In 1998 when Yamaha changed the 125 engine to a 54x54 non-powervalve type, piston clearance went from 0.045-0.055mm on the old 56x50 model to 0.075-0.085mm on the new one.
I understand the increased clearances were to allow for lower octane unleaded fuel, and possibly due to the bridged exhaust.
I still have access to good quality leaded race fuel and was wondering what others in a similar situation were using for piston clearances. 0.075mm seems a bit sloppy... I'm interested in hearing from others still running the newer type 125.
I think there was also a change in piston manufacturing. And as the leaded piston era pistons ran out, the manufacturing that replaced it was different and required the extra clearance regardless of whether leaded or unleaded fuel was used.
Bookmarks