Wrangler 4WD L4-150 2.5L VIN P MFI (1998)
Piston: Service and Repair
Fitting Pistons
BORE GAUGE METHOD
1. To correctly select the proper size piston, a cylinder bore gauge, capable of reading in 0.003 mm (0.0001 in.) INCREMENTS is required. If a
bore gauge is not available, do not use an inside micrometer.
Bore Gauge
2. Measure the inside diameter of the cylinder bore at a point 49.5 mm (1-15/16 in.) 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.
3. The coated pistons will be serviced with the piston pin and connecting rod preassembled. The coated piston connecting rod assembly can be
used to service previous built engines and MUST be replaced as complete sets. Tin coated pistons should not be used as replacements for
coated pistons.
Moly Coated Piston
4. 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. 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 (0.0001 in.) increments is required.
5. 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.
