YS Engine YSS9117 Back Plate O-Ring, back plate seal for 91SR series  [YSS9117]

This YS Engine back plate O-ring is an RC-scale replacement seal designed to interface with 91SR-series back plate assemblies. It serves as a dedicated sealing element to limit fuel and oil leakage where the back plate meets the engine housing, preserving proper operation during routine use and inspection.

Fit and compatibility: the part matches the back plate interface used on 91SR engines, providing a direct sealing solution without modifying the back plate geometry. The O-ring's role is purely mechanical sealing, so confirm the mating surface is clean and free of damage before installation to ensure a proper seal.

Installation notes: remove the old seal carefully to avoid nicking the back plate bore, clean mating surfaces, and seat the O-ring evenly in its groove. Light, compatible lubricant can ease installation and help the O-ring seat without twisting. After assembly, perform a static leak check before returning the model to regular use.

Tuning and maintenance role: while this is not a tuning item, a serviceable O-ring contributes to consistent engine behavior by maintaining correct sealing under normal operating conditions. Replace as part of routine engine servicing when you observe wear, flattening, or any loss of sealing performance.