Usage:
- SUPPLEMENT: 06/01/87
SERVICE MAGAZINE, DECEMBER 1, 1986, PAGE 10, "Use Correct Pistons And Rings For 340B Truck Engines". Put a mark through this article and make reference to the article with the same title in this issue.
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Three different pistons are used in 3406B Truck Engines. The piston used will depend on many factors, including horsepower rating, engine arrangement and engine application. Chart A gives some of the uses and design features of the different pistons and includes the 7C490 Basic Piston Group used in CARB (California Air Research Board)/ATAAC (air-to-air aftercooled) engines.
The 7C490 Basic Piston Group is used in the 400 horsepower arrangement of 3406B CARB/ATAAC Truck Engines. CARB truck engines are designed to meet the stricter emission standards required for trucks operating in the state of California. They deliver rated horsepower, with high efficiency, while meeting lower emission level requirements. In order to meet all of these requirements, without decreasing service life, special pistons are used in the 400 horsepower arrangement of 3406B CARB/ATAAC Truck Engines. A high ring position and a tight top land (reduced clearance between piston and cylinder liner) are combined to reduce the dead air volume in the cylinder and provide increased combustion efficiency. A plasma coated top ring is used for necessary scuff and wear resistance. An "offset" wrist pin bore helps control piston slap in the cylinder liner.
NOTE: "Offset" pistons have the word FRONT marked on the top of the piston for installation purposes.
Pistons designed with tight top lands are susceptible to cylinder liner polishing (and premature loss of oil control) from carbon build-up on piston surfaces. It is important to strictly observe all oil change and scheduled maintenance intervals given in the Operation and Maintenance Guide.
NOTE: "Cylinder kits" should not be used for in-frame engine overhaul on 300 hp CARB/JWAC 3406B Truck Engines 7FB27302-Up, or 400 hp CARB/ATAAC 3406B Truck Engines 7FB45983-Up. Use cylinder kits to service only those engines equipped with 1W9373 Piston Groups.
Chart B gives parts service replacement information for the piston groups used in 3406B Truck Engines.
