40SF Series Piston Pin Precision Replacement - OS25406000 by O.S. Engine  [OS25406000]

Wrist pin replacement for 40SF engines

The O.S. Engine OS25406000 piston pin replaces the internal wrist pin in 40SF series RC glow engines, securing the piston to the connecting assembly and correcting piston-to-rod play. It is intended to restore original internal clearance where wear has compromised fit.

Before final assembly confirm orientation and fit, fully seat retaining clips or circlips in their grooves, and check piston travel inside the sleeve to ensure smooth operation. The pin is an internal component that preserves piston alignment and repeatable compression, which helps support steady idle and throttle response during tuning.

When servicing a 40SF engine inspect the piston skirt, wrist pin bore, and retaining clip seats for scoring or deformation; replace any worn components as a matched set to preserve factory running tolerances. Regular inspection aids in keeping needle settings and carburetion consistent between tune-ups.