DT/YZ gearbox

[cloggy]

Can anyone tell me for how many years/models Yamaha used the original DT box? I know the ratios will be different but we need a gearbox to fit in a Champion framed DT1/2 engine case. Eventually the bike starting jumping out of second gear and upon splitting the whole gearbox isn't good.

[sleepy]

Not 100% sure but all the later DT1's through to DT3 and RT1 - RT3 had the same gearbox but the DT250-360 are different but some gears interchange. The DT1 MX had close ratio version of the same box and probably the DT2MX had the close ratio box but these would be near impossible to find. The YZ250-360 A and B shared the same crankcase as the DT so would probably fit and I've been told some of the MX250 gears will fit on the shafts but not the entire box. The early DT1's up to late 1969 had a different selector and may not fit the later cases.
Hopefully the is a Yamaha tragic out there with more knowledge than me but I would think you have more chance of getting a used DT1-3, RT1-3 box than any of the YZ or MX models as there was a lot more sold but then a lot more have gone to land fill.   

[crossedup2]

I'm running an MX250a gear set in a RT3 bottom end. From memory you run the DT / RT selector forks. Pretty sure as stated the early DT cases were a little different.

It could be as simple as sliding the gears you want on to the original shafts. Also worth noting is that I think its 4th gear ratio is same on the DT/RT and the MX250A. From memory you have to use the DT output shaft. MX360A have the balance chain driver but it you track down a MX360 gear set you can still use original DT shaft with 1st gear from DT gear box. You don't need it after your moving anyway.

Set of verniers and a bit of space to set the two gear sets down will make all the difference.
Good luck.
Peter B