1985-1986 Honda ATC250R Shop Manual, Page 16Get this manual
GENERAL INFORMATION
OPTIONAL PARTS LIST
ITEM REMARKS 0.25 mm, 0.50 mm (2 sizes) The cylinder must be rebored, and an oversize piston and piston rings fitted if worn or seizedUse the correct oversize piston rings with an oversize piston0.25 mm, 0.50 mm (2 sizes) NOTE: After reboring, remove all burrs from each port edge and chamfer as indicated belowCYLINDER
ENGINE Oversize pistons
Piston oversize 0.25 mm (0.01 in) 0.50mm (0.02 in) Cylinder I.Dmm (in) 66.270-66.285 (2.6090-2.6096) 66.520-55.535 (2.6189-2.6195) Cylinder I.DService limit mm (in) 66.320 (2.6110) 66.570 (2.6209)
Piston oversize 0.25 mm (0.01 in) 0.50 mm (0.02 in)
0.3 mm 10.01 ;nl
SIDE 1.2mm L