R 21RX/21XM Crankshaft Ball Bearing OS23930000 for O.S. Engine  [OS23930000]

Support bearing for crank rotation and balance

The replacement crankshaft ball bearing is intended for RC model engines identified as O.S. Engine R 21RX and 21XM in the product listing. Its role is to support the crank during rotation, reduce frictional losses, and help preserve shaft alignment under load.

Fitting guidance: remove contaminants from the crankcase seat and inspect for damage prior to pressing the bearing in, use an appropriate press or driver that seats the outer race evenly, and confirm smooth free rotation and correct axial clearance after installation. If you notice any roughness, play, or overheating, replace the bearing promptly.

A practical replacement component for restoring correct bearing fit and crank alignment during servicing or rebuilds to help maintain engine reliability and response.