Metal Working: Designing and Making Pistons

Learn the details of pouring, feeding and the solidification of iron and aluminum piston castings so you can do it yourself.

| December 2012

  • Alluminum's long freezing range alloy
    Iron pistons are easily cast by using small gates on the top edge of the casting and no risers. Aluminum pistons, because of solidification shrinkage, are more difficult to cast. Pouring temperature and the placement of gates and risers are very important. 
    Illustration Courtesy Chastain Publishing
  • Making Pistons book cover
    With the know-how provided in “Making Pistons” by Stephen Chastain, you are no longer limited by the price and availability of replacement pistons and rings. Design and build your own with this metal-working guide. 
    Cover Courtesy Chastain Publishing
  • Microshrinkage in castings
    Aluminum castings freeze by three different methods. In pure aluminum, shrinkage occurs as a deep pipe or at the centerline of the casting. Solidification of alloy #295, 94% aluminum, 5% copper, 1% silicon begins at the wall but progresses quickly to the center of the casting.  Fine grains form randomly in the center of the casting and freezing continues in a mushy state.  
    Illustration Courtesy Chastain Publishing
  • Good casting uses small gates and a low pouring temperature.
    The highest number of good castings results from using a combination of small gates and low pouring temperature. Gating Scheme 1: The gates must be no thicker than .6 the wall thickness. 
    Illustration Courtesy Chastain Publishing
  • Short Risers Gating Scheme
    A second and simpler scheme is to use very short risers and gate into the thin top section of the (inverted) casting. I recommend starting with this scheme.
    Illustration Courtesy Chastain Publishing
  • Piston Poured at 1200 degrees F
    Piston 2 is the same mold poured at 1200oF. 
    Photo Courtesy Chastain Publishing
  • Example of Gross Shrinkage
    Gross shrinkage is seen in piston 1. It was poured at 1350oF. 
    Photo Courtesy Chastain Publishing

  • Alluminum's long freezing range alloy
  • Making Pistons book cover
  • Microshrinkage in castings
  • Good casting uses small gates and a low pouring temperature.
  • Short Risers Gating Scheme
  • Piston Poured at 1200 degrees F
  • Example of Gross Shrinkage

Design and make pistons and rings for new or old engines with this must-have, heavily-illustrated guide for both beginner and experienced metal workers.  Making Pistons for Experimental and Restoration Engines (Chastain Publishing, 2004) by Stephen Chastain instructs on how to make the tools and jigs you need to quickly produce top quality replacements in your own back yard and home shop. Learn all about making pistons with this excerpt taken from chapter four, “Casting and Feeding.” 

You can purchase this book from the Farm Collector store: Making Pistons.

Making pistons: pouring, feeding and solidification of piston castings 

Pistons may be made of cast iron or aluminum. Iron pistons are easily cast by using small gates on the top edge of the casting and no risers. Aluminum pistons, because of solidification shrinkage, are more difficult to cast. Pouring temperature and the placement of gates and risers are very important.

Aluminum castings freeze by three different methods. In pure aluminum, shrinkage occurs as a deep pipe or at the centerline of the casting. Solidification of alloy #295, 94% aluminum, 5% copper, 1% silicon begins at the wall but progresses quickly to the center of the casting.  Fine grains form randomly in the center of the casting and freezing continues in a mushy state. The center of the casting may be as much as 85% solid before a completely solid skin forms on the surface. As a network of solid grains form, feed metal is unable to flow through the constricted passages and microshrinkage occurs around the dendrites. The riser height drops and distributed microshrinkage forms throughout the riser and casting.



Chills are used to force the metal to freeze quickly from one end before the network of grains forms, constricting the flow of feed metal. Chills also increase the mechanical properties by reducing the segregation of gas and impurities at the grain boundaries.

Many pistons are cast from alloy F 132, or  #332 (they are equivalent alloys). Alloy #332, silicon 9.5%, copper 3% solidifies with some gross shrinkage and some distributed microshrinkage.



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