Sifton Oil Pump Drive Gear Kit For Harley Knucklehead / Panhead 1939-1953 Sifton high flow pinion shaft oil pump drive gear for the 1939-53 OHV Big Twin comes with a 6 tooth gear increasing your oil flow rate by approximately 25. Features Requires use of late style oil pump similar to OEM 26345-73 Increases oil flow rate by approximately 25