The International Cessna^® 170 Association

Bought a Atlas TH42 lathe today. In the box of stuff I can not identify was this tool. It is not a Atlas part for the lathe but might be used on a lathe. It has the mark AC as in AC spark plugs molded into it and the words PAT PENDING with no numbers. On the top of the crank handle it has a direction arrow and says To Close Gap. It has what is left of a dark navy blue crinkle finish.

The lathe was owned by a gentleman who flew in WW2. He was associated, lived near or worked at a large airplane manufacturing plant and amassed a collection of aircraft related tools over his life that has been described as a massive collection of any tool you can think of. So while this could be a tool for the lathe I'm thinking it is some kind of aviation related tool made by AC that happened to fall into the lathe tolling box.

Has anyone ever seen one and know what it is?

Looks similar to the spark plug gapper that I borrow every annual.

On the one I use, the plug comes up, from below and is held/adjusted by an adjustable bushing (utilizing shims to adjust the gap as required for the plug type being set) then the little pointer is flipped down against the electrode and a lever is rotated which bends the electrode precisely time after time.

It's a spark plug gap adjusting tool.

Cool thanks Jim and BL. After I saw the AC and the word gap I thought maybe it was but the hole is to big to hold the plugs I have (REM40). I guess there are different size hole or maybe adapters that go into it. Sure seems a complicated tool compared to this:
I'll keep it and put it in my tool collection and never use it and my kids will wonder what the heck it is when they're getting rid of my pile of toys when I'm gone

Hey! I been WONDERIN' where my AC Spark Plug gapper went! I forgot I'd loaned it out to some machinist up nawth.
I'll pay the freight, Bruce.... go ahead and send it to me C.O.D.

Well I'll at least have to bring it to convention so you can visit with it and show me how to use it after I get it back home.

I have a similar one that works like this: The lever is held in place by an unthreaded bolt inserted from the other side. Pressing the lever moves a shaft attached to the fixed spindle wheel, which by resisting movement transfers the force to the press pin. When the pin hits its stop (machined into a boss in the base casting) the lower arm rotates, pulling the guide wire up until the tension equals the preset tension on the adjustment screw spring. This causes the overcenter cam to pivot, allowing the magnetic actuator to close against the circular plate. Now the push pin moves very slowly, at a rate set by the balance of forces between the friction thumbscrew and upper reverse counterweight (which is temperature compensated), against the spark plug electrode, setting the gap. Works every time!

That's a joke. Actually, I have fine-wires.