Yamaha Oil Pump Outer YA2-28639-02-03. Overview. The Yamaha Oil Pump Outer YA2-28639-02-03 is a genuine original equipment manufacturer component designed to support the proper function of your engine's oil pump system. This outer housing plays a key role in maintaining consistent oil flow, helping to lubricate internal engine components and reduce wear during operation.. Proper lubrication is essential for engine longevity and performance. Over time, oil pump components can wear due to heat, pr