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Old 03-18-2018, 02:35 PM   #1
GOSFAST
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Default Checking Cyl Head Flatness

This is aimed more at aluminum heads that have been in service for a few years.

This is actually a (Canadian) head from a member here chasing an internal water leak. Got it for pressure test and "Zyglo".

You can see from the photo all the irregularities that couldn't easily be found with a "straight-edge" and a "feeler guage".

There are a couple of very visible "lows" and "highs" across the surface that shows up easily with a very flat table (Bridgeport) and an accurate dial indicator.

Thanks, Gary in N.Y.

P.S. Based on our experience and those "recorded" numbers written on the head surface it will require about .014" to make it flat again!
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Old 03-18-2018, 03:40 PM   #2
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Default Re: Checking Cyl Head Flatness

If I couldn't see the difference between zero at the ends and +9 in the middle, with a straight edge, I would throw away the straight edge. Or, maybe I am not reading the numbers correctly?
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Old 03-18-2018, 03:55 PM   #3
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Default Re: Checking Cyl Head Flatness

How do you hold it, and how do you measure it? do you clamp it to the table and run it under an indicator in the spindle by cranking the table, or use the table like a surface plate?

FWIW I've found most used Bridgeport tables are bowed.
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Old 03-18-2018, 04:17 PM   #4
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Default Re: Checking Cyl Head Flatness

That head looks good take a good flat file and just clean any burrs.
With all those bolts it will get pulled down.
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Old 03-18-2018, 04:35 PM   #5
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Default Re: Checking Cyl Head Flatness

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Originally Posted by George/Maine View Post
That head looks good take a good flat file and just clean any burrs.
With all those bolts it will get pulled down.

Your knowledge is amazing! DD
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Old 03-18-2018, 04:36 PM   #6
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Default Re: Checking Cyl Head Flatness

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Quote:
Originally Posted by JWL View Post
If I couldn't see the difference between zero at the ends and +9 in the middle, with a straight edge, I would throw away the straight edge. Or, maybe I am not reading the numbers correctly?
I like that comment.
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Old 03-18-2018, 04:56 PM   #7
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Default Re: Checking Cyl Head Flatness

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If I couldn't see the difference between zero at the ends and +9 in the middle, with a straight edge, I would throw away the straight edge. Or, maybe I am not reading the numbers correctly?

I would put my glasses on and then throw it out. "LOL"

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Old 03-18-2018, 07:02 PM   #8
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Default Re: Checking Cyl Head Flatness

Check piston to head clearance and mill for .050" clearance. And this will make them flatg
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Old 03-19-2018, 07:31 AM   #9
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Default Re: Checking Cyl Head Flatness

Check out this video. https://www.youtube.com/watch?v=SK2R2LdkLKs
Then do as Ol'Ron said "foil" to check clearances
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Old 03-19-2018, 07:34 AM   #10
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Default Re: Checking Cyl Head Flatness

Don't fuss with it...any automotive machine shop will resurface the sucker.
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Old 03-19-2018, 01:04 PM   #11
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Default Re: Checking Cyl Head Flatness

With aluminum, it can be lapped if you are just straightening it out but Ron has a point. If it needs less clearance with the piston then it needs to be milled anyway.

I use a big Starrett grave stone (granite surface plate) to check my stuff.
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Old 03-19-2018, 01:12 PM   #12
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Default Re: Checking Cyl Head Flatness

You can bend that head very easy. Try some plastic gage in center and outer edge.
The head looks good to me.
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Old 03-19-2018, 05:25 PM   #13
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Default Re: Checking Cyl Head Flatness

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You can bend that head very easy. Try some plastic gage in center and outer edge.
The head looks good to me.
Your complete understanding of, and your willingness to pass-on so much misinformation is to be commended. DD
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Old 03-19-2018, 07:56 PM   #14
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Default Re: Checking Cyl Head Flatness

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You can bend that head very easy. Try some plastic gage in center and outer edge.
The head looks good to me.
Yikes x 3

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Old 03-19-2018, 11:48 PM   #15
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Default Re: Checking Cyl Head Flatness

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Your complete understanding of, and your willingness to pass-on so much misinformation is to be commended. DD


I have been doing things like that for years and taking money from smart ass people like you DD DOO DOO Being in the machine trade helps to know what you can do.


My frist 51 ford flathaed i did in 1962 makeing $1 dallor hour.


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Old 03-20-2018, 12:47 AM   #16
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Default Re: Checking Cyl Head Flatness

I'm pretty sure Gary knows what to do .. he's just showing for interest.
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Old 03-20-2018, 06:57 AM   #17
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Default Re: Checking Cyl Head Flatness

George, You may have a point that would suffice in a pinch but if you try to straighten the head by torquing it down then force applied is straightening the head and not compressing the gasket. Also the numbers change at the very ends and do not show progression from the middle. When it's apart and the machine is available there's no excuse to do it any other way. Just my limited experience opinion.
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Old 03-20-2018, 07:42 AM   #18
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Default Re: Checking Cyl Head Flatness

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Originally Posted by Talkwrench View Post
I'm pretty sure Gary knows what to do .. he's just showing for interest.
Correct, first step here is heat (Bayco) and a tool made specifically for straightening "warped" aluminum heads.

This may help us get it somewhat closer to flat, then finish with a CNC mill.

Thanks, Gary in N.Y.

P.S. Under no circumstances would I try straightening a "cold" head. Can all but guarantee ending up with a cracked casting by the time it's "straight"?
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Old 03-21-2018, 04:23 PM   #19
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Default Re: Checking Cyl Head Flatness

I have thought of but never tried bolting two heads together then heating them and allow to cool slowly.
This thought came from a look at two new cast aluminum heads. Put face to face, I could see about .030" or .040" between them, at the center. I did not wind up buying, too much $ at the time.

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