O.S. Engine OS25406000 Piston Pin for 40SF Series  [OS25406000]

Piston pin for 40SF engines

The O.S. Engine OS25406000 piston pin is a direct replacement part intended for use with 40SF series RC glow engines, serving as the internal wrist pin that secures the piston to the connecting assembly. This is an RC-scale accessory designed to restore correct internal fit where the piston-to-rod interface shows wear or play.

Installers should confirm fit and orientation before final assembly, ensure retaining clips or circlips seat fully in their grooves, and verify smooth piston movement within the sleeve after installation. The pin's role is purely internal: it maintains piston alignment and repeatable compression characteristics that affect idle stability and throttle response during tuning.

When servicing a 40SF engine, inspect the piston, wrist pin bore, and retaining clip seats for scoring or deformation and replace any worn components as a set to preserve original running tolerances. Regular inspection helps keep needle settings and carburetion behavior consistent during tuning sessions.