Turbo Piston

Piston on Milling Machine

A piston from a turbo charged engine came into the machine shop that needed the compression ratio lowered. The customer could no longer find pistons that were dished with a lower compression ratio. The turbo pistons brought in needed to be dished 10 CC’s.
The first step was to do the math to find out how much material Tom should remove from the piston using a radius end mill and rotary table. Tom knew he would want to take out about 3 inches in diameter from the metal piston. He then converted 3 inches into centimeters. Then he did the reverse of “Pie R Squared” equals the area. Then he was left with the diameter. The end result was fifty thousandths that would need to be removed from the center of the turbo piston.
After milling out the center, Tom wanted to double check the results.
Tom used a CC Kit to measure the milled out space. A CC Kit includes a small piece of plexiglass, with a tiny hole in it, and a measuring beaker.
The first step is to seal the piston with grease and set the plexiglass on top. Next, fill the beaker to the top measuring line. Then carefully release water into the area that has been milled while holding plexiglass in place.
The beaker measurements told Tom how much volume was milled out of the piston dish.
A CC Kit can be used on pistons and heads to establish an accurate measurement.