I think quite a few of the Cox reed valves work just fine without springs, but it may depend on the actual reed material. The stainless steel reeds seem to just be captured by the plastic retainer--as far as I can tell there is no "spring" involved.

I'm guessing Larry Renger would be the authoritative voice here.

Reviewing the Cox reed valve engines I hav, there are two distinct types.
Original design had the red retained with a wire clip that sets in a grove in the plastic and the second type has the reed captured by a plastic cap.
Clancy

Thanks all!

I'll try it as is and see what happens.

Sorry, I just noticed this thread.

The reed is supposed to float freely, not be sprung against the seat.  Air pressure either way is supposed to be the only force to move and seal the reed valve.  As a kid I thought that the spring was supposed to force the reed shut ...NOT!  Let it float, and it will work just fine, about .020 range is what I remember is the clearence for it to be free.  As long as it can't run away into the crankcase, it probably is just fine.

The old bronze reeds were excellent, the Mylar reeds were even better for the first few runs, but then the heat in the engine would warp them.  We went to the Stainless Steel reeds as a design that worked well at all times for a very long time.  I tested a variety of materials, including thicker and thinner Stainless, and came up with what seemed the best solution for production, performance and durability.

I have ever been a modeler, and kept the needs of the "hard core" in mind as a designer for commercial producers.  Quality would never be sacraficed for a small increase in profit if I had my say (and I may not have let the bosses know the alternative..... )