Figure 3-13. Controlling Piston Expansion.
across the larger diameter to keep from rocking.
(1) Lightens the piston, which, in turn,
As it warms up, it will expand across its smaller
increases the speed range of the engine.
diameter at a much higher rate than at its larger
diameter. This will tend to make the piston round
(2) Reduces the contact area with the
at operating temperature. Virtually all pistons in
cylinder wall, which reduces friction.
automotive applications are cam ground.
(3) Allows the piston to be brought down
f. Partial-Skirted (Slipper-Skirt) Pistons
closer to the crankshaft without interference with
(Fig. 3-15). The purpose of the piston skirt is to
keep the piston from rocking in the cylinder. The
g. Strength and-Structure (Fig. 3-16). When
slipper-skirt piston has large portions of its skirt
designing a piston, weight and strength are both
removed in the non thrust areas. Removal of the
skirt in these areas serves the following
Figure 3-14. Cam-Ground Piston.