79 ATC 110 piston size issue

[JDub14]

Rebuilding the engine out of my 79 Honda ATC 110 and the piston I pulled out of it has the 943 part# stamped on the side of it by wrist pin bore and “STD” is stamped on the piston dome. The issue I’m having is this piston mic’d out at 55mm and as far as I know, stock piston size in these were 52mm. Any help on this would be great. Plenty of 52mm replacement pistons, but very limited on 55mm.

[shortline10]

If it’s at 55mm then it’s a 123cc max big bore . The std on top obviously isn’t correct . Inside the piston if it was OEM would have ART as the manufacturer .