What's the Best Reed for Cox Reed Valve Engines.

Mr. Dan,
I've read, but not experienced, that floppy disk material can make a good reed. I know finding a floppy disk may be rough in this day.

I can send a few square inches of 3.5" floppy disk (not counting the case), if you would like to try it. I should have your address from the Cobra project. Give me a few days as I'm in GA right now.

Jim in NE MS

Thanks for the replies gentleman!! I'll let this ride for a while and see who else has anything to offer. I still have to go through more of my parts boxes to see what I may have. I do have some teflon reeds, that I probably got from Davis Diesel. I have some others from what I think are polypropylene ( has P.P. on the little white envelope ) and what may be the three different reeds that Ken is describing. These are in a small, squarish white envelop. I have a supply of some old floppy discs that my brother gave me several years ago, so I'm fixed up there. I need to get my micrometer of snap gauge out to measure thicknesses more accurately, but from what I saw to night, the teflon was thickest at .005" or .006". All the others were between .001" and .002" If I need to take the star reed out, the teflon reed will get a test next. The test run in the drive way sounded much better, and I hope to fly it again tomorrow if the weather cooperates. The airplane is an ARF model, and had some control issues that I think I have worked out, and last good engine run I had I was able to fly a pretty recognizable pattern. I hope to test other props tomorrow also. Right now, a Cox 5X3 black flexi prop is doing good work and I have some gray 5X3s also. I have a selection of others from APC to try also.
   here are some photos of the stainless reed I pulled out of it. These are not a great grade of stainless, if that is what they are supposed to be, as it is magnetic. Something with more nickel or chromium my be less likely to distort, but I was surprised to see it when I took it apart.

  This is the front side, facing the engine case. You can clearly see that it is distorted.
   








And this is the back side, facing the needle. This is after 12 or 15 runs, maybe more




Again, thanks for the input. Much appreciated!!
Type at you later,
Dan McEntee

Regarding the rpm-s achievable with COX reedies, see my flight video with a red postage stamp product engine having No1 cylinder and beryllium reed, the only non-stock part being a Kamtechnik head,  turning the prop at 28k+ in the air, in defiance of the common belief, that reeds cannot float fast enough to support rpm-s way above 20k.

Old stock reedies with the circlip retainer will or will not work well with reeds other than the beryllium star. The later mylar, teflon and stainless steel reeds tend to be too thick in my experience and will not move freely behind the circlip. It is the tip of these reeds that is pressed down by the circlip, not the center area, where the tab of the clip is jutting out into the crankcase a bit to allow reed movement.

I know there were circlips made by COX of thinner wire too, that would allow a better accommodation to these later reeds without getting their tips pressed down, but they are a chance to find.

https://www.coxengineforum.com/t13833-quickie-100-rc-flight-video?highlight=Quickie+100

Hi Dan, I thought I'd share a recent experience with you regarding the use of the newer/grey "Surestart" backplate/carb assy. The ones that I have.. use the "snap-on" type of reed-retainer.



I was bench-running with an oblong/mylar reed.. (these mylar reeds came installed in the carb/choke-tube assemblies which I purchased from Cox International) while peaking-out the engine and running a flywheel test.. the engine sagged and "bound-up". I thought I'd seized it.. or ruined it.. but disassembly revealed that the "cap" had popped-off and jammed the crank-pin.. ...........

Now I don't know if it was on tight to begin with.. or whether the reed blew it loose due to the excessive RPM's.. or a combination of both. Just thought I'd mention that.. because you're using the same type carb.

What's the thickness of the steel reed that was in there? As I stated; mine all came with Mylar reeds that are .005" average thickness. You might have trouble running the thin-copper star-shaped reed in that carb. I'm thinking that you might experience "reed-float".. if it even seats on the piston's down-stroke. Let us know how that goes.

