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Thinner Head Gasket

Discussion in 'Tech' started by OGs750, Dec 16, 2008.

  1. ed who?

    ed who? the opposite of eharmony.

    close....ZUMA 450 :crackup:

    Your prize is on way..just gotta figure how much to insure "her" for thru UPS :)
     
  2. kneedragger29

    kneedragger29 Well-Known Member

    "Doers & thinkers" are exempt from low brow humor.
    :Poke: /Sorry
     
  3. epee

    epee Well-Known Member

    I need some help understanding this. Both statements imply that decking the head, decking the block, or head gasket thickness reduction will have different impact on the combustion chamber. Taking .010" off the head surface, the cylinder block, or using a .010" thinner head gasket all have the effect of bringing any reference point in the combustion chamber .010" closer to the crank centerline (and, therefore, the piston crown). The piston would come .010" closer to the squish area and .010" closer to any open valve (assuming no changes to valve timing). I would expect any method used to make the .010" reduction would have the same impact.

    I suspect that decking the head does have a secondary impact on combustion chamber shape, since you would presumably be slightly reducing the percentage of surface area projected below the concave portion of the chamber vs. the projection below the machined flat area (over the piston). This would seem to be a small difference, though. I really don't see how decking the block or reducing the head gasket thickness would give different results. (For this discussion, I'm assuming all components were straight to start with and we are only looking at the impact on the combustion chamber, not on component alignment, surface flatness, etc.)

    Obviously, I'm not an engine builder (at least for 4-strokes). But I am interested and would appreciate any further explanation.
     
  4. TWF2

    TWF2 2 heads are better than 1

    milling head does not change squish area.clearance stays same.
     
  5. epee

    epee Well-Known Member

    OK. I'm an idiot... Obviously, the clearance to the machined surface above the piston remains the same after milling head.

    Thanks. :up:
     
  6. Tim Radley

    Tim Radley Well-Known Member

    Exactly right, you can remove 2 inches from the head and the piston to head clearance would not change. Piston to head relates to the flat portion of the head only, ie the squish pads. Think about it.
     
  7. epee

    epee Well-Known Member

    I understand. The only engines I've seriously modified are 2-strokes, and that was a long time ago. Their squish bands were in the concave portion of the head, so milling the head did bring the piston closer to the recessed combustion area in the head.

    Sorry, I should think longer before posting! Thanks again.
     
  8. g.mccormick

    g.mccormick Well-Known Member

    Just remember even though it doesn't change squish/head clearance, it does change piston to valve clearance.
     
  9. TWF2

    TWF2 2 heads are better than 1

    I wonder if he asks what are valves :D
    two smokes don't have those.
     
  10. g.mccormick

    g.mccormick Well-Known Member

    Unless you count reed valves and powervalves. :)
     

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