<P> Most automotive pistons have three rings : The top two , while also controlling oil , are primarily for compression sealing ( compression rings ) . Meanwhile , the lower ring is for controlling the supply of oil to the liner , which lubricates the piston skirt and the compression rings ( oil control rings ) . At least two piston rings are found on most piston and cylinder combinations . Typical compression ring designs will have an essentially rectangular cross section or a keystone ( right angled trapezoidal ) cross section . The periphery will then have either a barrel profile ( for the top compression rings ) or a taper napier form ( for the second compression ring or scraper ring ) . There are some taper - faced top rings as well , and on some old engines simple plain - faced rings were used . </P>
<P> Most automotive pistons have three rings : The top two , while also controlling oil , are primarily for compression sealing ( compression rings ) . Meanwhile , the lower ring is for controlling the supply of oil to the liner , which lubricates the piston skirt and the compression rings ( oil control rings ) . At least two piston rings are found on most piston and cylinder combinations . Typical compression ring designs will have an essentially rectangular cross section or a keystone ( right angled trapezoidal ) cross section . The periphery will then have either a barrel profile ( for the top compression rings ) or a taper napier form ( for the second compression ring or scraper ring ) . There are some taper - faced top rings as well , and on some old engines simple plain - faced rings were used . </P>
the minimum number of rings in a piston is
the minimum number of rings in a piston is
two
two