference though.
My thinking is that many small increases in the torque setting is the best way of minimising stresses in the bottom surface.
Comments?
 
Synchro909,
Here is a diagram of one nut clamping down on the cylinder head which sits on a compressible gasket. When the head bends under the influence of tightening the nut, the top surface of the head goes into compression and the bottom goes into tension. You are correct. At each tight nut, there will be a local tension stress in the bottom surface of the head. That is why we see cracks in the bottom of the head and not the top.
 

Attachments

  • Bent Head.jpg
    Bent Head.jpg
    19.3 KB · Views: 10
Thanks for the info yall, I'm looking for a local machine shop to sleeve the stud hole and do a quick pass on the surface for me.
 
I have had good luck with the Best brand graphite gasket with the copper spray gasket adhesive. Best makes their graphite gaskets for stock and for high compression heads.

Terry Burtz recommends not using the traditional head nut tightening sequence but starting from the ends and only using 10 foot-pound increments of torque. So 10 ft-lbs, then 20, then 30, then 40, then 50, then 55.
 
nkaminar said:
Terry Burtz recommends not using the traditional head nut tightening sequence but starting from the ends and only using 10 foot-pound increments of torque. So 10 ft-lbs, then 20, then 30, then 40, then 50, then 55.
Click to expand...

I would not recommend this procedure.

I would torque in the normal pattern but initially snug each stud and then tighten to 35 ft-lbs and increase 5 ft-lb increments up to 55 ft-lbs.

This is what I do,

Chris W.
 
CWPASADENA said:
I would not recommend this procedure.

I would torque in the normal pattern but initially snug each stud and then tighten to 35 ft-lbs and increase 5 ft-lb increments up to 55 ft-lbs.

This is what I do,

Chris W.
Click to expand...

Yes but the OP's head has cracks around stud #2 in the "spiral" pattern, so if you use that pattern, that part of the head will have consistently higher strain on it than the parts around it. So a modified pattern might be indicated in this case.

I can definitely see the argument for Terry's back-to-front pattern. The underlying question is whether you think the cylinder head, with its 2x7 bolt pattern, is more similar to a one-dimensional linear bolted joint or a two-dimensional rectangular joint. Two-dimensional joints should be tightened in a spiral outward from the center, while one-dimensional linear joints should be tightened from one end to the other.
 
You must log in or register to reply here.
Back
Top