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Old 04-28-2020, 05:02 PM   #1
Werner
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Default Lower cylinder head

Hi,

does it make sense, to plan the cylinderhead about 0,4 inch lower to get a little bit higher compression?

Thanks at all in advance for every hint.
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Old 04-28-2020, 05:40 PM   #2
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Default Re: Lower cylinder head

Werner, I think you mean plane the head by 0.04" (1mm). In a model A, the piston rises above the deck of the block. If you were to lower the head that much, you might have he piston hit the head. I'd tread very carefully with that.
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Old 04-28-2020, 05:48 PM   #3
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Default Re: Lower cylinder head

As mentioned, be careful about clearance between piton top and head surface. Also, you really won't gain much compression because the combustion chambers are so big. You'll be far better off getting an aftermarket high compression head.
A Model A "high compression" head is not that high! Stock is 4.2 and aftermarket ones are only around 5.9 to 1; some are 7 to 1. Yet, they are a huge improvement.
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Old 04-28-2020, 05:50 PM   #4
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Default Re: Lower cylinder head

Guten aend, Werner.
There are folks on this board mush more experienced than I am, but they all seem to be helping with your rod problem.
You asked about planing, or milling, the cylinder head 0.4 in to increase compression, but that is an excessive amount. It is common for Model A pistons to come up above the bolck surface by 0.040 inch, and milling 0.40 off the head woud cause the pitons to hit the head. It is common to plane the head just enough to assure it is truly flat, but more, and the squish area should be measured with clay.
There are several heads available with higher compression available in the catalogs. Good luck with your A!
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Old 04-28-2020, 06:52 PM   #5
Purdy Swoft
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Default Re: Lower cylinder head

Shaving or milling the original head won't help all that much .Its not just the compression ratio that makes the difference . The shape of the combustion chamber has a big effect . In 1932 Ford used the improved heart shaped combustion chamber on the four cylinder engines . though the improved head with the large C only produced 4.6 compression ratio , it added nearly seven horse power . The larger intake ports , improved camshaft lobe profile , intake manifold and larger carburetor added the additional three horse power for the model B engine . The C head will help some but not nearly as much as the police head with the large letter B will add . The compression ratio of the model A police head is 5.2 .

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Old 04-28-2020, 07:33 PM   #6
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Here's the business side of an A head..you can see where milling wouldn't remove much combustion chamber volume
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Old 04-28-2020, 07:38 PM   #7
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Here's the business side of a Snyder 5.5 to 1,this one was a reject,decked true.See how much shallower the combustion chamber is?This is a direct copy of Ford engineerings 1931 'Police' head.
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Old 04-29-2020, 07:39 AM   #8
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Default Re: Lower cylinder head

Many thanks to everyone for the helpful and particularly interesting tips.

I understood the risk and I am leaving the cylinder head like as it is.
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Old 05-02-2020, 01:56 PM   #9
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Default Re: Lower cylinder head

Guten Abend!

Is there a measure of the original height and the minimum for the cylinder head?
I have to let the head grind flat because the surfaces are very bad with rust blowholes

Thank you!
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Old 05-03-2020, 01:50 AM   #10
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Default Re: Lower cylinder head

Hi Werner, ich würde mir da nicht allzusehr Gedanken darüber machen, wieviel geplant wird. Das weiß der Motorenbauer sehr gut. In der Regel werden nur 1-3/10tel geplant. Weiterhin besteht auch die Möglichkeit, die Kolbentaschen nach dem planen um das gleiche Maß tiefer zu fräsen. Man kann das nicht unendlich oft machen, aber 1x würde sicherlich gehen. Ist nicht die feine Englische Art, aber eine praktische Lösung. Alternativ kann man auch mit dickeren Zylinderkopfdichtungen arbeiten, um das Maß wieder auszugleichen. Aber da wird dich der Motorenbauer bestens beraten.


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Old 05-03-2020, 10:21 AM   #11
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Default Re: Lower cylinder head

Wunderbar
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Old 05-03-2020, 12:43 PM   #12
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Default Re: Lower cylinder head

DRG, bevor ich den Kopf planen lassen kann, muß ich das Mindestmaß kennen. -


at all:

Nobody knows what's the minimum head height?
Or are there no factory specifications? I studied Mcree, Andrews, the Service Bulletin and the manual. But nowhere found a number that specifies a minimum height.
The level is warped by 0.004 ". There are also aprox. 0,01 deep rust holes on the sealing area too.
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Old 05-04-2020, 10:35 AM   #13
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Default Re: Lower cylinder head

Quote:
When milling the head you first have to measure how far the pistons rise above deck height at top dead center. Originally the pistons rose about .030 to .032 . Here is how to figure. If using the copper gasket, they will usually compress to a thickness of around .050 after being torqued. That puts the top of the piston .018 below the top of the gasket if the pistons are rising .032 above deck height. If the head is milled until the counter bore above the piston has a depth of .030, this will give .048 clearance between the head and the top of the piston and this is actually more clearance than is necessary but allows for heat expansion and high rpm reach. You could get by with .030 clearance between the piston and the head after figuring the thickness of the compressed gasket. If you didn't exceed 3000 rpm.
Borrowed from: http://pvmafc.org/phpbb/viewtopic.php?f=35&t=6610
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Old 05-04-2020, 02:55 PM   #14
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Default Re: Lower cylinder head

Hello and good evening Katy, special thanks for your good advice.
If I understand that correctly, the head gasket is always thicker than the cantilever of the piston. So grinding my head is not a problem.
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Old 05-15-2020, 03:39 PM   #15
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Default Re: Lower cylinder head

Hallo, here are now a few measurements that are perhaps sometimes helpful to others:

The grounded/planed cylinder head height is 94.5 mm up to the "goose"-flange.

The modern head gasket with silicone inserts has a height of 2.2 mm.

The combustion chamber depth in the head is 1.4 mm.

The piston showes 0.6 mm beyond the block over.
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Old 05-19-2020, 04:37 PM   #16
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Default Re: Lower cylinder head

Guten Abend.
Is it really true that the thick copper-clad seal under the goose neck can lead to breakage? Because of the great screwing power for the head? And therefore only a thin paper seal should be underlaid?
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Old 05-19-2020, 05:24 PM   #17
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Default Re: Lower cylinder head

Quote:
Originally Posted by Werner View Post
Guten Abend.
Is it really true that the thick copper-clad seal under the goose neck can lead to breakage? Because of the great screwing power for the head? And therefore only a thin paper seal should be underlaid?
Werner, I use no gasket at all. I use either a layer of Permatex #3 or a light smear of silicone. I've never used a gasket and never had a problem with that.
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Old 05-20-2020, 05:42 PM   #18
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Default Re: Lower cylinder head

Guten Abend,
thanks for the hint. I cut a thin cardboard gasket myself today because the surface on the enginebloc was very scarred and I glued it with a thin lay of silicone rubber.
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Old 05-21-2020, 11:06 AM   #19
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Default Re: Lower cylinder head

Quote:
Originally Posted by Werner View Post
Guten Abend.
Is it really true that the thick copper-clad seal under the goose neck can lead to breakage? Because of the great screwing power for the head? And therefore only a thin paper seal should be underlaid?
I used a copper gasket on the goose neck when assembling my engine 8 years ago.The next day I was in my shop and heard a loud bang noise over by engine .Went over to see what it was and found the goose neck had cracked.
I use only silicone now and it works without any leakage. Dennis
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