Piston protrusion

D

doa44green

Member
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!
 
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.
 
doa44green said:
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!
Click to expand...

Not necessary on stock head unless it has been milled until there's no counterbore left. as long as the counterbore is .030 deep it will work with a standard gasket.

Bill
 
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 .
 
The area between the piston at TDC and the head is called 'quench', ideal quench is .040..best way to measure it is with a piece of modeling clay on the piston at TDC and torque the head down with gasket,remove and measure the clay.Stock A head is relieved and most gaskets run about .070 crushed.so the normal protrusion with a stock head isn't an issue..non relieved high compression head is a different story.
 
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.
 
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.
 
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