xtr 250 gearbox trouble

Hi peeps my name is Gus from australia. I bought an xtr 250 with the air cooled ohc engine and I'm blowing up gearboxes like crazy. I'm about to put in my 3rd gearbox and 'm not even due to change my first piston rings. These engines are found in the galaxy xtr 250 and the pitster pro xtr 230. The gear I use the most is 3rd and it's the one that ends up with no teeth left so I figure these gearboxes are made poorly. Does anyone know of a japanese made gearbox that is compatible with my engine? It's a cb250. Any help will be greatly appreciated.

Gus.

Is this the one that keeps breaking?

http://www.contactdi.com/2012/enduro/IMG0778.jpg

Had the same thing happen to me. Have you been replacing all the gears or just #3?

The engine is a copy of the Honda FTR223, but I don't know if the gear box is exactly the same.

Cheers!
ChinaV

Thanks for the reply man. I think that's the one, I'd have to go out in my garage for a look. Both the gears for 3rd are chewing out on mine. I can't get only 3rd gear unfortunately. I have to get the whole gearbox from the guy I get my stuff from. It gets sent from china so I have to wait a little while for it. If I can't get another type of box that's stronger I' going to make sure I've got a backup one all the time. It only lasted me about 7 hours tops. I don't think they are hardened like the japanese ones are. Will have a look at your suggestion. Also, I've seen a gearbox made by loncin for these engines that has some different combos of gearing than the gearbox I have now. Just need to get the digital calipers out to check some diameters, lengths etc. May last a little longer but doubt if it is hardened again. What bike do you have? Is it only 3rd that's gone on yours? Just had a look at the ftr and it looks the same hey. Thanks man, Gus.