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Jeep Cherokee
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Engine » 2.5L engine » Service procedures
Piston-fitting

BORE GAUGE METHOD

(1) 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.

Fig. 17 Valve Spring Tester
Fig. 17 Valve Spring Tester

1 - TORQUE WRENCH
2 - VALVE SPRING TESTER

(2) Measure the inside diameter of the cylinder bore at a point 49.5 mm (1-15/16 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 (Fig. 19).

(3) The coated pistons will be serviced with the piston pin and connecting rod pre-assembled. 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.

(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 (Fig. 18). 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.

(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.

Fig. 18 Moly Coated Piston
Fig. 18 Moly Coated Piston

1 - MOLY COATED
2 - MOLY COATED

Fig. 19 Bore Gauge
Fig. 19 Bore Gauge

1 - FRONT
2 - BORE GAUGE
3 - CYLINDER BORE
4 - 49.5 MM (1-15/16 in)

PISTON SIZE CHART

PISTON SIZE CHART

    More about «Service procedures»:

    Valve timing

    Valve, guide and seal

    Piston-fitting

    Piston ring-fitting

    Connecting rod bearings-fitting

    Fitting crankshaft main bearings

    Form-in-place gaskets

    Engine performance

    Honing cylinder bores

    Repair damaged or worn threads

    Service engine assembly (short block)

    Hydrostatic lock

    Engine oil service

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