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Old 06-14-2019, 11:53 AM   #1
Bob Bidonde
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Default Cylinder Head Flatness

How much is the maximum usable run-out of flatness across the length and across the width of a cylinder head?
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Old 06-14-2019, 12:05 PM   #2
Purdy Swoft
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Default Re: Cylinder Head Flatness

Three thousands .
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Old 06-14-2019, 12:59 PM   #3
Patrick L.
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Default Re: Cylinder Head Flatness

Yep, and .002" width
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Old 06-15-2019, 08:06 AM   #4
Bob Bidonde
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Default Re: Cylinder Head Flatness

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.
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Old 06-15-2019, 10:17 AM   #5
Jim Brierley
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Default Re: Cylinder Head Flatness

.006" is acceptable to my way of thinking, that's the guide we used when I was working on trucks.
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Old 06-15-2019, 11:02 AM   #6
Railcarmover
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Default Re: Cylinder Head Flatness

Given the low clamping force Id be leery of .010..
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Old 06-15-2019, 11:29 AM   #7
Bob Bidonde
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Default Re: Cylinder Head Flatness

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.
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File Type: jpg Bolt Torque Distribution Pie Chart.jpg (12.7 KB, 33 views)
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Old 06-15-2019, 01:16 PM   #8
Patrick L.
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Default Re: Cylinder Head Flatness

The head could have been cut and installed by now.
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Old 06-15-2019, 01:49 PM   #9
Pete
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Default Re: Cylinder Head Flatness

Quote:
Originally Posted by Bob Bidonde View Post
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.
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Old 06-15-2019, 08:18 PM   #10
Tom Wesenberg
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Default Re: Cylinder Head Flatness

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.
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Old 06-16-2019, 09:12 AM   #11
rotorwrench
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Default Re: Cylinder Head Flatness

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.
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