I agree its time to bore it, here's a link to the kit from a reliable seller.
http://m.ebay.com/itm/MASTER-REBUILD...097?nav=SEARCH
Don't cheap out and buy the kit that doesn't come with the new connecting rod, I've seen to many Kohler's with broken rods to ever consider reusing one especially since there so cheap.
Since I'm not familiar with your engine building knowledge I will point out that before you order a kit you need to disassemble the engine and take it to the machine shop, they will measure the bore and the crank and tell you what size piston and connecting rod you need to order.