Piston Rings

[Lonnie Grissom]

My all about small engines book states that rings were a simple split ring made of cast iorn. The book shows two examples a concentric piston ring and a eccentric type. Could some one tell me about these two types of rings . Are they still used in engines Or were they replaced by the newer piston rings that we use now. thanks Lonnie

[Elden DuRand]

Someone else will have to give us the reason for eccentric piston rings. I knew at one time but forgot (Ain't gettin' old fun??!!).

I Do know that they aren't used any more.

Also, today a lot of oil control rings are made of steel.

Take care - Elden
http://home.cybertron.com/~edurand

[PistonRing]

Hi Elden and Lonnie-
The eccentric rings are pure 1920's and before technology. The problem was how to make a piston ring that was round in the cylinder when compressed and could be turned round on a lathe at a larger diameter so that when the gap was cut out the ring would seal all the way around. The solution of the day was to shift the casting away from the gap when turning it. The result was that the pressure around the ring was adjusted thus "warping" the ring back to round for the desired cylinder diameter. This caused the rings to have a weak seal near the gap since the bottom flat side was thin in this area. The bottom flat side is a critical sealing surface for a piston ring and is the problem area of rings not sealing in worn grooves. Newer technology featured eccentric turning of the OD and ID of rings before splitting the gaps thus leaving a concentric ring that was round for the cylinder bore. This is what is used today. Remember, square pegs won't seal in round holes. Steel oil rings are just a use of a material better suited for the job at lower cost. I am not aware of anyone today making eccentric rings. If you encounter eccentric rings in an engine they are likely old rings made before 1920 and are probably the original rings that came new in the engine. I still have a few NOS eccentric rings on the shelf in a few obscure sizes but these are far and few between. They have been collecting dust for 80 plus years.
Thank you,
Dave Reed
Otto Gas Engine Works
2167 Blue Ball Road
Elkton MD 21921-3330
phone 410-398-7340 http://www.pistonrings.net
http://www.pistonring.net

[Lonnie Grissom]

Thanks for the lesson. I do learn a lot from this board. Lonnie