Rocker Arm Fastener YSF9135 for F91AC - YS Engine  [YSF9135]

The YS Engine YSF9135 is a replacement screw intended for use in the rocker arm area of F91AC engines. It provides the mechanical fastening required for routine servicing and modest tuning on model powerplants.

Intended primarily for F91AC-design installations where the original item is specified. Verify thread diameter and engagement depth before reuse to avoid interference with moving valve components. The part secures the rocker assembly and helps keep valve motion geometry stable during adjustments.

Fitting steps: remove the valve cover and rocker assembly as necessary, ensure correct alignment then tighten following the engine manufacturer's torque guidance, and remeasure valve clearance. For tuning, small incremental changes to the rocker mount are recommended with clearance checks after each step.