Here is an update on yesterday's flying. Using the beryllium reed didn't work out well, and after several flights, i am pretty convinced that the runs I was having were affected by the reed, as in looking at it after I took it apart, it got deformed like the stainless reed did, and it dis not fit the surface on the intake as well. The needle settings were not very consistent, and the model tended to lean out after take off. This was interesting because fuel consumption went down to less than 5 minutes for the 1 ounce tank where I was getting between 6 and 6:30. I was able to try some different props after flying with the Cox 5X3 black flexi prop. I tried a APC 5X3, and the engine did not seem to like that prop. RPM went up but speed went down. As i was ready to pack it in for the day, I tried a 6X3 Cox black flexi prop, and that loaded the engine better, fuel consumption went back down, and the run was steady, but whenever I tried to pull up into a maneuver, the engine sagged and even quit on one flight. It's amazing how props all seem to run different on these small engines.
 I took the engine apart again last evening, and saw the reed deformed much like the stainless reed. After removing it, where the sealing surface left a witness mark on it like it did on the stainless and I could see that it wasn't 100% covering that surface, and maybe it was leaking a tiny bit. Then the thought of the reed floating that has been mentioned came to mind. I came to conclusion that the beryllium should not be used in the late model plastic retainers. I think t the design is Ok, with maybe one exception. When I compared the sealing surface of the venturi to some other, older 'horse shoe" or "horse collar"  back plate/venturis, I could see that the venturi was bigger, and that the sealing surface stood higher above the grove that goes around it and between the outer surface. I think this may be a source of the issue with deforming the thinner metal reeds. The beryllium and the stainless reeds are both .002" thick by my micrometer. After reading the above comments, I checked out the plastic reeds i have. The plastic reeds in the package marked "P.P" are .008" and .007" this, and the third is the stainless at .002" again. The Teflon reeds were .006". So, I put the engine back together with the teflon reed and we'll see ho that works. I did have some reeds shaped just like the beryllium star reeds, but decided not to try them since they do not seall 100% of the surface.

    My nest thing to try will be a complete change of backplate to one of two that I have that were packaged like they were an aftermarket product, maybe from Dale Kirn?  Years ago I had bought a box of stuff at a toy show that contained a complete Cox PT-19 and some other Cox parts and some parts boxes. Inside the parts boxes were all sorts of Cox performance engine part by Jerobee and others I assumed came from KirnKraft. They are while plastic, with aluminum needles with a finer taper, mounting screws, installed beryllium reed and wire clip, neatly wrapped in a stapled plastic bag. i have been saving those for a special occasion and this may be it if I don't get the results I need from the Teflon reed. The picture I am posting with this shows three back plates, the more recent gray , an older red one, and the white one I mentioned, along with the two metal reeds i ran in the gray plastic venturi. This photo shows the difference between the gray unit and the white and red ones. The venturi hole in the gray venturi is .175" while the others are .165" and that may hurt performance a bit, but time will tell. That is one reason I tried the Teflon reed first in the gray venturi. I also took a spare needle from the gray back plates and tapered the needle just a little bit more to sort of match the aluminum needle. I found some Mylar material that is .010 thick or so and may try making a reed from that, and will looks for any other Mylar material I think I may have that is closer to .005". I think that may be the optimum thickness. I also had the thought of trying to make some hard aluminum reeds, as I don't recall anyone doing that. I have some printing plates that are .005" thick or so and will try that. Printing plates are a hard aluminum to be able to take the pounding they do in a printing press and do not form or fold well because they can crack. I think sheet metal guys call aluminum like this 'quarter bend" because any more than a 45 degree bend without a substantial radius will crack. Soda and beer can stock is a harder aluminum and about .005" to .007" thick, and is cheap and  plentiful. Also will make some of the floppy disc reeds.
 Thanks again for the feed back, and jump in any time with any other ides or suggestions.

 Type at you later,
 Dan McEntee

 These are the possible aftermarket horse collar back plate assemblies. I don't think they are Cox factory parts or they would be in Cox bags



  These are the three backplate/carb  examples I have been looking at. You should be able to see the difference in where the reeds seat , and the hole diameters. Notice below them are the stainless and bryllium reeds I have run, and how close the polish marks run to the edges of the beryllium reed/
   

getback wrote:Hey Dan , you want like the Teflon reed tried them with not that good performance and had one fold . The note books with the binder that have that mylar cover are .005" and will work I have used them alot . Bernie from Cox Intern. might would know , its seem to me the 3 pack you could get at one time Ken spoke of had a crystal (what they called it ) reed in it it was a trial pack was a very good reed stiff it was and gone they are ! I see the difference in the holes you speak of that gray one will only work with the reed holder that plastic cap .
I hope I got that right lol but seems .002' is going to bee to thin , seems that red plate will bee your best bet . Interesting I hope you get it figured I been reading on this whole thread .            

It will ne nice to get something figured out that will perform well and be consistent and durable. I haven't even looked at what Bernie and EX Engines has to offer yet, trying to use what I have on hand. I would like to be able to use these gray engines because I have so many of them, and the reeds are the only questionable part, really. The first one I tried on this Baby Clown must have been defective, and it went south on my after just a few flights. I took it apart, and found that the piston/rod socket was so loose I was surprised that it didn't come apart!! And it literally only had 5 or 6 flights on it at a reasonable RPM and prop load. I reset the socket as per normal, and had a nice clearance in it, but the engine just would not run right after that. It seems to bind and catch a bit at the bottom of the stroke, and I had not ever seen that before. I just grabbed another engine, did a few careful break in runs on this one, and it's been OK except for the reed issues. The weather is cooling off here now, and just need the wind to cooperate to tests fly. Thanks for the heads up on the Teflon reed. I'll report back on what this one runs like. If any more problems arise, I'm going to use the red back plate, set up like the white ones, since I have all of those parts on hand.

