Cylinder Head Flatness

[Bob Bidonde]

How much is the maximum usable run-out of flatness across the length and across the width of a cylinder head?

[Purdy Swoft]

Three thousands .

[Patrick L.]

Yep, and .002" width

[Bob Bidonde]

Purdy & Patrick,


Thanks for your replies.



The cylinder head is somewhat flexible and it clamps-up on a compressible gasket, so I suspect that the usable run-out of flatness can be more.


0.003" & 0.002" are what I would expect on a new head or one that is fresh out of a machine shop.



My intuitive thought is that 0.010" along the length and 0.005 across the width of a used cylinder head can be run successfully.

[Jim Brierley]

.006" is acceptable to my way of thinking, that's the guide we used when I was working on trucks.

[Railcarmover]

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Given the low clamping force Id be leery of .010..

[Bob Bidonde]

Railcarmover,


You make a good point that the clamp-up force is low for the amount of torque (50-55 lbs-ft). The chart is from a study I found online. Note how little of the torque goes to clamp-up.


I have installed many used stock cylinder heads, and not once did I have one resurfaced. I never measured the run-out of flatness of any of the used heads. To date, I have experienced gasket burn-throughs between Cylinders 3 & 4, but these were from using big-bore gaskets. The only other issue I've had is leakage from a new technology synthetic gasket with a new 5.5:1 head.


I am hoping that a Model A'er or two who have measured and used a head with a significant run out will share their experiences with us.

[Patrick L.]

The head could have been cut and installed by now.

[Pete]

Originally Posted by Bob Bidonde

How much is the maximum usable run-out of flatness across the length and across the width of a cylinder head?

Depends on how much you are willing to gamble on doing the job over.

I use zero, just like the factory.
There were no leaks or problems when they were new.

[Tom Wesenberg]

I'd want .002" or less across the width, and .004" or less along the length, and set .003" and .006" as the outer limits.
Remember, there is a lot of distance between the studs, beside the low clamping torque.

[rotorwrench]

Folks have to remember that the decks also have some flexibility in places. The more warpage the head has, the more it forces warpage into the deck. When head warpage is relatively easy to correct, I wouldn't see a good reason to leave it that way. If the head has been shaved too far, get a better used head or get one of the new ones.