Model A Head Torque (revisited)

BButturff

BButturff

Senior Member
I realize the “How to”, “When to”, “Which head gasket”, “Which torque patterns”, "Sealant/no sealant" and “Hot or cold” of torquing a Model A cylinder head have been discussed at great length in these forums. I've even read a couple of posts that covered how much better the head clamping force would have been if it had been designed with more studs. Additionally, I've read that higher compression aftermarket cylinder heads are recommended to be torqued to 60 ft/lbs (or more) for additional clamping force.


So here's my humble question. When we go to the expense of rebuilding an engine, why don't we install larger diameter head studs that can be torqued to a higher spec? Without knowing the facts it seems easy enough.
 
My question is: Is there enough material around the holes in both the block and the head for larger studs? I assume there would be enough in the head, but the block?
 
The issue in my opinion is not the size of the stud, it is the deck.
The deck is thin and the boss under the head stud does not provide much support
Many head stud holes have been enlarged to repair a stripped thread or worst a poorly performed broken stud removal

Additionally the cyl head is not rigid or stiff enough to withstand higher torque on the studs and the gasket provides a soft medium to allow for deck distortion

While this may sound discouraging it is possible to build for higher performance

Short of making a billet solid head, Jim Brierley offers an aluminum head that is much sturdier and seems to help in keeping gaskets in place with std head stud torque
Also the quality of the studs is very important

When building very high performance using a solid copper gasket or no gasket with orings is possible without increasing the fastener size

John
 
One trick that builders of high performance engines use is to use an insert in the block for the studs. The helical coil type inserts can be used in Model T and Model A blocks and add a considerable amount of pull out strength. It is equivalent to using a larger stud because the inserts are larger. Being spring steel, the inserts are also stronger than the cast iron so that the stud does not pull out of them. If you decide to add helical coil type inserts, use an old head as a drilling and tapping guide. Bolt the ends of the head down with two studs and nuts and then drill out the holes in the old head with the drill for the inserts. Put two studs in the new inserts and them repeat the process where the two studs were that held the head down.
 
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nkaminar said:
One trick that builders of high performance engines use is to use an insert in the block for the studs. The helical coil type inserts can be used in Model T and Model A blocks and add a considerable amount of pull out strength. It is equivalent to using a larger stud because the inserts are larger. Being spring steel, the inserts are also stronger than the cast iron so that the stud does not pull out of them.
Click to expand...


That's interesting because I have seen replacement studs that are a larger diameter at the thread that goes into the deck with the rest of the stud being stock dimensions. I suppose these type of studs would accomplish a higher clamping load like the Helicoil insert you mentioned.
 
Applying tightening torque is fundamentally inefficient as shown in the attached slide.
 

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  • Tightening Torque Distribution.jpg
    Tightening Torque Distribution.jpg
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Here's an interesting tidbit- the torque wrench was not used by Ford on the assembly line. Torque wrenches didn't come into widespread use until the late '30s. Ford used a wrench of an appropriate length so that the average man could tighten the head bolts sufficiently with a tug and a grunt.
 
As previous posts have alluded to, the limiting factor here is not the studs – modern studs can take a very high amount of force. The failure mode will be the threads in the block deforming in a way that reduces the clamp load at that joint. Reinforcing the threaded bores in some creative way will buy you a little increased clamp load, but eventually you run into the problem that the A block is designed with a relatively low number of attachment points for its surface area. Cast iron isn't infinitely rigid – if you put too much force at one point it'll warp, regardless of how big the threaded joint is. That's why later V8 blocks spread out the force over a larger number of bolts and a smaller total surface area.

It is also the case that the clamp load provided by the factory setup is adequate for combustion forces in a stock engine. You would have to be modifying the engine for higher compression and rpm to have any need for greater clamp load.
 
for the Model A the Best brand plain Graphite gasket with a little Copper Kote spray, torqued to 55# is excellent. Do one re torque after cooling overnight. its not complicated
 
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I will confer with Butch Chase, Post #10. The only thing I would add is to again retorque after 100 miles and 500 miles.
 
johnneilson said:
The issue in my opinion is not the size of the stud, it is the deck.
The deck is thin and the boss under the head stud does not provide much support
Many head stud holes have been enlarged to repair a stripped thread or worst a poorly performed broken stud removal

Additionally the cyl head is not rigid or stiff enough to withstand higher torque on the studs and the gasket provides a soft medium to allow for deck distortion

While this may sound discouraging it is possible to build for higher performance

Short of making a billet solid head, Jim Brierley offers an aluminum head that is much sturdier and seems to help in keeping gaskets in place with std head stud torque
Also the quality of the studs is very important

When building very high performance using a solid copper gasket or no gasket with orings is possible without increasing the fastener size
John
Click to expand...

I agree with John, it is the deck thickness that limits things. Having said that, I run ARP studs of stock size, and have Run Bonneville with as much as 10:1 compress and currently 7.5:1 and turbo charged, on alcohol with no gasket problems. My Cook OHV engine is cast iron and very rigid, but John runs an aluminum head, also quite rigid.
 
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