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RE: Cox Reed Valve FAQ - 9/13/2007 9:03 PM   
burtcs


 

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I got four of them a year or so ago and they were ok. Loose but ok and the ones I've run, run well. An engine will usually tell you when it need's the ball socket reset becuase it won't start (for no apparrent reason).

When resetting to ball soket of a COX be aware (there's not much you can do about it) that you can expand the piston crown. When this happens the piston will not fit the cylinder anymore. I've managed to lap them back into the cylinder for ok fits but it's an extra step nobody talks about.

regards - Steve B.

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RE: Cox Reed Valve FAQ - 9/14/2007 12:23 AM   
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Status: offline 		Hi Tom,
Here is the Cox instruction sheet.
Al

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RE: Cox Reed Valve FAQ - 9/14/2007 9:10 PM   
TGC



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ORIGINAL: burtcs
... you can expand the piston crown. When this happens the piston will not fit the cylinder anymore. I've managed to lap them back into the cylinder for ok fits but it's an extra step nobody talks about.

regards - Steve B.


I'd like to hear more about "lapping", Steve.

Years ago, I bought a little bag of white powder (say what??? ) at a Swap Meet ... says Lustrox, Fox part #90811 on it. I remember putting a little bit of it into a Fox 35 and bench ran it ... it frothed and foamed like a rabid dog for a little bit, but my recollection is that it really cleaned things up.

Thanks, Tom

.

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RE: Cox Reed Valve FAQ - 9/15/2007 12:13 AM   
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Status: offline 		Tom that is a great story I have to remember that. I think the way the instruction go is to put 1/8 teaspoon of powder and 5drops of 3inone oil and mix to a paste like consistency. remove head and with the piston at the lower end of travel place 1/4 of the mixture in the cylinder turn the propeller 100 turns then using glow fuel wash out the cylinder. a combination of pouring fuel and using cotton swabs to clean out the cylinder and clean the piston should do it If there is still a dullness to the cylinder repeat as needed using as much as you may need. when the cotton swab comes out clean finally put the head back on the motor fuel and start as normal run at least three tanks of fuel thru the motor to complete break in once more. dray


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RE: Cox Reed Valve FAQ - 9/15/2007 9:21 AM   
burtcs


 

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I remember that stuff. When I was in Veit Nam I had a Fox 36X that was too tight for comfort and I bought some of it from Fox. I don't recall running it, just coated the cylinder and hand working it back and forth with Fox's blessing. It loosened thing up enough to start. (I still have that engine, and I can still light it up.) It struck me then as Comet (or BonAmi) cleanser or tooth powder, which would do the same thing.

That was lapping but currently I use different compounds and I suspect they work much more effceintly than tooth paste or cleanser. I use 800mesh and 2000mesh compound (Clover brand, which you might find locally at an Industrial Supply house. Some time ago I had the need for speed which a dirt commond 049 Tee Dee couldn't acheive. So being a cleaver modeler I ordered some KK Tee Dee's, these were hot rodded and would typically run 22k-24K with a 5-3 rubber ducky and 60% nitro out of the box. They solved the problem (partially) of yarding a PIG (mybad) freeflight model into the sky. But, they caused another problem with maintainance. The ball socket would be loose (Imean really loose) after about a dozen or so short runs (fifteen seconds or less). I got a ball soket reset tool and base and started reseting the ball sockets. I had no choice. Everyone claims this loosening with stop, I never seen this.

There is a dark side, as I noted you can expand the piston so that it won't run in the cylinder any more (it only takes a ten thousandth or so). Hence I aquired a lapping tool and was able to refit the piston back into it's cylinder. Once you have one of these things you don't have to put up HP robbing friction in any COX engine. Unless you want to (yes they do start easier with the friction there). Your sure Start may not have been a problem to begin with (you may have lucked out) because sure starts have loose piston/cylinder fits to begin with. The four specimen engines I got from COX didn't have loose ball socket joints but they did have loose piston/cylinder fits and the starter spring makes life easier.

