Piston to head clearance too tight?

Discussion in 'Engine Topic' started by Mwilson, Dec 6, 2017.

  1. Mwilson

    Mwilson Veteran Member

    My pistons are .006 out of the hole and my gaskets are .041 that only gives me .035 Anyone have thoughts ok not ok?
     
  2. Dave Nelson

    Dave Nelson Veteran Member Gold Member

    3,133
    373
    Dec 19, 2003
    Vineland N.J USA
    Have you mocked it up with a head to see what the piston to valve clearance is?
     
  3. Mwilson

    Mwilson Veteran Member

    I have Fel Pro 1003 .041 gaskets and the piston is .006 above the block deck


    24775033_1942234522763862_2006458597159042231_n.jpg
     
  4. Z28zz383

    Z28zz383 Veteran Member

    786
    4
    May 11, 2012
    Florida
    Install some weak springs on the cyl you want to check. put modeling clay in valve pockets. And a pc on piston top. Bolt on head w/o applying full tq value. rotate carefully by hand. Dis assemble and check the clay for verification of clearance. This the way I have seen it done.
     
  5. Mwilson

    Mwilson Veteran Member

    im not worried about valve clearance Im worried about piston-to-head clearance
     
  6. 70lt1z28

    70lt1z28 Veteran Member Gold Member

    1,275
    138
    Oct 3, 1999
    Beavercreek, Ohio, USA
    Should be fine. Unless you are running aluminum rods or 10000 RPM

    What you are measuring is the quench area. Should be 0.03 to 0.04. The factory had the piston in the hole by 0.025 and had a 0.015 steel shim gasket. This ends up at 0.04 clearance.

    It's actually detrimental to run much more than 0.04. The turbulence from good quench helps prevent detonation.

    If you do want a bit more you can always go to Cometic for some 0.05 gaskets.
     
  7. cadillac_al

    cadillac_al Veteran Member

    525
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    Apr 22, 2015
    Maine
    I don't know the exact "safety margin" that you need either but you are very close. I would be worried too until a pro engine builder told me he has done it before. I'm fairly sure it would be safe to 5k rpm but I'm sure you are planning for more than that.
     
  8. Mwilson

    Mwilson Veteran Member

  9. 70lt1z28

    70lt1z28 Veteran Member Gold Member

    1,275
    138
    Oct 3, 1999
    Beavercreek, Ohio, USA
    Assume then forged pistons. 0.040 to 0.045 would be best. 0.035 would be a minimum. Forged grow a bit more than hypereutectic and 7k is pushing it. If it was a grocery getter I would say again you are fine at 0.035. Is it too late to deck a few thou from the tops? Otherwise go to Cometic.
     

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