Sachs 50cc racebike. I havenīt had a Sachs engine in my hands since my motocross- days in the seventies. Back then the Italian built Simonini had a 6speed engine, which now is known as the longstroke version. The early version having a bore and stroke of 38/44mm were replaced by a new engine in 77, a shortstroke with 40/39,7mm dimensions. The new version retained its outer dimensions, transmission and clutch layout.