Shaving a Standard Head

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pbishop

Senior Member
Generally speaking, what is considered to be the minimum head thickness safely allowable for the Model A head? As the amount of stock that may already been removed is not known to me, is a measurement form the bottom of the head to the top of the spark-plug bosses the measurement to take? If so, what is that factory measurement?
Or, is there another measurement to use?

Thanks for any advice
 
Thanks - I am looking at the valve clearance as a concern, as these will reach the highest extension up from the top of the block.
 
If you are doing this to raise compression, forget it. It won't make enough difference to matter, so just buy the 5.5 head.
 
Its the distance from the top of the piston with a head gasket on to the recess in the head over the piston that counts. Should be no less than .060
Other than that you can take off what ever you want.
5.5 or 6-1 is the way to go though.
 
It is not a good idea to ask the question re how much can be shaved. There needs to be an adequate amount of remaining pocket in the head for piston clearance. So the correct question is, "What is a workable piston to head clearance?"

Pistons will protrude above the cylinder block deck, especially on engines that have been professionally rebuilt because of machining the deck, and because of the brand of pistons used.

I had a head cut so the remaining piston pockets were 0.010" deep. A check with clay on the pistons using a copper head gasket indicated that the piston clearance was barely adequate (0.02" - 0.03"). Carbon buildup caused a scary loud knock.

I have since replaced the cut head with a 5.5:1 cylinder head, and the performance gain far exceeds the cut head.
 
Yes on the clay method. Shops that are meticulous, might stamp somewhere the amount that they took off but no one could say if there previous surfacing jobs. The method you describe, of measuring at the sparkplug gasket surfaces would require lots of setup time but no spec. and would require measuring setup that shops would normally not have. The cost of getting the measurement would be more $$ than the surface job. Usually, the surfacing removes only about .007 - .010. Most heads have probably been done two or three times before. Verify acceptable clearance and move on. If your lucky, the head has a hidden crack in the bore for one of the studs and you can get a quality new head and not worry any.
 
FWIW:

In our area, about 60 years ago, I always heard our old local machinists remark that the standard head shaving to slightly increase compression was to remove 3/16" from a "new" Model A head.
 
H. L. Chauvin said:
FWIW:

In our area, about 60 years ago, I always heard our old local machinists remark that the standard head shaving to slightly increase compression was to remove 3/16" from a "new" Model A head.
Click to expand...
I once took .075" from a Model A head, NOTHING CLATTERED:D
NEVER heard PINGING:D
Bill Fast?
 
I have a stock head with .040 off it and it has a little more compression and runs a little better. I also have an engine with a Snyder's 5.5 that runs a lot better. I've always heard that you could take .125 off a stock Mod A head with no problems. However, certain parts of the head are starting to get thin. I wouldn't do it. Try a "Snyder's", Oh and by the way, I'd get my Fly wheel lightened and balanced. And a "B" carb. and a bored out intake manifold. That should give you close to 50 hp, a very noticable difference! Google Pirianos Mod A.
Terry
 
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pbishop said:
Generally speaking, what is considered to be the minimum head thickness safely allowable for the Model A head? As the amount of stock that may already been removed is not known to me, is a measurement form the bottom of the head to the top of the spark-plug bosses the measurement to take? If so, what is that factory measurement?
Or, is there another measurement to use?

Thanks for any advice
Click to expand...

I took the max so I just had enough for the piston to not hit at high RPMS.
It did not help that much. The combustion chamber is a lot better on the 5.5 and 6,0 head. You are better off buying one of them.
 
Over on the V8 forums they say they want .050 of clearance for proper "quench area". Don't really know what that means yet... does it apply to the 4-banger as well?
 
Art Newland said:
Over on the V8 forums they say they want .050 of clearance for proper "quench area". Don't really know what that means yet... does it apply to the 4-banger as well?
Click to expand...

yes, it does.

The squish area is the flat area directly over the top of the piston.

Too little clearance and the piston may hit, too much clearance negates the turbulence generated to aid in reducing the detonation.

In the stock "A" head, you would be into the water jackets before the valves would contact the head.
The stock head is a very good design for the time it was designed, as normal, technology will cause shifts in the theory of design along with improvements.

If you want better performance, beg, borrow or steal a higher compression head, don't try to machine a stocker.

J
 
johnneilson said:
yes, it does.

The squish area is the flat area directly over the top of the piston.

Too little clearance and the piston may hit, too much clearance negates the turbulence generated to aid in reducing the detonation.

In the stock "A" head, you would be into the water jackets before the valves would contact the head.
The stock head is a very good design for the time it was designed, as normal, technology will cause shifts in the theory of design along with improvements.

If you want better performance, beg, borrow or steal a higher compression head, don't try to machine a stocker.

J
Click to expand...

John, I know a guy that mills every head he comes across. Then some times has to run two head gaskets. :confused: Reason being????????????????
I wish I knew. He wanted to sell me a 5.5 head that he milled and now said it was a 6.1. Really? :confused: I bought a 6.1 from Snyders for the same price he wanted for his. But hey. Cant blame him for trying to make a buck or two.:rolleyes:
 
Some logic never ceases to amaze me, having two gaskets just exaggerates the deck problem more and more.

Oh well, to each his own.

J
 
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