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Author Topic: Brown A-23 leaking cylinder head  (Read 242 times)
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Ara Dedekian
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« on: April 24, 2022, 11:52:24 PM »



       Does anyone have a fix for sealing the CO2 line/cylinder head interface of a Brown A-23. I've tried cyano, epoxy, RTV gasket material and light cured resin. Nothing adheres to the aluminum head and thats where the leak is. A combo of the resin followed by cyano works the best so far but still with leakage.

       Thanks,
   
        Ara
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g_kandylakis
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« Reply #1 on: April 25, 2022, 02:28:11 AM »

I think I do, but I cannot post the detailed process with pictures right now.

It involves buying some O-ring cord of appropriate diameter, slicing small discs, drilling them in the canter with a droll or a sharpened tube for the copper gas tube to pass through. This is the new seal...

To assemble it you must first cut or fill away the flange end of the copper tubing, remove the old seal, clean up everything and reassemble.

Finally you need to form a new flange, which seems like a difficult task but isn't really. All you need is a 0,5mm wire bent to shape and fixed on a drill to form the flange. Pictures will clarify this...

This produces a result that is as good as new...

More to come...

George
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Ara Dedekian
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« Reply #2 on: April 25, 2022, 05:25:29 PM »


      George

          Thanks for the help. I'm wondering if I'm missing any parts in the head assembly. I don't see how just the flange would hold a charge against the pressure. I've got a B-100 that has the same problem. I'll dismantle the A-23 and post some pictures here. Cutting the gas line and swaging a flange is no problem for me, but where would I put the o-ring that you suggested?

      Ara
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g_kandylakis
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« Reply #3 on: April 25, 2022, 06:19:57 PM »

Hi Ara,

The flange will hold fine under the CO2 pressure. After all it is the same as the original...

Not O-ring, O-ring cord...

The motor shown is a rown 0.005 but the principle is the same. Also, this was my first attempt and like you, I had concerns about strength, plus I did not have a solution for flange forming yet...

That came later, so no more welding...

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g_kandylakis
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« Reply #4 on: April 25, 2022, 06:31:00 PM »

tube end flange forming...

high turns are not necessary, more effective is constant force against the tube, being careful not to bend it...

The cord shown is from a german source, no doubt you can find it in the US as well

I do not remenber the exact diameter and thickness of the resulting seal, but I imagine you can surely measure and calculate it yourself... Quick ckeck, about 3,4mm diameter, about 1,5mm thickness.


It is important to have flat faces for the flange, hence the sanding jig (sand with water...). Also the hole must be snug fit to the tube... sharpen a needle tube and cut with it, as centered as you can.


Try it, very easy and quick to do. if unhappy with the flange, cut and redo. You will see. The gas pressure takes care of the rest...

Any question, just ask... Answer tomorrow, too late now...

George
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khannan
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« Reply #5 on: April 26, 2022, 10:22:19 AM »

Ara,

   I have replacement parts for the A-23's  pm me your address and I will send one these, I believe this is the newer design?
Ken
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Ara Dedekian
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« Reply #6 on: April 26, 2022, 03:44:49 PM »



        George

        Kali Spera!

        Thanks so much for sharing your method of fixing the leak. After seeing pictures of your fix, I did a materials search of my shop for an alternative to O-ring cord and found a dense foam adhesive backed weather stripping. I drilled the center of the plug, slipped it over the flange without cutting it off and stuffed it into the head with the sticky side up. A quick test showed no leaks! I'm sensing that the adhesive played a part in holding the gas in. Further flying and testing will tell if the fix holds.

       Ara
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raggedflyer
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« Reply #7 on: April 27, 2022, 05:27:56 AM »

Couple of comments based on 20 years experience in the cryosurgical industry using C02 & N2O as refrigerants and making joints between plastic and metal tubes at 700 psi, capable of being steam sterilised at pressure and subject to a vacuum drying cycle which is more demanding than the modelling application.

Use a mechanical means such as a screwthread, swaging, crimping to retain parts under pressure rather than solder, braze  or adhesive. Try to employ two joining techniques.

Use an elastomer to provide a leak tight seal such as an o-ring or gasket in silicon, neoprene or Viton or polyurethane sheet.

Take care on the surface finish of sealing faces and edges - leaks will find there way around imperfections sometimes at low pressure or high pressure. Cleanliness is mandatory.

Loctite 542 was (then) the best thread sealing medium for fittings with Loctite 290 fantastic as a wicking sealant applied after assembly to thwart leaks e.g. bubble leaks from fitting threads. So well admired it was known as Jo 90 rather than 290. Must have been Thunderbirds I guess!

If a leak arises it will probably get worse as the parts cool rapidly due to the Joule Thompson effect. Polymers shrink something like 5 times faster than metal. Immerse in slightly soapy water to find the location of leaks. Beware some soaps contain salts that will even promote rusting of some grades of stainless steels.

Spitting of CO2 is a curse of a problem as is water content in the air.

With regards to this particular problem I like the flange retained plate but would try to source a silicon o-ring of the right size using a few percent of squash (look up the o-ring tables). It might be effective to mould a silicon plug in situ using a self levelling grade and pierce a hole through the centre once cured.



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nickpepp
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« Reply #8 on: April 29, 2022, 04:13:50 AM »

Hi Ara,

I had a similar problem with my Brown A-23 when building a Dornier Libelle for the Walt Mooney cook-up. My solution was to fit a stack of three Size Code 001 nitrile O-rings. These have a grip on the copper tubing in the free state. I described this in more detail in reply #2097 (May 12 2020) in this huge cook-up.

Nick
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