Model A head thickness

[Mike Kelley]

I have a police head. Plan to have it machined for flatness. What I do not know is how much metal has been machined off of the head in the last 80 year. Is there any way of determining how much the thickness of the head has been reduced since it was manufactured. I do not want to machine the head to a point that may weaken it.

Thanks,
Kelley

 

[Purdy Swoft]

My notes say that the unmilled thickness of the original head is 394 Measure the thickness of the casting from the underside in the edges of the water jacket holes near the distributor and the stud holes 4 and 5

 

[Aerocraft]

I suspect that the bosses where the studs go through on the Police head were the same height as a stock head. Could you come close to the amount removed from your head by comparing what you have to a stock head? Gar Williams

 

[Marco Tahtaras]

Ford used the largest possible fractional increment possible on virtually everything. That means that even inches (1" or 2" , etc.) would be used where possible, with 1/2" increments as the next choice and graduating down from there. I mention this because it applies to so many questions posted here but when you achieve the mindset you can often figure it out without asking.

Ok, now to address the actual question. The thickness of the head at the stud hole bosses was originally 2-1/4" or 2.250". The counterbore (flat recessed area of the combustion chamber) averaged 3/32" or approximately .093" deep from the machined surface. The first measurement can be reduced slightly from the head nuts chewing it down. The second can vary slightly from bringing the combustion chamber into spec. The combustion chambers were specified to be within 3 cc volume.

The pic below is one of my police heads while measuring the chambers. It was believed to be never surfaced but MAY have been lightly skimmed. Look closely at the series of numbers written on the surfaces. Near the stud holes are the thicknesses at each hole. The numbers within the counterbore are the depth of the counterbore at that particular point.

I should also add that I'm running a police head that I've had surfaced at least twice in 35 years bringing the cc down from 183 to 171 and it runs great. If I recall correctly there is has been about .035" removed.