Reed clearance/gap

I searched the threads here; including Paul G's Mouse Racing tips, and couldn't find any definitive info. on the reed's clearance. I feel that there's more to be examined with the way the reed operates.. that will make or break good performance.

As we know; there are several reed materials and thicknesses in use.. as well as shapes.

Materials: (most commonly found) Beryllium/Copper, Mylar, Stainless Steel and Teflon.

Thickness: I assume that the differing thicknesses between the material types is directly related to their degree of "flex".. or they would not differ in thickness. (your thoughts?)

Beryllium/Copper=.001" (.025mm)
Stainless Steel=.002" (.050mm)
Mylar*=.005" (.125mm) *both star and rectangular shape versions.
Teflon=.010" (.25mm)

Shape: Cross/star or later rectangular, would not seem to matter; as long as the reed's cross section is supported by it's retainer system.. whether it be a spring-steel circlip.. or the later plastic "cap" style retainer. I have only seen the Beryllium/Copper reed in a cross/star shape. I have Mylar reeds in both shapes.. and they are the same thickness. (your thoughts?)

Function: Here's where some discussion will surely ensue (I'm hoping)... The basic function of the reed is to open and close (valve) with each engine stroke, allowing a metered amount of fuel/air into the crankcase for combustion. Like any valve.. it must seal when it closes. At 15,000 rpm.. the open/close cycle happens 250 times/second!

Given the differing thicknesses and degree of flex between the various reeds; their retention system must come into play. Paul Gibeault states that the Mylar reed is necessary for performance and that the star/cross Beryllium/Copper reed will begin to "float" at an rpm far below optimal for a performance engine. I would suspect the main reason to be because of the Copper reed's thickness. The circlip-style retainer that was originally designed for it by Cox, allows the thin reed to rotate freely in it's housing without pinching it at it's OD. The thicker (x5) Mylar cross/star reed is said to provide better performance. Some say that the Mylar type should also rotate freely in the housing while being retained by the circlip. If it will rotate freely without any modification.. this would indicate a clearance of at least .005" under the circlip. Is this why the thinner Copper reed floats at high rpm's? Is it's rigidity (or lack there of..) a factor? (your thoughts?)

Flex: When the reed opens, it must be retained from flexing too far away from the seat. Circlips can be.. and have been mistakenly installed backwards, preventing the reed from opening at all.. but when installed correctly; what is the optimum "gap" for the reed to open? Should this gap be checked/adjusted? It's obviously "pre-set" and non-adjustable on the newer plastic style retainers. I checked two random circlips and found a significant difference in the center gap. Perhaps this difference would only show-up in a slightly different needle-setting? Could less of a gap prevent a Copper Reed from floating at high rpm's? Would more of a gap with "any" reed allow more mixture into the crankcase up to a point where reed-float occurs? (your thoughts?)

I would ascertain the "star-shape" to be a better/smoother flowing reed.. (as opposed to the rectangular shape) in any type of housing/holder, having it's 4 symmetrically-radiussed tabs. This reed pulls away from the seat with 360 degrees of suspension-support.. and the mixture passes through/over 4 symmetrical edges which in my opinion; makes for a much smoother flow. The rectangular shape reed by comparison, has two sharp-flat edges for the fuel mixture to flow past.. as well as only being retained on two sides.. 180 degrees apart. (your thoughts?)



A closing question: Could the thin Beryllium/Copper (star) reed be hard-anodized to improve it's performance? Paul G. states that using a Stainless Steel reed will eventually wear the anodizing off of an integral (metal) tanks' venturi mouth. Perhaps this would be a consideration in anodizing a Copper reed? Perhaps anodizing would render the Copper reed too brittle?