I picked this tool up for nothing with a few other misc items because it looked interesting and was going to be discarded. I've asked friends and mechanics and so far no one has any idea. It has no markings at all.

Piston ring groove cleaner???

Hey, you're right! I searched the term on ebay and found the exact tool listed. I had no idea. Thank you.

Wow I had no idea

Old mechanic here,  got a box of old, obsolete, not used anymore engine rebuilding tools,  got a twin to this, and a couple of more that do the same job.  Used a couple of them last summer on an antique tractor,  made feel a little old, hard won untapped knowledge. 

Nice... that one has what looks to be a depth stop adjustment screw. Not seen that on the common "cheep" ones
Joe B