Thanks Mckutzy and ML-Toys. Mckutzy, I agree grinding it myself may mess it up completely. I'm hoping there is a stock size that fits that engine.
MLToys, i've attached a couple pics.
The engine is a:
Robin Subauru 6.5 hp
prod. no. ex170d500105467
Air-Cooled, 4-Cycle, Slant Single-Cylinder...