When was z155 first produced?

[Will_505]

Hi all, random question coming. I've got a z155 engine in atm which I'm rebuilding but it's the older model I know this because it's got the 13mm kickstart shaft rather than the 16mm on the 2 new generation engines so this must be the first model Z155 engine. My question being when were they first made? Like when was the first generation first sold?
Cheers 👍