profile of piston rings

[Deleted User]

[attachment=0:2cyhzsdn]ring.gif[/attachment:2cyhzsdn]
Hi I’m poundering on the shape of the piston rings from my 29 flyer.
Is has a concave curve on the internal edge of the piston ring. Is it to keep the stress profile the same around the circumference and therefore keeping the wear circular ? and why is the end ground to an angle of 30 degrees ? It is of no consequence because I’m going to take Rodger’s advice and reengineer the piston and rings to take Triumph 5TA rings, but I’m interested to know the thinking behind the design, any thoughts ?

regards Jonathan

[Ian Parsons]

This is really obvious. The angle is to match the angle of the original piston ring stops and the internal radius at the ends is to clear the legs of the piston ring stop. All quite apparent when fitting new rings. Incidentally I buy normal 4 stroke rings and file the angle and relief. I am sure many other owners do the same.

[Deleted User]

OK fair enough , but it didn’t seem that obvoius to me , All pistons rings are not this profile ! 😕 and I was asking whats the thinking behind the design.
Thank you for the reply

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