Uneven Head Dome Sizes

Cameron Koehn

Cameron Koehn

Member
So...I had someone shave my EAB heads just for a better sealing surface. They came back with that circle of dome progressively smaller towards the back of the head. I'll get a picture tomorrow. Is this something to be concerned about?
 
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It sounds like they milled it at an angle.
Not good.
If the smallest still gives enough clearance, it could be re-milled to equal them up.
It might be a casting flaw, and the milling has made it more clear.
You need to take careful measurements to work out what happened.
The odd sized domes will lead to inconsistent compression ratio and the difference in squish may effect the smoothness of the engine.
Mart.
 
Whomever did the work, didn't know how to setup these heads in their machine . . . or didn't know how to use the machine, or both. Post some pics so we can get the jest of how far off it is. Depending on the heads and application (piston height), you may not be able to mill them more. Hopefully the dome cut-outs are not already too small and the heads too thin.

I've seen a ton of older aluminum heads that have had the Hell milled out of them. The first issue is that the deck surfaces become too thin (making sealing an issue). The second issue is that the heads may need to be re-domed (not a cheap operation).

Pics will give us something to ponder . . .
 
And, as insurance, start looking for a replacement head. I had to have a head angle milled (front to back) to match a incorrectly decked block. I took .039" more off of one end, and the while the "circle of the dome" was progressively smaller, it was not that noticeable. It sounds like yours could be off even more than that.
 
It is likely the head was "warped" when the machinist tried to set it up. Most used iron heads are low in the center when fixtured under the mill cutter or grinding wheel. Some much worse than others. I straightened those with serious warpage before milling in order to retain reasonably equal chamber sizes. The end chambers can become considerably smaller, if not starting with a flat gasket face, by the time cleanup is achieved.
 
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You might consider using a depth mic on the valve pockets and see if the settings are close .
There is a possibility that the original chambers were mis machined above the piston .
After all,,,,,even back then,,,,,all things were not perfect when new .
Machine settings could have been off,,,,or someone was having a bad day,,,,,or even training a new guy .
Check it and see for sure .

Tommy
 
A complete mess . . . they're really not usable at this point. I'd be looking for another set of heads and a different machine shop. They've been way over-milled on one end - there is no way to "bring the material back".
 
Ouch! Just asked for a cleaned up surface and that's what you got??? Wow...somebody needs a kick in the butt. Those heads are door stops now.
A little time spent setting up the cut would have prevented this...what a shame.
 
CK>>>I had someone shave my EAB heads just for a better sealing surface>>>


Do you perhaps have a 'before' pix?
 
If it were mine, I'd prolly tell the shop to tilt the machine the other way and shave the heads again FOR FREE so all the domes match like they're supposed. And smooth out the dome edges FOR FREE too while they're at it! Then figger out how to provide enough headroom to avoid piston & valve contact.Think of the compression this might make from this mistake! 8^)
 
Well after some more extensive measuring, the head was warped and the machinist took all the warpage off one side. To make myself feel better, I'm telling myself that it was warped beyond repair to start with. Maybe that's not true. And, yes, I will be using someone else in the future. Vintage Hot Rods from Chico, CA, I will try them.

I almost cried when I tried to find the "before" pictures of the heads and realized that somehow I never took any. Took lots of pictures, but none of this.

Okay! I'm on the lookout for some good stock EAB heads. I do have a set of 8BA heads, but they are corroded pretty badly and i think they are slightly less compression, correct?
 
CK>>>the machinist took all the warpage off one side. To make myself feel better, I'm telling myself>>>


You're obviosuly a nice guy CK. I'm prolly not as nice as you. But if it were mine, I'd still tell my machinist to try to make all the domes the same size and edges smooth FOR FREE to make myself feel better.


As for corroded or pitted heads, I've used JBWeld to fill the pits if heads aren't warped. Smooth the cured epoxy with ScotchBrite pads. Seals fine with well-greased head gaskets. The other option is to give your machinist another chance on a light shave job to make the pits small and shallow enough to be inconsequential---FOR FREE again.
 
When you go to Vintage Hotrod in Chico . . . make sure you say "Hi!" to my good friend John Beck (he's the one who will probably do the work on your heads).

He has helped us dyno tune the FlatCAD Bonneville engine (at his facilities) - really knows his stuff and is a heck of a solid dude.
 
They may have been milled before too. I always look at the bottom of the thermostat housing area when judging used 8BA family heads. If there is a good step between the bottom surface of the stat housing area and the head deck parting surface then the heads may still be a standard dimension. When you see one that is flush or even milled like those then you know it went too far. The dome areas and valve recess areas can be opened a little bit with machine work but that just makes the casting thinner there and can lead to heat cracking.
 
Good for you noticing that they ruined your heads before you installed them and created even more problems. Never go back to that machine shop unless you think they will buy you another pair of heads.
 
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