91SR Back Plate O-Ring Replacement YSS9117 by YS Engine  [YSS9117]

The YS Engine YSS9117 O-ring is produced as a service part to interface cleanly with 91SR back plate assemblies. Its purpose is to form a reliable seal at the junction of the back plate and engine housing to reduce leakage during operation and inspection.

Fit and compatibility: this O-ring corresponds to the back plate interface used across 91SR engines and provides a straightforward sealing solution without changing back plate geometry. Always inspect mating surfaces for damage before attempting fitment.

Installation notes: carefully extract the worn seal to prevent scoring the bore, clean the surfaces, and lay the O-ring evenly into its groove. Using a light, compatible lubricant can assist fitting and prevent the ring from twisting. Perform a static leak assessment after assembly.

Service impact: while not intended as a performance upgrade, the O-ring helps maintain consistent engine behavior by ensuring the back plate seal remains intact. Replace it if you detect degradation or seepage during maintenance.