Hey everyone. Brand new here and picked up my first Bultaco. It runs and is about 75% original, however knowing this is a trial forum, I am looking to go the other way. I would like to change the gearing some to make it more of a "desert sled", less low-geared trials. I know the 71 Alpina is basically the same bike with higher gearing. Can anyone tell me how interchangeable the gearbox is?

Any input would be appreciated.

Thanks!
Fenix

If you’re looking for a “Desert Sled”, get yourself a Pursang or a Frontera.

The gearbox from an M85 Alpina should go straight in but later models will have differences in shaft diameter and clutch hub mounting so aren't a straight swap

Much easier to just change the sprockets than gearbox ratios. Standard Sherpa size for that year is 11 / 46 for a 520 chain or 13 / 52 for a 428 chain, just fit bigger front, smaller rear

Thanks for the response guys. Woody - I did get a larger front counter sprocket. I'll start there.

 

You don’t say what model of Bultaco you have. This is key. I have an M98 Alpina that I turned into a trials bike for vintage trials. I used the trans gears and heavier primary flywheel from an M91 Sherpa T to compliment all the other modifications.