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Old 10-02-2019, 11:51 AM   #1
Vanspeed
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Default Cutting domes in 21 stud aluminum heads?

I have a pair of aluminum 21 stud factory heads but they are flat. My engine is a 36 LB and it has dome pistons. Is there enough material in the heads to cut the dome that is in my cast iron heads? Anybody done this?
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Old 10-02-2019, 12:39 PM   #2
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Default Re: Cutting domes in 21 stud aluminum heads?

That's a good question. I have a similar situation but, my engine has to be bored so, I'll use flat tops for it.

First, put the heads on it w/o a gasket and no nuts or use a straight edge, to begin with. Turn the engine over and see if it raises the heads. If not, you may be good to go (the dome is slight in my engine and you'll have about .040 deck clearance) as the head gasket on my Victors is .060 compressed.

If it does raise or touch the head, put one or two gaskets on and some small pieces of wadded tinfoil (held in place with grease) on top of all the pistons, as Ol' Ron suggests and turn the engine over, two times and measure it. You'll need that info, regardless.

From there, you'll be able to determine what needs to be done. You need a bare minimum of .035 clearance and if you only need about .030, you can have the dome cut, in a lathe. If you need much more, it will have to be done with a radius cutter, on the head or you will need to replace the pistons, with FH's.

Based on my engine (.040 over and I don't know the brand of the pistons), I think you would only need to cut no more that .040, from the head, if you have to and the head would be ok with that. Keep in mine, that there is also a .070 head gasket, to help with juggling these dimensions.

Last edited by frnkeore; 10-02-2019 at 12:46 PM.
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Old 10-02-2019, 03:23 PM   #3
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Default Re: Cutting domes in 21 stud aluminum heads?

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Originally Posted by Vanspeed View Post
I have a pair of aluminum 21 stud factory heads but they are flat. My engine is a 36 LB and it has dome pistons. Is there enough material in the heads to cut the dome that is in my cast iron heads? Anybody done this?
An ultrasonic test will give you the best answer.

A bit of trivia. Flathead race engines that develop over one hp per cubic inch naturally aspirated use flat top pistons and flat no dome heads.
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Old 10-02-2019, 03:34 PM   #4
Terry,OH
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Default Re: Cutting domes in 21 stud aluminum heads?

Seen it done and there was not enough meat at all four positions. It can be done with flat cast iron heads.
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Old 10-02-2019, 06:12 PM   #5
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Default Re: Cutting domes in 21 stud aluminum heads?

Yes, I'd change the pistons. These heads are hard to find.
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Old 10-03-2019, 12:08 PM   #6
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Default Re: Cutting domes in 21 stud aluminum heads?

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An ultrasonic test will give you the best answer.

A bit of trivia. Flathead race engines that develop over one hp per cubic inch naturally aspirated use flat top pistons and flat no dome heads.

Thanks for that, I suspected flat was better but couldn't get a clear answer on that. What deck clearance is minimum there?
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Old 10-03-2019, 01:47 PM   #7
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Default Re: Cutting domes in 21 stud aluminum heads?

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Thanks for that, I suspected flat was better but couldn't get a clear answer on that. What deck clearance is minimum there?
.040.

In the interest of economy if you already have domed iron heads, I would run those and just paint them aluminum if you like that color. Saves buying a set of pistons. You will never feel the hp difference in the seat of your pants in a street engine.
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Old 10-03-2019, 02:52 PM   #8
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Default Re: Cutting domes in 21 stud aluminum heads?

Pete,
Are you talking deck clearance or piston to head clearance?
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Old 10-03-2019, 03:41 PM   #9
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Default Re: Cutting domes in 21 stud aluminum heads?

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Pete,
Are you talking deck clearance or piston to head clearance?
Piston to head.
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Old 10-03-2019, 05:06 PM   #10
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Default Re: Cutting domes in 21 stud aluminum heads?

From what I see on ebay and HAMB, heads for dome top pistons with either 48 or 68 part number prefixes aren't scarce.
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Old 10-03-2019, 06:54 PM   #11
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Default Re: Cutting domes in 21 stud aluminum heads?

My stocks heads have a slight dome so I will take them in with the aluminum set and see what they say.
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Old 10-03-2019, 07:23 PM   #12
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Default Re: Cutting domes in 21 stud aluminum heads?

Good thinkin'.
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Old 10-03-2019, 10:02 PM   #13
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Default Re: Cutting domes in 21 stud aluminum heads?

Ive been there and tried that! I was too cheap to have them sonic tested, and ruined a NOS pair of hard to find heads. They now reside above a doorway in my shop so that I can blurt out a few curse words every time I walk under them, in remembrance of my mistake.
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Old 10-04-2019, 02:35 AM   #14
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Default Re: Cutting domes in 21 stud aluminum heads?

Quote:
Originally Posted by DavidG View Post
From what I see on ebay and HAMB, heads for dome top pistons with either 48 or 68 part number prefixes aren't scarce.
Being that the original poster said he has aluminum heads but want's to cut down iron.

Aluminum 21 stud heads aren't dropping out of trees. Well not any trees I know anyway.

h&h did a few runs on finned aluminum 21s with the heads up front. about $1,200, if you could get them. Maybe that's changed. But only current source I know.... that may not exists anymore.




Guess maybe an option..

"The Eddie Meyer 21 Stud Cylinder Heads are made to fit the 1932-36 Flatheads. They are for flat top or dome pistons (please specify when ordering). The are manufactured in the USA. 8.25 to 1 compression ratio."
https://handhflatheads.com/?s=21+stu...ct&dgwt_wcas=1





.

Last edited by Tinker; 10-04-2019 at 03:03 AM.
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Old 10-04-2019, 08:50 AM   #15
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Default Re: Cutting domes in 21 stud aluminum heads?

I have the smooth domed heads in stock. H&H Flatheads. Call 818-248-2371
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