Crankcase On Triumph Street Scrambler 2018

I would be surprised if it would fit, the 2012 Bonneville is an air-cooled model and your street scrambler is water cooled. I understood that the engine was completely redesigned for the water-cooled models

 

Looking at the two crank cases on Fowler’s parts site, based on those part numbers they look very different.

 

Just another thought, before buying one half of the crankcase, make sure that they are not fitted as a matched pair. I was under the impression that the cases are line bored as a matched pair.