So...to lap a piston/cylinder you will need:

the lapping tool
lappng compound (800-2000 mesh) this is NOT valve grinding compound.
a tooth pick
one or more facial tissues (kleenex)

You assemble the tool on the piston and tighten it up so you can use it. This provides you with a hand-hold on the piston (and rod).
Now I am left handed so do what you instinctively would do, I grap the piston/tool in my right hand, with a tooth pick apply a small (just a dab) amount of compound to the top edge of the piston and turn it into the cylinder with my right hand ( or keep turning till the
piston re-enters the cylinder). I gently screw the cylinder onto the piston, pausing at tight spots for complete turns and then move on when they loosen up and I can do so. I only turn the piston one way. The piston gets tighter at the top of the cylinder. You can stop here and break the engine back in or you can remove the tight spot by turning the piston out of the top of the cylinder. Your call.

Once you have some compound (preferably a small can cause this stuff goes a long way) you can loosen up threads, fit pistons and generally wear things out fast. You will have to use a tissue to remove all traces of lapping compound. Don't be bashful about swishing things around in a can of alcohol.

Well there it is, aren't you glad you asked. Having said all this, lapping removes metal it doesn't put it back on. This works with COX engines, they have steel cylinders and pistons for the most part. Piston fits in ABC type engines can also be done though outcomes are fussier.

regards - Steve B.



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RE: Cox Reed Valve FAQ - 9/15/2007 11:23 PM   
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Status: offline 		...... For a really great article on it try the June 2005 issue of Model Engine Builder. On page 7 Ken Croft will tell and show you how to lap a piston to a cylinder......

< Message edited by BMatthews -- 10/16/2007 6:50 AM >


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RE: Cox Reed Valve FAQ - 9/16/2007 7:31 AM   
burtcs


 

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Status: offline 		Clover makes a good many compounds. If you go to their web site you can check them out.


< Message edited by BMatthews -- 10/16/2007 6:54 AM >

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RE: Cox Reed Valve FAQ - 10/4/2007 2:04 AM   
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Status: offline 		Here goes. I have 2 Reed valve engines and have not run either yet. During the dissassembly and cleaning I noticed the spring holding the reed valve to the backplate is adjusted differently on each of them. One has the flat part of the spring directly in contact with the reed the other has a gap. What should I do before putting them back together? My goal is reliability and low maintenance. Thank You . Jeffie

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RE: Cox Reed Valve FAQ - 10/4/2007 4:47 AM   
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ORIGINAL: jeffie8696

Here goes. I have 2 Reed valve engines and have not run either yet. During the dissassembly and cleaning I noticed the spring holding the reed valve to the backplate is adjusted differently on each of them. One has the flat part of the spring directly in contact with the reed the other has a gap. What should I do before putting them back together? My goal is reliability and low maintenance. Thank You . Jeffie

The little reed is supposed to flutter in and out with the crankcase pressure fluctuations, and thus needs to be able to move outwards slightly. The spring is needed to keep it in place rather than pin it down.

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RE: Cox Reed Valve FAQ - 10/4/2007 5:32 PM   
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Status: offline 		I agree. Looks like someone put the little clip spring in place upside-down. Put it back together, and put a piece of fuel tubing on the needle valve assembly...where the fuel line usually goes...then blow gently and suck gently on the fuel tube and you should see the reed move up and down. It only moves about the thickness of the reed. This works on the Surestart and other product engines. If your engine has an integral fuel tank, just put the reed back in place and put the clip back in, and pick at the reed with a pin or needle to be sure it moves up and down. OKAY...now here's MY question: Are reeds different thickness? Will the spring clip for the copper reed work with the floppy disc reed...or the almost clear plastic almost oval reed?

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RE: Cox Reed Valve FAQ - 10/4/2007 7:52 PM   
aeomaster32



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I agree. Looks like someone put the little clip spring in place upside-down. Put it back together, and put a piece of fuel tubing on the needle valve assembly...where the fuel line usually goes...then blow gently and suck gently on the fuel tube and you should see the reed move up and down. It only moves about the thickness of the reed. This works on the Surestart and other product engines. If your engine has an integral fuel tank, just put the reed back in place and put the clip back in, and pick at the reed with a pin or needle to be sure it moves up and down. OKAY...now here's MY question: Are reeds different thickness? Will the spring clip for the copper reed work with the floppy disc reed...or the almost clear plastic almost oval reed?

I think so, because I have had no trouble with a teflon reed which seems a little thicker. As long as the reed stays in place, and can move enough, it should be OK. If not, you can always open up the spring a bit.

