This service manual covers the KTM 400 660 LC4 Engine, with production years spanning from 1998 through 2005. Designed for demanding off-road and dual-sport applications, the LC4 engine is renowned for its robust construction and reliable performance. Its engineering emphasizes durability and power delivery, making it a favored choice for riders who require a dependable powerplant for adventurous journeys and competitive use. This manual provides comprehensive information to ensure the continued optimal operation of your KTM engine.

The purpose of this manual is to serve as a definitive guide for the maintenance, repair, and technical understanding of the KTM 400 660 LC4 Engine. It details essential procedures, diagnostic techniques, and specifications necessary for owners, technicians, and mechanics. Coverage includes routine maintenance schedules, detailed disassembly and reassembly instructions, troubleshooting common issues, and essential technical data. By following the guidelines within this manual, users can effectively maintain their engine's performance, longevity, and safety.