Milling a B head

Art Bjornestad

Art Bjornestad

Senior Member
If a stock B head is about 5 to 1 compression, could I take about .125 off of it instead of buying a new head? If anyone has tried this, were there any problems. Seems like that was the only way to cheaply bump the power in the old days.
 
Art,
A stock Model "B" head has a 4.6:1 compression ratio. I milled a Model "B" head so that there was 0.01 piston recess remaining. Compression gage pressure was 93 psig. Carbon knock became a problem because there was inadequate clearance to the piston top.
The Model "B" water pump is not as good as the Model "A" pump because they have thin, and in many cases a porous casting. I would use Snyder's 5.5:1 Model "A" head, and a Model "A" water pump with the modern roller bearing up front, and a double seal in the rear.
 
i also use the 5.5 head , but with .050 milled off . now its 6-1 . i also use the leakless water pump ! ............ steve
 
BTW the head "with the large 'B'. uses the standard Model A 4 hole water pump and is 5.22 to start with (vs 4.6 for the "head with the large 'C' ") . The "Large B" head worked fine for me from 1962 till last year (40,000 miles) when I got a 7.0 Lion head.

For the record I would not mill a head .125. That would eliminate the round "flycut" cutout above the pistons and allow no clearance space if the pistons come up above the deck.

With any higher compression head you MUST use less spark advance and retard the spark on hills and long pulls. As I remember Rich owner of the "Sokie, IL engine rebuilders" recommended a max of 28 degrees with a 6.0 head.

Twenty-eight degrees is alittle less than 3/4 of the distance from the retard position on the spark quadrant. Max on the quadrant is 40 degrees.
 
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This is a A head...
P8200011.jpg
 
I recently purchased a BB motor and trans, the head has F3 on it, anyone know what F3 means?
 
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