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RE: Cox Reed Valve FAQ - 10/14/2007 5:51 AM   
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Status: offline 		I don't like to see the word "venturi" used in connection with Cox reedies. The narrow section is before the space that the jet opens into. In the metal tank backs the jet is on top of a larger section, and the Surestart has it at the back of a bar. My Tee Dee 049s do have a venturi, with three jets opening into it. The reedie carburettors operate more like the choke or or idle jet of a car. The decrease in pressure is from reducing the flow into the space, not due to Bernoulli's principle.
I think this helps to explain why the reedies are so much easier to start than the TD. It certainly helps to explain why the TD is more powerful. In the TD, as for the main jet in a car, the pressure drop is in a venturi and is due to Bernoulli's principle. That is, the flow lines coming into the carburettor are concave outward, so that the momentum of the air pulls it away from the walls of the aperture. (The usual explanation involves the conservation of energy, but this seems more intuitive, when we don't need to calculate the magnitude of the pressure drop.) This reduced pressure draws in the fuel through tiny jets. So the fuel flow is caused by a momentum effect and resisted by viscous fluid friction. The momentum of the air is proportional to its velocity, and the time rate of change in momentum to the momentum divided by the time it takes it to change, so the pressure drop is proportional to the square of the flow rate. Viscous drag (very low Reynolds number) is proportional to the first power of the flow rate. So the TD has too lean a mixture, except when running full speed, and is hard to start. Like a car would be with no choke or idle jet.
The reedies are easy to start, because the flow restriction ahead of the jet is also viscous, so the mixture is roughly independent of flow rate. Of course, restricting the flow reduces the power.
I think I am using the word venturi correctly, as my brother, who is a professional racing mechanic, said he didn't see a venturi either, when I sketched the reedie carburettor for him.

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RE: Cox Reed Valve FAQ - 10/14/2007 7:43 AM   
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Status: offline 		I suppose the reset tool expanding the piston is an advantage, unless the fit is already tight. I was able to lap the pistons back to fit the cylinders on my Tee Dees until they would start, without adding any abrasive, but I have read toothpaste and Bon Ami suggested. Other possibilities might be Brasso or car polish. (With things like toothpaste or silver polish, one could use a water soluble lubricant such as liquid detergent or KY.) If it wouldn't fit in even to hand lap, I would try 600 or 1500 sandpaper, curved around the piston, or maybe see if I had a looser cylinder that I didn't need.
I had one of the TD cylinders on a Black Widow. With the Black Widow more constant mixture carburettor and the TD extreme sub-induction, I had to put my finger over the intake to keep it from running away.
Sometimes the rod small end would not turn freely anymore in the piston, so I wiggled it too, until it would.
Has anyone tried making his own reset tool out of wood or metal? I don't have an 020 reset tool.
I think it must be better to reset the piston early on than to wait until it causes problems; the play must make the play increase faster.
The Cox instructions say it is needed less when the fit gets looser, but the Davis Diesel instructions say that is because of work hardening rather than fit. (So the piston must have a finite lifetime.)

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RE: Cox Reed Valve FAQ - 10/16/2007 2:02 AM   
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Status: offline 		I have achieved 18500 rpm with a Surestart using a stainless reed and a 5x3 prop. Had the same results with a mylar reed. The mylar reed does thumbnail quickly but is still useable. I have yet to try teflon, I have some so I will be trying it.

My belief is that correct compression and the ability to breath is more important than reed material, without going to shortening pistons and SPI. Reeds are reeds.

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RE: [Deleted] - 10/16/2007 7:10 AM   
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Status: offline 		OK, the thread has been pruned of a lot of various side discussions and wandering theory into what I hope is the bare bones material that will help folks tune and maintain their reedies. I cut out a lot of stuff that while interesting doesn't really pertain to just keeping these engines in good order.

At this point the thread is locked to prevent any further wandering of the core topic. Questions that arise from reading the info here should be asked in a new thread. Or if someone sees any new techniques or info that they feel is worthy of including should PM me and I can add the material as quotes from the other thread.

Thankyou to all that contributed to the thread both as resources and those of you that asked the questions in the first place.
Bruce

< Message edited by BMatthews -- 10/16/2007 7:11 AM >

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RE: Cox Reed Valve FAQ - 11/8/2007 4:24 AM   
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Status: offline 		As requested from another thread this has been added.

