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widow giving me fits

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Re: widow giving me fits

Post  GallopingGhostler on Thu May 28, 2015 5:23 am

chevyiron420 wrote:Anyway, I installed a retainer off a spare carb and put the steel reed back in and it runs great. Man this thing about drove me nuts. Taking it apart so many times, one by one all the backplate screws busted through and one by one I sleeved them all. I aint taking it apart again but I really want to know what is wrong with that reed. It looks good to me. Phil
Phil, if you look at the design for the reed retainer on later Cox engines, they use a different retaining system. I imagine that the mylar reed being of softer material must have a clipping system that allows free movement along the edges.

With your particular engine, the metallic reed is of thinner composition and the spring clip allows for freedom of movement, but not with the slightly thicker mylar. It may pass the suction test, but that test is static (without much movement). When running the reed is vibrating at the same frequency as the prop is turning. I imagine there is a certain amount of binding under the retainer spring through vibration, which prevents it from snapping back into place.

Perhaps on other engines, the spring clip is of slightly thinner diameter or groove is wider, allowing more movement for non-metallic reeds.

There is certainly nothing wrong with continued use of the steel, copper or brass reed. Any run improvements are subtle and unless you are in out and out competition, should provide good service with that engine.
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Re: widow giving me fits

Post  getback on Thu May 28, 2015 7:47 am

Great news , as George said and I have ran into this one time on an early bee new Mylar reed from cox inter. and when you put it in it had a bow to it and had to sand it down as you said to fit and work properly , Glad you got her figured out . Mount and fly Memorial Day
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Re: widow giving me fits

Post  chevyiron420 on Thu May 28, 2015 2:03 pm

I looked over the "bad" parts last night and see where I went wrong. When working on something like the reed assembly I have a habit of putting the parts back in exactly where I took them out every time. The reed lays flat and seals good in the location I put it. The problem was the inside of the plastic retainer isnt round. Even though the reed rotated around freely there is a tight spot. Wile the engine was running the reed would migrate around to that spot and bow a little. Then it would lean out and quit. If I had fitted the reed more loosely I probably would not had a problem.

Another thing I saw wile looking for issues with this engine is there is a ring of plastic around the air inlet screen. It stands up so high it cuts off the air flow if mounted to a flat firewall.

I just hope my troubles will save someone else a headache.
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Re: widow giving me fits

Post  RknRusty on Thu May 28, 2015 2:28 pm

Sometimes I dremel an extra air channel in the firewalls even though the backplate isn't supposed to choke it. But in your case it apparently did. Maddening little suckers sometimes. Live and learn.
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Re: widow giving me fits

Post  pkrankow on Thu May 28, 2015 3:39 pm

RknRusty wrote:Sometimes I dremel an extra air channel in the firewalls even though the backplate isn't supposed to choke it. But in your case it apparently did. Maddening little suckers sometimes. Live and learn.
Rusty

I do similar too. I never liked how little area that there is back there. Using a washer behind all 4 screws provides a similar effect.

Phil
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Re: widow giving me fits

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