Scheme of metal removal from a piston to adjust its mass
The arrows indicate the places where metal can be removed.
The mass of pistons in one engine must not differ from each other by more than ±2.5 g.
If there is no set of pistons of the same weight group, it is possible to remove some metal at the base of the piston pin bosses. However, the metal removal should not exceed 4.5 mm in depth relative to the nominal piston height (59.40 mm), and the width is limited to a diameter of 66.5 mm.
Information taken from the website: vazbook.ru