Soft Piston Rings
I fly a Baby Ace N30051 with a Continental A65-8 engine. This fall I had a problem with #2 piston having two soft compression rings. The oil ring seamed O.K. I have no mixture control. The piston and cylinder didn't look like they have over heated. Compared to a new ring. I would guess the bad rings were at least one half as stiff as a new ring. I have never heard of this problem. Any ideas on how this could happen?
Assuming rings are ferrous (iron/stee)l, the stiffness is a function of the material modulus which for steel is 30MSI and is not changed by heat treatment/hardness. If rings feel softer because they deflect more by hand force, it would lead me to believe rings were made from a lower modulus material. Put a magnet on suspect rings and see whether it's ferrous. If it doesn't stick, must be a non-ferrous or stainless steel material and maybe someone made a mistake at ring factory.
If rings are ferrous, then hardness may be controlled by correct heat treatment and a Rockwell C hardness test would give insight as to strength level. In fact, you might have a hardness test performed on a good ring and the suspect ones for comparison.