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07-15-2020, 07:31 PM | #1 |
Junior Member
Join Date: Nov 2016
Posts: 25
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Piston protrusion
According to Les Andrews, page 1-81, if the pistons protrude above the block surface a .100 thick head gasket should be used. Where can I find one, and is this really necessary?
Thank you for any input! |
07-15-2020, 09:36 PM | #2 |
Senior Member
Join Date: May 2010
Location: Campbell,CA, USA
Posts: 333
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Re: Piston protrusion
If all dimensions are nominal (new from factory), the pistons are designed to protrude 1/32 inch (.03125 inch) above the top surface of the cylinder block.
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07-16-2020, 02:23 AM | #3 | |
Senior Member
Join Date: May 2010
Location: Yakima Washington
Posts: 913
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Re: Piston protrusion
Quote:
Bill |
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07-16-2020, 04:38 AM | #4 |
Senior Member
Join Date: May 2010
Posts: 1,306
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Re: Piston protrusion
I recently fitted a new head gasket . When I rotated the engine I could feel that the pistons were contacting the gasket edge . The engine is +100 and came with a regular unplaned head. The pistons are about 25 thou proud of the deck .Investigation revealed that the new head gasket edge entered the combustion chamber . I then tried to find a gasket which does not do this . I found a used "Flag 7013" which could be used I think it seems to have more "room" around the combustion chambers . The engine came with a loose head no gasket I just wondered if there is a special gasket tailored to suit the +100 overbore and 25 thou protrusion ???
John in Suffolk County England . |
07-16-2020, 08:12 AM | #5 |
Senior Member
Join Date: May 2010
Posts: 2,623
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Re: Piston protrusion
John,
Here is Best Gaskets webpage Vintage Engine gaskets. https://bestgasket.com/vintage-engine-gaskets/ They also make CUSTOM gaskets. You can find a link on the page above Fel Pro makes a gasket 7013 Version R4 is for over size bores as I remember. Better yet check out Vince Falters info on Fordgarage.com. As always .. most helpful. http://www.fordgarage.com/pages/ABcy...asketguide.htm Last edited by Benson; 07-16-2020 at 11:53 AM. |
07-16-2020, 08:24 AM | #6 |
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Re: Piston protrusion
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07-16-2020, 08:28 AM | #7 |
Senior Member
Join Date: May 2010
Location: Long Island, NY
Posts: 3,550
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Re: Piston protrusion
Do a clay test. Put a lump of clay on top of each piston, install the cylinder head and hand -crank the engine. Remove the head and measure the thickness of the clays. In my opinion, the clays should be 0.09" thick or more.
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Bob Bidonde |
07-16-2020, 09:04 AM | #8 |
Senior Member
Join Date: Aug 2010
Posts: 260
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Re: Piston protrusion
Last week I milled a stock head to the fly cut then removed all traces of the fly cut ( .125"). the old gasket measured .070" thick, The new BEST gasket measured .080" new. On this forum it has been said you need .035" to .040" clearance between piston and head. I disagree with Les Andrews. All pistons protrude 1/32". Most all rebuild kits have a copper gasket that measures approximately .080".
My compression went from 70 psi to 80 psi in all cylinders. I fell the improvement when accelerating. |
07-16-2020, 09:45 AM | #9 |
Senior Member
Join Date: May 2010
Location: Alabama
Posts: 8,099
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Re: Piston protrusion
I believe that all of the model A pistons protruded just over thirty thousands above deck height when new .
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