ive just recently bought myself another runner 172 arfter 2years of not owning one and it is the older shape engine with the clutch nut inside the case i have only ever had the rolling nut engines with the nut outside the casing, is there any diffrances in these two engines as i am going to be tuning the engine and dont want to just order and fit parts like i have my old bikes then relise when i go to put it on i needed a diffrant size or model ect.
There's differences in parts but not in any of the bits you buy when tuning. For example the rear pulley is different but if you were fitting an aftermarket clutch it would be the same. The gears are slightly different but if you were fitting a gear up it's the same for both types of engine. So basically you can fit whatever tuning parts to either engine and they will be the same.
just take your gearbox out first as there are 2 sorts or gears. there are splined and push on/press on gears.