Type at you later,
Dan McEntee

Hey Dan, Here's a few photos of my reed-stock.

Below photo is of a mailing-envelope which has some measurements that you might find useful.



I found (as Eric/getback mentioned..) that .005" thickness plastic-sheet can work well for making reeds for use in the carbs that have a "cap-style" retention system.

I also like to use what I have on hand and used a circle template to lay-out my homemade reeds onto some random .005" plastic-sheet that I had. Check plastic packaging that you'd ordinarily discard in the trash.. to see if there's a flat piece that's near that thickness. You may have enough for a lifetime supply of reeds.





There's a few different ways to make the shape.. and I honestly don't feel that it's imperative to have them be perfectly symmetrical.

I use ordinary household shears to cut-out the pieces.. and for making the star-shaped reed; I just "nibble" semi-circle cuts using a hole-punch.









If your carb uses a circlip reed retainer.. be aware that the "wire-size" (diameter) can vary. Many modelers don't understand how much this can affect the function of the reed. My circlips vary as much as .005" in wire-size/diameter. (see my photos below) If I had to guess why; I'd surmise that when Cox later changed to the thicker Mylar reed.. this required a smaller wire-size to prevent "pinching" the reed against the housing.. which would prevent its functioning. The "blow/suck" testing-method should reveal a reed that is pinched.







It's in your best interest to "measure" the wire-thickness using a precision instrument.. and separate them into small bags/envelopes marked with their size for future reference.

Yes, the socket felt really good to me. It had just a hint of endplay and rotated easy. It was REALLY had to get it that way, like there was too much metal in the socket. I don't think I ever had to hammer one as hard as I did that one. That's OK, I can still use lots of the other parts. The gray engines that i have all , so far, have had the stainless reeds. I remember tinkering with these as a kid but never had the problems with the reeds like these do, and I think it's because of the way the surface of the gray plates are made. Cox was probably just using up what they had to assemble them and then clearing them out, so you just have to learn to deal with it. mix and match parts to get something that runs!
Type at you later,
Dan McEntee

Hi Roddie!;
Thanks for the pictures. My stuff is not very organized but over the many years I accumulated things, I'm sure I have a variation of a lot of things. I read about the different clip wire sizes also somewhere else. That might be a winter project, spend a day just sorting, identifying and separating parts. The dimensions and tools for making the reeds will be handy also. Thanks for posting!!
Type at you later,
Dan McEntee

i spent some time practicing to cut some reeds from a floppy disc. I took a short length of 15/32" round brass tube, chucked it in a drill, and filed one end down to about .457" I sharpened the end like we would for punching holes in paper or balsa, and used that to cut some discs out by putting the floppy on a cutting mat sitting on a firm surface, and then tapping the tube with a hammer. it would make neat discs for two cycles or so, then needs to be cleaned up again using the drill.. Then I just laid a stainless reed across it, evened it up and sliced the sides off. The put each one in a back plate and tested it with the suck/blow test and I'm in business. The floppy discs I have are .003" thick. I finished the Diet Pepsi I was drinking and cut a piece of can out to measure and it's .004" thick and pretty dog gone stiff. I did not cut any from the aluminum stock yet. This reminded me that I have some colored plastic shim stock from when I worked in the printing business as a maintenance tech. We used the plastic to shim print units to their final height and level them. Some of these print units weigh about 25,000 pounds, and when I measured this material after taking old presses out, I measured it against the known thickness and it did not crush at all!! The neat thing about this shim stock is, it's color coded and goes down to .0005" and up to .010" in .001" increments !! You could make reeds in several thicknesses and tell them apart just by looking at them. The shim stock is made by Artus Corporation and they specialize in this kind of product along with gasket material. A sheet of the .005" material is colored blue, and a 5" by 20" and costs less than 5 bucks!! I have an email in to them asking what type or plastic it is made from, just so I know, but from what I have seen of this stuff in person on the job and in use, it's pretty damn tough!! I made a reed out of the blue .005" stock and it will be the next to get tested if the Teflon reed in the engine now does not perform up to snuff. I'll keep this thread posted.

And again, roddie!! Thanks for posting those photos and the information!! It really helped out a lot!!

Type at you later,
Dan McEntee

Just a little more info. on reeds Dan.

Roddie's Redneck Reed thread

Experimental Reed-Valve Test