F91AC Rocker Arm Screw YSF9135 by YS Engine  [YSF9135]

The YS Engine YSF9135 rocker arm screw is supplied as a replacement part for the F91AC engine series. It is intended to secure the rocker arm assembly during normal maintenance and modest tuning procedures on small model engines.

Designed for F91AC-pattern engines where the original item is specified. Prior to installation, check thread size and engagement depth to avoid interference with valve movement. Its role is mechanical: fastening the rocker assembly and preserving valve motion geometry through adjustments.

Fitting advice: remove the valve cover and rocker components as needed, line up parts carefully, and tighten to the engine maker's recommended torque. When altering rocker position for tuning, proceed in small steps and reconfirm clearances after each change.