chaos.lrk.ar.us!dave.williams (Dave Williams)
hotrod  09 Sep 1993
- Now that multipart ceramic/aluminum pistons are no big deal (Isuzu
  Diesels have been using them for years) and coatings have improved to
  where they usually stay in place, a big two stroke might be practical now.
- I've also wondered if cast iron pistons might make a comeback.  Modern
  nodular-style irons are stronger than aluminum to start with and lose
  practically no strength at temperatures that would let you pour an
  aluminum piston out of your shoe.  With die casting instead of sand
  casting, you could probably come up with a nodular piston weighing
  little if any more than aluminum, more thermally stable, and able to
  laugh at lean mixtures and detonation.  Even if you couldn't equalize
  the weight, it'd be worth losing 1000 RPM or so if you could REALLY
  screw up the boost.
- [Even better would be a forged piston made from one of the exotic alloys.
  Way back in the early 70s one of my cousins was a big wheel metallurgist
  manager in the Army Missile Command at Redstone.  He made me a couple of
  experimental pistons, one out of titanium and the other out of some
  exotic stuff called Maraging 300.  This stuff hardens up to C60 rockwell
  and yet stays very ductile and has a yield strength of 300,000 psi.
- Anyway, the titanium piston worked but had problems of crown erosion.
  I suspect a ceramic coating would solve that problem.  The maraging
  piston was Wonderful!  Very thin-walled and lighter than the cast
  piston it replaced, it laughed at detonation and leanness.  Even when
  the engine was run lean enough to cause it to stick, the stick was
  temporary and any damage was to the cylinder wall.  He never did tell
  me how he made the piston, though he did say it was the same process
  used to make the combustion chamber in the Sidewinder missile.  It
  looked forged.  Hehehe, and you thought $600 toilet seats were bad :-) JGD]

[email protected] (Dave Williams)
mc-chassis-design  11 Apr 1998
- -> The properties of Beryllium that make it very cool for pistons are it
  -> high temp strength (2x Al), stiffness (5x Al), and low thermal
- Someday someone will realize cast iron is an excellent material for pistons 
  in two strokes.  One of the ductile iron alloys, investment cast and/or CNC 
  machined to remove excess bulk, would result in a piston of approximately 
  the same weight and strength as the typical aluminum piston. 
- The difference is the aluminum piston starts to get mushy around 1100F; the 
  iron one needs to be twice as hot before you worry about it.  You'd probably 
  melt the cylinder head before the piston was unduly distressed. 

[email protected] (Dave Williams)
diy_efi  24 Jan 1999
- -> a carbon-carbon piston does not need rings because of negligable
  -> [1/40 of Al] heat expansion.
- Sure.  Same with a properly designed and fitted cast iron piston. However, 
  the tapered skirt at the bottom and rings on the top dramatically reduce 
  cylinder wall friction.