what head gasket

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E

engine man

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hi putting closed chamber aluminum heads on a stock 70 340 with the factory positive deck pistons. i believe .018 out of the hole. what thickness head gasket should i run and its part number also it is 4.070 bore thanks ed
 
well...you would want about .035 piston to head clearance...with .018 positive deck....that would be about .053
 
The felpro 8553pt will not give the quench distance needed
 
Distance would be .028- .030 after gasket compression
 
.028-.030 should work fine unless you are using old fordgetrues with .008 clearance
want a thicker gasket check the Victor and McCord Marine lines
or Cometic
there are also inexpensive shims to use with the .028 or .040 gasket
 
As said:
  • The Felpro 8553PT's (standard Felpro kit gakets) will compress a varied amount.... their compressed thickness has been reported in this forum as little as .046".
  • And the nominal protrusion of the original 340 pistons are .018 but can vary with rod lengths, cranks, and deck height variations; numbers have been reported on this forum of as little as .010" and a much as .023".
So if you just estimate this, then you could end up with well under .030" and as little as .023" clearance... not nearly adequate. And if the pistons/bores are worn or forged units have been used with their larger bore clearance, then the piston rock will be worse.

So, OP, don't just put on an 8553PT gasket unless you measure every piston and how far it protrudes; use a dial indicator or feeler gauges.... you'll probably be surprised how much this varies. And check how much the piston height varies at top and bottom with rocking. With it being overbored, you don't know what is in there.
 
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