If it helps when I'm choosing my pistons to cylinders I generally look for the loosest and leakiest fit that isn't leaking from a bad deformation or score. The sloppy fits seem to run best and that occurs when a dry piston can fall cleanly through a dry cylinder. With 3in1 oil in it and with a complete engine if I put it to TDC it should bubble out the exhaust for around 3 seconds at most. If it leaks down to normal in less than a 1/2 second then it's a little TOO leaky. A leakdown of 1 to 1.5 seconds seems to let 'em sing reeeeeel guuuuuud....

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RE: Cox Reed Valve FAQ - 11/11/2007 7:45 AM   
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Status: offline 		Here's a sketch I made of a reset tool for the 049's. As shown it's intended to be a lathe project but I first made one years ago using a cut down 5/16 grade 8 allen cap bolt. The hole and countersink can be drilled using a drill press or with a bit of care even a hand drill. The conrod slot can be cut using a set of 3 hacksaw blades stacked together on one frame to make it into a slotting tool for this project.





< Message edited by BMatthews -- 11/12/2007 12:11 AM >

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RE: Cox Reed Valve FAQ - 2/14/2008 8:25 PM   
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Status: offline 		Here is a Cox advertisement with an exploded view and description of an early Babe Bee engine. Note the round runway below.

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RE: Cox Reed Valve FAQ - 4/6/2008 9:22 AM   
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Status: offline 		if you check on ebay there is a guy who sells the reset tool for a few bucks, I bought one for a couple of project engines that needed the tightening at the rod it worked well, comes with a anvil and conical rod as well as instructions.
was reading along and still didn't see a answer for repairing mounting holes,I did try using the JB Weld,on a beater back plate,that was destroyed by a shipping Co. and it seemed to be pretty sturdy,but any other ideas would be great to hear since these are getting harder to come by.

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RE: Cox Reed Valve FAQ - 4/6/2008 10:24 AM   
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Status: offline 		If the tabs are broken off but you still have a bit of a U shapeshowing you can still use screws to hold them in place. Just trap the ears of the remaining U as best you can. They only pull a few oz of thrust at best so as long as it can't shake itself out of place you're OK.

Being pot metal there's not much you can do.

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RE: Cox Reed Valve FAQ - 4/12/2008 11:26 PM   
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quote:

ORIGINAL: bigtim

if you check on ebay there is a guy who sells the reset tool for a few bucks, I bought one for a couple of project engines that needed the tightening at the rod it worked well, comes with a anvil and conical rod as well as instructions.
was reading along and still didn't see a answer for repairing mounting holes,I did try using the JB Weld,on a beater back plate,that was destroyed by a shipping Co. and it seemed to be pretty sturdy,but any other ideas would be great to hear since these are getting harder to come by.



I just got the reset tool, it works great. I really never paid attention to the rod and piston on Cox's before.

I just cleaned out a new SS I just got. There was a lot of metal dust/shavings in there . I tried to filter it to take a picture but I don't think you would be able to see it once posted. Anyhow I'm all set now, I just need to build something for it .


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RE: Cox Reed Valve FAQ - 7/5/2008 8:03 AM   
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Status: offline 		Hello,
A quick question. The copper looking reed valve is damaged, can these still be purchased? Or better yet can I make one out of certain material?
Thank you

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RE: Cox Reed Valve FAQ - 7/12/2008 11:09 PM   
jetpack



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Status: offline 		You can make one out of an old floppy disc from the mylar disc that's in them, and there is Davis Diesel Development (D3) which sells teflon replacements.

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RE: Cox Reed Valve FAQ - 7/13/2008 1:29 AM   
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Status: offline 		I have a number of floppies around here, so I traced the copper reed valve with my hobby knife and it worked out very well.
Thank you so much jetpack.

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RE: Cox Reed Valve FAQ - 7/13/2008 1:39 AM   
jetpack



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Status: offline 		I have cut out a few for spares but haven't tried any yet, but have read it's a good replacement for the copper. Seems a bit more lively than the copper, and might wear a little faster...but performance-wise I don't know if it's a hop-up or not on RPM's. Reeds play a big part with these engines, and even slight changes can be noticed.

One thing I've always kept in mind when working with reedies is trying not to touch the reed after I've run it unless it's really necessary because they seat themselves in and it's not good to move it.

Besides the star shape I would cut a few of the oval kind too. You might not have seen them but they are shaped like a Band-Aid. I think someone said that shape works better with the floppy. Don't know myself. If you don't have one I can measure one up.

I used the forum search and found this link how to make reeds.

< Message edited by jetpack -- 7/13/2008 1:54 AM >

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