Purpose of 5th ring

[cranetruck]

The LDS465-2 engine was designed for more power and higher goverened speed (rpm), one modification was the addition of a 5th piston ring, anybody have an educated opinion on its purpose?
Guess it would keep the piston better aligned...or is that not a problem?

 

[yorkgulch2]

It seems like that is the most likely reason. You see scuffing on the cylinder and lower piston skirt especially on stroked gas motors. A ring lower down on the piston would probably help alignment of the piston.

 

[rdixiemiller]

Piston alignment would be my guess. Many of the old industrial motors had lower guide rings.