GM 6.5L V8 – Piston Features

Each piston is made of cast aluminum and has the following features (refer to Figure 2-14):
• A face with a special combustion chamber indentation
• A cast-in insert for a top compression ring with a keystone-shaped cross section
• A machined groove for a 2nd compression ring
• A machined groove for a two-piece oil control ring
• Bores for a full-floating piston pin, secured at each end by a round wire retaining ring
• A machined outer diameter with a specially shaped skirt area

During service, several critical piston installation procedures are followed:
• Each piston ring is checked for correct end gap clearance before it is installed.
• Each piston ring groove is cleaned without removing metal.
• The compression rings are installed with identification markings facing upward.
• Installed piston rings are checked for free movement in their grooves.
• Each piston ring gap must be aligned (refer to Figure 2-15).
• Before installation into the cylinder bore, the piston and rings should be coated with engine oil.
• During installation, the combustion area on the face of the piston must face toward the outside of the cylinder case.

Installation of each piston pin retaining ring requires the use of special tool J 29134-A. After installation, each ring is checked for proper installation in its groove. The opening in a retaining ring that has been installed should face downward (toward the crankshaft).

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