A piston ring that has a nickel-iron or comparable metal insert cast into the piston heads. The top ring groove is cut into this metal. As the top ring grooves in aluminum pistons pound out of shape, this insert groove will prolong the useful life of the piston and ring.
TOP RING GROOVE INSERT
Meaning of TOP RING GROOVE INSERT in English
English dictionary of automotive terms. Английский словарь автомобильных терминов. 2012