Piston Selection

NOTE: The cylinder bore must be within the specifications for taper and out-of-round before fitting a piston.

Select a piston size based on the cylinder bore.

Fig 1: Identifying Cylinder Bore Measuring Directions
Courtesy of FORD MOTOR CO.

NOTE: For precision fit, new pistons are divided into 3 categories (grade sizes). A paint spot on the new pistons indicates the grade size. Choose the piston with the correct paint color after measuring the cylinder bore diameter.

Fig 2: Identifying Piston Grade Size

Courtesy of FORD MOTOR CO.

Choose the piston with the correct paint color.
- Refer to ENGINE - 3.9L AND 4.2L article for the procedure.