PE95K Military Generator Piston Rings

[onan]

Hello:
I am new to the forum and this is my first post. I collect and restore vintage military generators. (14). I an presently restoring a 70 year old PE95K that has suffered many years of bad storage. There were two cylinders seized with a lot of rust and carbon. On removing the pistons, I noticed that there are four ring groves and only three rings. The top groves were full of carbon. Is the top grove not to have a ring in it? All of the ring sets that I have seen have only had three rings In them. Can someone clue me in on what the story is on the missing ring. The engine is the four cylinder jeep engine.
Any info would be appreciated.
Thanks
Jerry

[Joe Gopan]

The top groove is what is called a "Heat Dam" and helps prevent carbon forming the top ring groove, the groove for the "Heat Dam" has no ring. There is a brand commercial replacement Jeep piston that do not have this "Heat Dam", the name of that brand is Badger.

[artificer]

www.hastingsmfg.com/ServiceTips/piston.htm

[onan]

Thank you all for the information. Makes sense to me.
Thanks
Jerry