This manual provides comprehensive technical information for the Aprilia Rotax 123 Engine, a powerplant renowned for its performance and reliability in various Aprilia motorcycle models from the late 1980s through the 2000s. The Rotax 123, a two-stroke, single-cylinder engine typically displacing 123cc, is celebrated for its robust design and tuneability, forming the heart of many successful Aprilia sportbikes and off-road machines. Its engineering quality is evident in its performance characteristics, known for strong mid-range and top-end power delivery, often enhanced by features like Aprilia's Exhaust System (A.E.S.) power valves.

This Factory Service Manual / Repair Manual, presented in English, is designed to be the definitive technical resource for professional motorcycle technicians, mechanics, and experienced DIY enthusiasts. It covers all essential engine systems, including the cylinder head, block, piston, crankshaft, lubrication, cooling, fuel, and ignition systems, along with detailed disassembly and reassembly procedures. The manual offers professional technician-level depth, featuring precise specifications, tolerances, exploded views, and step-by-step repair instructions crucial for accurate diagnostics, efficient maintenance, and complex rebuilds, ensuring the longevity and optimal performance of the Rotax 123 engine.