GEAR 9G5842 - Caterpillar

3400 Family Of Direct Injection (DI) Engines With 7N3509, 8N1606, 8N1607, 1W9372, 2W865 Or 7W3668 Piston Body AssembliesThere have been some reports of cracking at the piston crater rim on the above engines. This problem may occur under extreme engine operating conditions. The fuel system and engine application should be checked on engines with piston crater rim cracks to make sure they are operating at the correct specifications.
Previously, Caterpillar recommended not to reuse a DI piston with crater rim cracks that were visible without the use of magnification. See Guidelines For Reusable Parts, Form SEBF8049, Page 15. Recent engineering lab tests now indicate that piston reuse is allowable on certain 3400 DI pistons. The allowable rim cracks can be located in ZONE A only and can extend a maximum of 5.0 mm (.20") downward or outward from the inside crater rim edge. See the illustration.
This recommendation applies only to the 7N8509, 8N1606, 1W9372, 8N1607, 2W865 and 7W3668 Piston Body Assemblies used in the 3400 Family of Direct Injected Engines.
Allowable location and size of minor rim cracks.