I have a 46 SF in a box marked ABC but the engine looks like it has a ring, when viewed through the exhaust. There are no instructions. How can I be sure if it's ringed or ABC/N since the break-in for the engines are very different. Thanks Dave

O.S. made the .46 SF engines is both ringed and non-ringed. The non-ringed engines had the nickel-plated liners. With a good fuel that contains castor oil, there should be no issues.

As far as whether it has a ring or not, you can just look into the exhaust port to see. The ring will be a dark-colored band about 3/32" below the top of the piston. The non-ringed engine will have just a small groove a bit below the top of the piston, but the side of the piston will be all aluminum colored.

You can also tell if you remove the cylinder head. The ringed engine had a steel liner. A magnet will easily help you tell the difference.

An easier way to tell, in my experience, ABC sleeves have OPEN exhaust port, vs Ringed Engines have an exhaust port with a "Divider" portion bridging the opening. Someone else chime in on my findings.