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Home> Maintaining your Continental and Lycoming engine Piston Ring RotationDo the piston rings rotate during engine operation?
This question comes up now and then so here is a method of showing that yes, the piston rings do rotate Turn the question around and ask what would happen if the piston
rings did not rotate?
Lets take the position that the piston rings do not rotate. At the top of the piston travel there is a area where only the top piston ring reaches. If the top ring is not rotating there will be a small gap in the wear corresponding with the gap in the piston ring. This gap looks something like the wear point A (only reversed) Likewise, at the bottom of the piston travel where only one piston ring rides, you will also see a small gap in the wear from the corresponding gap in the piston ring. If we do not see a small gap in the wear at the top and the bottom then the top and bottom ring gaps are changing position which means that the rings are rotating (not spinning). Another way to prove this is to make a cylinder wall so rough that the piston rings are locked into position. Run the engine and then take a look for yourself.
Piston showing gap in the bottom oil control ring How fast do the piston rings rotate? Quoting from one study: "Rate and direction of piston-ring rotation varied with cylinder-head pressure and engine speed. Rates of rotation as high as 1 rpm at an engine speed of 1000 rpm were observed."1 1.
Report No. 850 National Advisory Committee for Aeronautics, Aircraft Engine
Research Laboratory, A
visual photographic study of cylinder lubrication, 1946 Shaw, Milton
C Nussdorfer, Theodore
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