Milling the head

1

1930deluxe

Senior Member
How many thousandth can be removed from the head without a problem? Will milling the head cause a problem with the distributor shaft?
 
Not much! Stock pistons protrude above the block some, more if the block has been surfaced. You need a minimum of .030" of clearance between the piston and the head because the rods stretch when running, more so at high RPM.
 
Jim Brierley said:
Not much! Stock pistons protrude above the block some, more if the block has been surfaced. You need a minimum of .030" of clearance between the piston and the head because the rods stretch when running, more so at high RPM.
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Jim
.030 with or without a gasket?
Terry
 
I have always heard that .125 (1/8") was about the maximum that that could be taken off. That being said, the stock A head is a 4.2 Comp. Ratio, a B head is, I believe 4.6. Someone, somewhere can tell you what 1/8 off the head will give you for a Comp Ratio. I took .040 off a stock A head with good results, but not spectacular results. The problem with a stock A head is the Combustion Chamber is so deep that taking even .125 off doesn't change the depth very much. The problem with a B head is that you must have a B water pump (3 bolt) to go with it. And the B heads are prone towards cracking just about dead center. The crack doesn't seem to mean much, but no one likes having cracked parts in their cars. The best answer is a High compression head from Snyder's at 5.5 or 6.0 C.R.
Terry
 
Gunmetal blue2 said:
You can also cut some of the top of the pistons off. In regards to Jim B. statment
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I've just been through this issue while having the bottom of my motor rebuilt. My block had previously been bored out to the max (0.125") and decked quite severely. It had compression of 80 +/- 2 psi all round. The rebuilder said that the pistons were coming out of the block at the top of their stroke and fouling the (standard bore) head gasket. His solution was to take a chamfer off the top edge of the pistons.

Haven't re-installed it in the car yet.
 
I had to have my distributor shaft shortened to accomodate a milled head of unknown provenance. Luckily I had a friend with a programmable milling machine. But, I used it with no problems for several years.
 
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Hoogah brings up a good point. My previous engine was decked .030 and the head was milled .030. when I swapped the head to my current engine it was standard deck. The decked block was unmarked. You'll definitely want to clay ball the clearances at the very least. I've seen friends double up on head gaskets after milling too much off. That's not a practice I would recommend.
 
Hoogah said:
I've just been through this issue while having the bottom of my motor rebuilt. My block had previously been bored out to the max (0.125") and decked quite severely. It had compression of 80 +/- 2 psi all round. The rebuilder said that the pistons were coming out of the block at the top of their stroke and fouling the (standard bore) head gasket. His solution was to take a chamfer off the top edge of the pistons.

Haven't re-installed it in the car yet.
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Was it the Best kryptonite or whatever it is?

http://www.secretsofspeed.com/gaskets.htm
Supposed to be good for four inches.
 
tinkirk, with head gasket installed.

Hoogah, Racers in the old days would bore their blocks to .187" oversize, although most stopped at .125", which works well. I don't recommend going more than 4", which is .125" over.

To all, I wouldn't mill off any more than just enough to touch the area above the pistons. Stock heads aren't very thick, and you no longer gain much compression. Stock pistons aren't very thick either, so use caution there.
 
I had a Model "B" head milled 0.090" which left about 0.010" depth of the piston pockets, and 0.03" clearance to the pistons. The compression increase was not competitive with a 5.5:1 cylinder head.



Occasionally, carbon buildup on the pistons would cause a horrible knock as it hit the head.


It is difficult to set the head up for milling such that the remaining material from the deck surface to the piston pockets are equal.


I would not do it again!
 
When milling the model B or C heads a person needs to be careful not to get carried away .The B and C heads have a concave area on the valve side of the head . If too much material is removed you will enter the concave area and the head won't completely cover the head gasket on the valve side of the engine. If the gasket is exposed to the combustion chamber the gasket will fail quicker on the exposed area . After milling , lay the gasket on the head to see how much of the gasket will be exposed . The engine will still run if part of the gasket is exposed to the heat of the combustion chamber but probably not as long as it would otherwise . I wouldn't have a B or C head milled any more than is necessary to level the head . It would be a shame to ruin A police head with the large letter B . Take a look at the recessed area on the valve side of these heads and you can see what I mean . The recessed area on these heads was Fords attempt to prevent valve shrouding on the manifold side .
 
I would worry about the water jackets becoming too thin and cracking as shown in the picture of a Model A police head. I would also worry about the pistons hitting the head once the recess had been removed (as in the photo). If I wanted compression I would buy a high compression aftermarket head. In my opinion, the less you mill the better, what are you starting with?

Charlie Stephens
 

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On original parts, it's anyone's guess as to what has been previously removed. This actually the Question that begs an answer before any surfacing process. A new head would eliminate 1/2 of the unknown, actually more than 1/2.
 
I am just wanting to true up the head not looking for compression increase. Just had the head tested for cracks, boiled and milled and it still has a .090 ridge so by what everyone posted there is nothing to worry about. I have learned a lot by reading your posts. Thanks guys
 
I have often thought about this! I have an original, untouched (I believe) head and I've wanted to check it with a depth mike and see just how thick it was. I'm sure that Henry must have had a standard thickness. If anyone knows what that dimension might be, please tell us.
Terry





100IH said:
On original parts, it's anyone's guess as to what has been previously removed. This actually the Question that begs an answer before any surfacing process. A new head would eliminate 1/2 of the unknown, actually more than 1/2.
Click to expand...
 
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