A percentage of Model “A” cars are now being equipped with solid skirt pistons. These pistons are a trifle lighter than the slotted skirt design and consequently should not be used interchangeably.
The piston heads in the solid skirt pistons are fitted with a non-expanding steel insert anchored to the center of the piston head.
This steel insert projects through the second ring groove and bears against the piston ring which in turn rides against the cylinder wall. The insert and ring are snugly fitted to the cylinder and hold the piston in a centralized position.
The skirt of the piston is machined to an oval cone with its largest diameter across the piston pin and in line with the connecting rod wall thrust.
With the piston cold the lower end of the skirt fits snugly across the pin with ample clearance in front and rear. This gives the piston approximately zero clearance in line with the connecting rod thrust and ample clearance in the cylinder at the front and rear of piston to allow for necessary expansion.
Before assembling the connecting rods to the pistons, each rod must be accurately aligned on the connecting rod aligning jig.
Due to the design of the solid skirt piston, it is unnecessary to check the assembly for alignment after the piston is assembled to the connecting rod.
Feelers are not used when fitting the solid skirt pistons in the cylinders. The pistons, however, must be a snug fit at both top and bottom across the cylinder.
Note that insert in head of piston projects through center ring groove and bears against piston ring. Also that skirt of piston is machined to an oval cone with the large diameter across piston pin and in line with connecting rod wall thrust
This view shows opposite taper on piston. Note that the reverse taper gives maximum clearance at bottom of skirt. This feature permits full free expansion of the piston