Piston Fitting

To correctly select the proper size piston, a cylinder bore gauge, capable of reading in 0.003 mm (.0001 in.) INCREMENTS is required. If a bore gauge is not available, do not use an inside micrometer.

Measure the inside diameter of the cylinder bore at a point 38.0 mm (1.5 inches) below top of bore. Start perpendicular (across or at 90 degrees) to the axis of the crankshaft at point A and then take an additional bore reading 90 degrees to that at point B. See Fig 2.

Fig 1: Typical Moly Coated Piston

Courtesy of CHRYSLER LLC

1 - MOLY COATED

2 - MOLY COATED

Fig 2: Measuring Cylinder Diameter With Bore Gauge - Typical

Courtesy of CHRYSLER LLC

1 - FRONT

2 - BORE GAUGE

3 - CYLINDER BORE

4 - 38 MM (1.5 in)

The coated pistons will be serviced with the piston pin and connecting rod pre-assembled.
The coating material is applied to the piston after the final piston machining process. Measuring the outside diameter of a coated piston will not provide accurate results. See Fig 1. Therefore measuring the inside diameter of the cylinder bore with a dial Bore Gauge is MANDATORY . To correctly select the proper size piston, a cylinder bore gauge capable of reading in 0.003 mm (.0001 in.) increments is required.
Piston installation into the cylinder bore requires slightly more pressure than that required for non-coated pistons. The bonded coating on the piston will give the appearance of a line-to-line fit with the cylinder bore.