The aftermarket non-Tecumseh made rings I picked up has a first compression ring that is about 10 thousands thinner than the original.

The end gap spec is 10 to 20 thousands. The new ring end gap is 9 or 10 so just at the good side of in spec. The old ring is 24 thousands so out.

The diameter puzzles me. What is the effect of having a ring that is that much thinner? It seems the thinner ring will have to rely more on it’s own spring tension to keep expanded against the wall of the cylinder. I would think that the thicker ring when new had a much easier time of keeping against the cylinder wall and do that for more years. ??

Is this a difference due to a cheaper aftermarket part or a design difference?

David http://www.kedawei.com/snowblower.htm

Ring "side" gap is has a definitive effect on engine operation. When you say "thinner," I can only assume you mean top to bottom thickness, rather than outside to inside thickness.

If the ring is thinner top to bottom, then ring flutter will occur.

The gap designed into the ring land to ring space allows compression and combustion pressures to get behind the ring, forcing it out to provide the proper seal.

The sole pressure of the ring's outward pressure is insufficient to provide the necessary seal. Having a ring-land excessive clearance usually prevents the proper pressure seal (ring twisting can even occur), and ring flutter occurs allowing a loss of combustion pressure and allowing "flame wrap." All hell breaks loose then...this would be the death knell.

End gap, measuring the gap the rings leave when put in the cylinder and pressed in with the piston upside down. When I take that reading with the new rings I get a 9-10. The specification say it should be 10-20. The old rings are 24 so out of spec.

While looking at the rings I noticed that the new first compression ring was "thinner". That is in the plane of 90 degrees to the bore. It's a little difficult to indicate the correct thickness.

There is the thickness in the horizontal direction, 90 degrees to the bore. There is thickness in the vertical direiction paralell to the bore. I'm trying to describe the thickness of the ring in the 90 degree direction.

My question was what difference does it make to have a ring "thicker" than another in the horizontal direction? The new ring is 10 thousands thinner than the old ring. The only reason I mentioned end gap is to indicate that it's the right ring and matches the spec.

Okay, I think I got it. The new rings are thinner as looking from above them lying flat on a table.
The only thing I can tell you about that is if the support isn't there, they could twist in the land and allow blow-by.

If ring-end gap isn't sufficient, once warmed-up the ends could butt up against each other can that can cause the ring(s) to loose their sealing capabilities or break.
0.009" to 0.010" you're reading sounds okay. You could file the ends slightly to open them up to a loose 0.010" to add a comfort level. If you don't support them well when filing, well, they're cast-iron you know...

For what it's worth, I've seen numerous engines running with 0.020" to 0.030" without any major issues, but if the bore is out of round and/or there's piston skirt wear, it'll compound a slightly over-spec ring end gap issue. Most problematic engines I've torn down for failure analysis often had end gaps up around 0.050", and even up to 0.080" (can you say dirt-ingestion?)