just purchased a thundercat motor for a project, 2nd is goosed apparently common fault, does anybody know if the 3tj gears are compatable, before i strip it ?

dunno, but ive got a couple of sets of 3en1 gears if you need any to try!

hiya, I don't think there compatible, different part numbers I believe.

I have fixed two gearboxes so far by replacing the box with second hand ebay sourced units, not the easiest of jobs and if I have to do it again I would use oem new parts. The second hand ones, no matter what people tell you about there condition always come with wear marks/burrs on the second gear dogs!

Check out this article;

http://orbitalair.wikispaces.com/file/v ... x_RevB.pdf

I have also been considering trying to get hold of one of the factory pro shift kits for my own bike as its supposed to help, giving a more positive shift.

The main problem though, is that first gear is too low (in relation to second) and if you try and rush through to second the engine revs don't drop quick enough. The input shaft ends up spinning too fast for it to accept second,causing it to 'bounce out' and wreak the dogs and bend/wear the selector fork.

I think you could probably get them to fit - the cases are common afterall. I'm not sure they'd be that useful though.
I'd imagine the 400 ratios would be lower overall, the top speed is lower on the 400, you could control that through the sproket ratio though. If you were to do this you might end up juggling the sprokets which could cost more in the long run. Be interesting though.

Gearbox change on the YZF motors is easy as they are a cassette type. The YZF750 box fits (if you can get one)

didnt know the yzf 750 box was the same, played about with them a fair bit & built a few, still got a yzf now for trackdays, to trick to strip that tho ! i will keep you informed once it is striped and out of the t-cat,

They're not cassete type, you need to split the cases .... a cassete box you don't.

i know evil, think he means they look the same box, they do look the same but i will have to have a look when it is stripped, as i have a yzf750 kit gearbox,if it fits iam sorted ! as any body got part numbers for the 600 g-box,so i can check ?

I've seen a few boxes too

750 g-box will not fit, stripped the gear box down, so i will replace with new gears, just out of interest, the oil ways on the 600 are the same as the 400 so oil way mod will be done as well as it will spend its life on the track