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Discussion Starter · #1 ·
hi: member, here. i hope my question is acceptable for this forum.

i'm replacing the piston rings on my lawnboy. the new rings are different from what i've seen before (and different from the old rings). i'm hoping one of you can help me to understand the reason for the difference, and the best way to install the new rings.

my mower has a two-cycle engine and uses a piston with two rings. the new ring-set has one ring which has a rectangular cross-section, but the second one has a triangular cross-section [the surface of the ring which contacts the cylinder-wall is about 0.062" and the back surface (inner-most in the groove) is about 0.010"]. in other words, the profile of the ring looks like a 30-60-90º triangle.

i'm thinking that the 60º corner might be there to either:
1) more positively "scrape" the fuel-charge off cylinder wall, or
2) cause the ring to be forced more firmly against the cylinder-wall by the pressure-front in the combustion chamber when the plug fires.

does anyone know, for sure:
1) what the purpose id for the triangular shape of the ring?
2) should this ring be installed in the top groove (closest to the dome) or the bottom one?
3) should the square corner of the ring be installed toward the top of the piston, or toward the bottom?


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