MZ/MuZ Riders

What is the largest capicity that can be built on to a TS125 engine ...i know 150cc is easy but what is the largest capicity that can be built using other pistons etc ...and retaining 5k reliable mileage ??? Burwins .. ..? ? over to you... the small crank journels are always going to be a problem..i believe ..??

BSA pushed their copy of this engine up to 175cc in the 1960s as the Bantam. I belive they had to redesign the cylinder though. Not sure if they also increased the stroke. Would it be possible to fit a 175 topend (cylinder, piston and head)?