2008 Polaris ATV Sportsman 300 400 H.O. Service Manual, Page 57Get this manual
ENGINE (300) Piston Identification
Piston is identified by the marking ES30ANote the directional and identification marks when viewing the pistons from the topThe letters "IN" must always be toward the intake side of the enginePiston rings must be installed correctly to ensure engine performanceThe numbers or letters on all rings (except oil control rings) must be positioned upwardSee text for oil control ring upper rail installationUse the information below to identify pistons and ringsEngine Model NoES300PFE012
Accessible Components
The following components can be serviced or removed with the engine installed in the frame: Flywheel AlternatorStator Starter MotorStarter Drive Oil pump Rocker ArmsRocker Shaft Camshaft
Oversize Standard Piston Available (mm) Identification