F91AC Piston Wrist Pin YSF9129 Replacement for YS Engine  [YSF9129]

Wrist pin for F91AC piston assembly

This component is supplied as a single wrist pin sized for the YS F91AC piston assembly. It provides the critical pivot between piston and connecting rod inside compact nitro engine cylinders and restores correct articulation when the factory pin is worn or damaged.

Piston movement and sealing are affected by wrist pin condition, so inspect the pin bore and piston skirt for wear, out-of-roundness, or looseness during maintenance. Replace the pin if you find scoring, deformation, or too much play to preserve alignment and dependable combustion performance.

Installation involves removing the engine top end to access the piston and rod. During reassembly, verify clip seating and clean contact surfaces, then run the engine gently to check that the piston moves freely and seals correctly under load.