Piston and Pin

Important:  Replace the pistons and the pins that are damaged or show signs of excessive wear.

The piston and the pin are a matched set. If service is required, replace the piston and the pin as an assembly.

Do not wire brush any part of the piston.

1. Clean the varnish from the piston and the pin with cleaning solvent.
2. Dry the piston and the pin with compressed air.
   Fig 1: Cleaning Varnish From Piston & Pin With Cleaning Solvent

   Courtesy of GENERAL MOTORS CORP.
3. Clean the piston ring grooves with a suitable ring groove cleaning tool.
4. Clean the oil lubrication holes and slots.
   Fig 2: Cleaning Piston Ring Grooves With A Suitable Ring Groove Cleaning Tool

   Courtesy of GENERAL MOTORS CORP.
5. Inspect the piston and the pin for the following:
   • Cracks in the piston ring lands, the piston skirt, or the pin bosses
   • Piston ring grooves for nicks, burrs, or warpage which may cause the piston ring to bind

     MINOR imperfections may be removed from the piston with a fine file.

   • Scuffed or damaged skirts (2)
   • Eroded areas at the top of the piston (1)
   • Scoring to the piston pin bore (3) or the piston pin
   Fig 3: Inspecting Piston & Pin For Damage

   Courtesy of GENERAL MOTORS CORP.
6. For certain 6.0 L applications, inspect for bent pin retaining clips or damage to the clip groove of the piston.
   Fig 4: Inspecting Pin Retaining Clips For Damage

   Courtesy of GENERAL MOTORS CORP.

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

7. Measure the piston ring-to-piston ring groove side clearance.
   1. 7.1. Insert the edge of the piston ring into the piston ring groove.
   2. 7.2. Roll the piston ring completely around the piston.
      • If binding is caused by a distorted piston ring groove, MINOR ring groove imperfections may be removed with a fine file.
      • If binding is caused by a distorted piston ring, replace the piston ring.
   Fig 5: Measuring Piston Ring-To-Piston Ring Groove Side Clearance

   Courtesy of GENERAL MOTORS CORP.
8. Measure the piston ring side clearance with a feeler gage.
9. If side clearance is not within specifications, try another piston ring set.Engine Mechanical (4.8L, 5.3L, And 6.0L) Specifications (LR4 VIN V)  or Engine Mechanical (4.8L, 5.3L, And 6.0L) Specifications (LM7 VIN T)  or Engine Mechanical (4.8L, 5.3L, And 6.0L) Specifications (L59 VIN Z)  or Engine Mechanical (4.8L, 5.3L, And 6.0L) Specifications (LQ4 VIN U)  or Engine Mechanical (4.8L, 5.3L, And 6.0L) Specifications (LQ9 VIN N)  .
10. If proper piston ring-to-piston ring groove side clearance cannot be achieved, replace the piston and pin assembly.
    Fig 6: Measuring Piston Ring Side Clearance With A Feeler Gage

    Courtesy of GENERAL MOTORS CORP.
11. To determine piston pin-to-bore clearance, use a micrometer and measure the piston pin.
    Fig 7: Determining Piston Pin-To-Bore Clearance Use A Micrometer & Measure Piston Pin

    Courtesy of GENERAL MOTORS CORP.
12. To determine piston pin-to-bore clearance, use an inside micrometer and measure the piston pin bore.

    Important:  The piston and pin are a matched set. If the clearance is not within specifications, replace the piston and pin as an assembly.

13. To determine the proper piston pin-to-bore clearance, subtract the piston pin diameter from the piston pin bore diameter. Refer to Engine Mechanical (4.8L, 5.3L, And 6.0L) Specifications (LR4 VIN V)  or Engine Mechanical (4.8L, 5.3L, And 6.0L) Specifications (LM7 VIN T)  or Engine Mechanical (4.8L, 5.3L, And 6.0L) Specifications (L59 VIN Z)  or Engine Mechanical (4.8L, 5.3L, And 6.0L) Specifications (LQ4 VIN U)  or Engine Mechanical Specifications (LQ9 VIN N) .
    Fig 8: Determining Piston Pin-To-Bore Clearance Use An Inside Micrometer & Measure Piston Pin Bore

    Courtesy of GENERAL MOTORS CORP.