It is common practice, once the piston is set into the cylinder with the ring compressor installed to tap on the top of the compressor to "square it up". Usual procedure is to then use the hammer handle and tap the piston home. The sketch below depicts this and points to areas of damage.

The inside area of the band becomes rolled over, nicked, etc. and causes damage to the rings when they are installed.

It is recommended after the piston is set into the cylinder the piston be gently tapped with hammer handle to square up the piston. The piston can then be tapped or pushed into position in the cylinder.

It is also recommended that the inside lower edge of the installing band be checked frequently for nicks, dents and other damage by running a thumb and forefinger completely around the band.

This practice will insure a better performing engine when the job is done.

(P90)