Piston Selection (Unit Repair)

IMPORTANT:  Measurements of all components should be taken with the components at normal room temperature.

For proper piston fit, the engine block cylinder bores must not have excessive wear or taper.

A used piston and pin set may be reinstalled if, after cleaning and inspection, they are within specifications.

1. Inspect the engine block cylinder bore. Refer to ENGINE BLOCK CLEAN AND INSPECT .
2. Inspect the piston and the piston pin. Refer PISTON, CONNECTING ROD AND BEARINGS CLEAN AND INSPECT (UNIT REPAIR) .
   Fig 1: Inspecting Engine Block Cylinder Bores For Excessive Wear Or Taper

   Courtesy of GENERAL MOTORS CORP.
3. Use a bore gauge and measure the cylinder bore diameter. Measure at a point 64 mm (2.5 in.) from the top of the cylinder bore.
4. Measure the bore gauge with a micrometer and record the reading.
   Fig 2: Measuring The Cylinder Bore Diameter

   Courtesy of GENERAL MOTORS CORP.
5. With a micrometer or caliper at a right angle to the piston, measure the piston 14 mm (0.570 in.) from the bottom of the skirt.
6. Subtract piston diameter from the cylinder bore diameter in order to determine piston-to-bore clearance.
7. Proper piston-to-bore clearance is 0.010 - 0.041 mm (0.0006 - 0.0016 in).
   • If proper clearance cannot be obtained, select another piston and measure clearances.
   • If proper fit cannot be obtained, hone the cylinder bore or replace the cylinder block.
8. When the piston-to-cylinder bore clearance is within specifications, mark the top of the piston using a permanent marker for installation to the proper cylinder.
   Fig 3: Measuring Piston Head Diameter

   Courtesy of GENERAL MOTORS CORP.