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Re: Oval pistons (was Re: s4 rough acceleration)

In a message dated 02/03/1999 1:49:39 PM Pacific Standard Time, ScottyCBoy
writes:

<< << The bit about oval pistons/bores is a description of what happens if you
  abuse an engine while cold.  A too-small piston in a too-large bore will
  rock back and forth (or side to side) under load, and this can wear
  either the piston, the bore, or both.  By the time one or the other is
  oval, the damage has already been done. >>
 
 Pistons are not machined round in fact they are oval, usually about 1 or 2
thousands out of round this is because the shape of the piston isn't uniform,
the material where the wristpin rides is much thicker than the material 90
degrees adjacent to it, therefore when the piston heats up the thicker
material portion will expand more than the thin area and this takes up the out
of roundness out, so the piston is round when at operating temperature. On air
cooled negines this out of roundness is more pronounced due to the fact that
there is a possibility of piston temps to be much higher than a water cooled
engine.
 
 Scotty >>



In a message dated 02/03/1999 1:43:26 PM Pacific Standard Time,
sefisher@cisco.com writes:

<< The bit about oval pistons/bores is a description of what happens if you
 abuse an engine while cold.  A too-small piston in a too-large bore will
 rock back and forth (or side to side) under load, and this can wear
 either the piston, the bore, or both.  By the time one or the other is
 oval, the damage has already been done. >>

Pistons are not machined round in fact they are oval, usually about 1 or 2
thousands out of round this is because the shape of the piston isn't uniform,
the material where the wristpin rides is much thicker than the material 90
degrees adjacent to it, therefore when the piston heats up the thicker
material portion will expand more than the thin area and this takes up the out
of roundness out, so the piston is round when at operating temperature. On air
cooled negines this out of roundness is more pronounced due to the fact that
there is a possibility of piston temps to be much higher than a water cooled
engine.

Scotty