Pistons

• The piston's primary responsibility is to take thermal energy created by the ignition of fuel and air, and transform it into linear motion. Linear motion acts on the crankshaft journal and becomes rotary motion.

A typical piston illustrating the various parts and the names.

Piston Heads (Crown)

• Domed• Flat Top• Recessed (valve reliefs)• Dished

A domed piston with valve reliefs or valve pockets.

A Flat Top piston

A Flat Top piston with valve reliefs or valve pockets.

A Dished piston with valve reliefs or valve pockets.

Piston Composition @ Process

• Aluminum - Forged– Can be made lighter weight

(smaller) than cast because it’s stronger

– Can withstand abuse– Newer designs have

predictable expansion qualities

– Silicon & Nickel added– Greater piston to wall

clearance

The Rod

• The piston begins as a three meter, solid aluminium rod. The reason aluminium is used is that it's lightweight, rust-proof, and easy to cut. A saw then cuts the rod into smaller pieces called slugs.

The Punch

• A punch press and dye are pre-heated while the slug moves through an oven, heating it to the same temperature as the punch press. The slug is then removed from the oven, and placed into the punch. The press applies 2,000 tons of pressure onto the slug, forging it into the basic shape of a piston. This process causes the piston to become so hot, that it needs an hour to cool down.

The Oven

• After the forgings cool down, they go through an oven twice more. The first time is at a higher temperature, to strengthen the metal. The second time is at a lower temperature to stabilize it.

The Lathe

• A lathe is then used to cut excess metal from the basic form of the piston, taking it closer to its finished shape. Then tiny holes are drilled in the sides, allowing oil to lubricate the piston when it's in use. The same lathe then impresses three rings into the top of the piston. These rings, or grooves, help the piston glide, and allow it to form an air-tight seal.

The Wrist Pin Holes

A large hole is then drilled through both sides of the piston. This is where the wrist pin will go, attaching the piston to the connecting rod.

The Milling Machine

• A milling machine then shaves up to a couple of centimeters off of each side of the piston where the large holes were drilled for the wrist pin insertion. This is to reduce the overall weight of the piston. Another milling machine takes some more metal off of the area where the three rings were formed earlier, bringing the piston one step closer to its final form.

Finishing the Job

• Another lathe shaves a few more millimeters off of the top, allowing the piston to expand when heat builds up inside of it. Then a machine engraves model and production information. A human worker then smooths out the sharp edges of the piston created during production. The holes created for the wrist pin are then put through a machine which smooths them, allowing the wrist pin to fit comfortably. Finally, the pistons sprayed by hot, deionized water, removing any lubricant or oil gathered through the manufacturing process. After they're dry, they're ready for use.

Piston Composition @ Process

• Aluminum - cast– Pour aluminum into a

mold– Light-weight– economical– Some silicone added– General usage– Brittle– Somewhat unpredictable

expansion qualities

Piston Composition @ Process

• Hypereutectic– Cast aluminum with

a high silicon content

– Light-weight– Higher performance– Less brittle– Predictable

expansion qualities

Notice the temperature difference between a forged piston and a cast piston.

Pistons are often cam-ground to produce the elliptical shape when the piston is at room temperature.