Harley-Davidson Rear Cylinder Assembly M8 4.310 Bore Black Granite Touring TrikeHarley Davidson Rear Cylinder Assembly M8 4. 310 Bore Black Granite Touring Trike Increase the displacement of your Milwaukee Eight engine without removing the engine from the chassis. The Screamin Eagle team has engineered a patent protected 4. 310 Big Bore Cylinder that increases the internal bore but slips into the existing case bore without modification. When combined with the appropriate piston and flywheel combination in the Screamin Eagle Stage