Found this 125cc race engine on e-bay... 300£ to start
BSA BANTAM 125 RACE ENGINE
CURIOSITY GOT THE BETTER OF ME SO I HAVE REMOVED THE HEAD AND BARREL
PISTON IS ON STANDARD BORE
ALLOY LINERED BARREL ALLOY CENTREPLUG HEAD
NEW PISTON
LOOKS TO BE UNRUN SINCE BUILD
ENGINE WILL BE SHIPPED STRIPPED
CARB AND STAND NOT INCLUDED
CUSTOM BARREL AND HEAD
EXACT SPEC UNKNOWN
PLEASE EMAIL ME FOR MORE INFO