I have one of those Kazuma / Redcat SFX-110 ATV. It moves forward perfectly, but when you put it in reverse, it grinds and doesn't move at all.
I opened up the case on the right with the clutch. Everything looks really clean. no broken parts.
I think it is the Counter Gear Assembly Transmission under the clutch:
Counter Gear Assembly for Chinese 110cc ATV Transmission - $39.95 - Redcat ATV Parts Online

I don't want to dismantle the wrong side. Does anyone have any help?

I am turning this into an incredible art project over the next two weeks and really need to get it going!

 

Welcome to the forum SFRedcatMPX110!

Those are the gears Id look at too...The engine will need to be removed and the cases split to access those gears..