Hello:

     Yesterday, I noticed that I could no longer turn the needle on the remote nva of my OS LA .46.  I removed it from the airplane and had to use a vise and pliers to remove needle.  It appears that the rubber seal had become swollen to a point where it would not turn easily.  I tried it in two other bodies and it was evident the it was indeed the rubber seal was too large.  I replaced with another needle and all was well.

     Has anybody else enjoyed the joy of having this happen? Lol Or is it my bad karma that continues to haunt me? Lol

     Comments/remarks?

                                                                                                             Be well,

                                                                                                             Frank McCune

     Hi Tim:

      I got lucky and replaced the “O” ring and all is well again.  The original ring was swollen and was much too large to be able to be moved.

                 
     Thanks for the reply.

     Frank

        Hi All:

        I have only used 5-11-11 fuel since I have owned it.  No oils on the parts.  It performed quite well up to this tlme.

          The rubber O ring had swollen to a point where the entire groove was filled to take a rectangular shape.  It was so tight that I was forced to use a vise and large pliers to turn the needle.  I will test it ASAP.

                                                                                     Thanks for the replies,

                                                                                      Frank McCune

     Hello Again:

      I thought that I had solved the problem of the sticking needle, but once again I was wrong.  I replaced the sealing O ring with a new one and all was well until the first tank of fuel went through the nva.  Once again, there was no way that the needle could be turned!  I even resorted to using pliers but they slipped rather than turn the needle.

       What to do now? The O ring that I replaced the original one with was made of neoprene.  Neoprene is said to be able to stand up well against glow fuel ie neoprene fuel line.  Is there a source of seals for the OS remote nva?  What else can be used?

   What brand of fuel is this?  I checked the engine from the test the other week, and, just like everyone else's, no problem. I used Powermaster 10% "Air" which is 9/9, but there have been no reported problems with GMA, either.

      Brett

     Hello Brett:

     The fuel that I am using is my home brew of 7.5% nitro,11% castor oil, 11%synthetic oil, remainder alcohol.  I hope this helps.

     I will try another new nva to determine if it it is affected by the fuel.
\

  It will be, you have plenty of evidence, don't ruin another one.

     You mean methanol, not alcohol, right?

      Brett

    Hello Brett et.al.:

     Thanks for the replies.  Yes, I meant methanol.  I have used my fuel with these nva in the past with no problems.  I have no idea what is wrong! I am now testing an O ring made of silicone to determine if the silicone will suffice.  Will inform you all of the results.

  There is something else in that fuel making the o-ring swell up and stick, because conventional fuel components will not; there is no special magic that applies only to you. Something real is causing it and it's almost certainly in the fuel, because there should be nothing else around.

    This convinces me even more that there is some systemic problem you have. Before you do anything irreversible, *please* borrow or buy *conventional fuel from a major manufacturer*, like Powermaster 10% "GMA", "Air", or "Heli", or SIG Champion, and start using that. That will give you a baseline that is known to work and remove fuel - which is obviously either wrong or contaminated with something (acetone? coleman fuel? hydrazine? the "Free alcohol"? something else mentioned in these threads over the years?). 

   Brett

  In thinking about this, that O-ring is a seal against air leaking in. Crankcase vacuum is what draws fuel to the NVA and past the point where the needle regulates the flow, and then on up to the venturi, etc.  Any fuel would have to be under some kind of pressure, make it's way up the inside where the needle passes, and out onto the threaded external part of the NVA.

  So, exposure to *air* caused it to swell up and jam?

    O-rings do not just swell up and jam exposed to either air, or normal commercial model fuel components. Therefore it was exposed to things not normally in model fuel. Given that this is home-brew fuel with unknown sources of the constituents, and it *consistently doesn't run properly* as suggested by innumerable previous threads, many of which contain discussions about obscure fuel additives, it could have lots of other things that DO cause o-rings to swell up, the most sensible way to eliminate the fuel as a source of problems is to get a commercial fuel of known quality. 

   What does not make sense is to take a known-good part, and then start modifying it, changing materials, to try to "work around" whatever other problem is present, because there is absolutely nothing wrong with the part as it comes from the factory.  That's stacking a kludge on top of an existing problem. Of course, the next step is to "replace the crummy rear needle with a good ST spraybar", which stacks yet another change, now you have to also change the venturi, or the engine suddenly loses 20% of the power, and also induces the potential for more problems with the known "tuning fork effect".

    That's how these things spiral out of control. The fact that a presumably stock part, known to be good, is getting jammed up tells you beyond any reasonable doubt that there is something odd about the fuel, because that's the only thing this o-ring is exposed to that could conceivably cause it. That's a problem that needs to be fixed, forget anything else, before proceeding to the next step, because whatever it is might also be causing the systematic low power and odd run characteristics that Frank has been experiencing, well, forever.

   Of course, as always, it's just advice, no one is compelled to listen or act on it.

   The red flags don't wave any more wildly than this.

     Brett

Have you soaked an O ring in your fuel out of the motor/NVA?  What does your fuel do?  But I fly electric, so just asking.

  So, exposure to *air* caused it to swell up and jam?

    O-rings do not just swell up and jam exposed to either air, or normal commercial model fuel components. Therefore it was exposed to things not normally in model fuel. Given that this is home-brew fuel with unknown sources of the constituents, and it *consistently doesn't run properly* as suggested by innumerable previous threads, many of which contain discussions about obscure fuel additives, it could have lots of other things that DO cause o-rings to swell up, the most sensible way to eliminate the fuel as a source of problems is to get a commercial fuel of known quality. 

   What does not make sense is to take a known-good part, and then start modifying it, changing materials, to try to "work around" whatever other problem is present, because there is absolutely nothing wrong with the part as it comes from the factory.  That's stacking a kludge on top of an existing problem. Of course, the next step is to "replace the crummy rear needle with a good ST spraybar", which stacks yet another change, now you have to also change the venturi, or the engine suddenly loses 20% of the power, and also induces the potential for more problems with the known "tuning fork effect".

    That's how these things spiral out of control. The fact that a presumably stock part, known to be good, is getting jammed up tells you beyond any reasonable doubt that there is something odd about the fuel, because that's the only thing this o-ring is exposed to that could conceivably cause it. That's a problem that needs to be fixed, forget anything else, before proceeding to the next step, because whatever it is might also be causing the systematic low power and odd run characteristics that Frank has been experiencing, well, forever.

   Of course, as always, it's just advice, no one is compelled to listen or act on it.

   The red flags don't wave any more wildly than this.

     Brett

       No, I am NOT saying that the O-ring expanded when exposed to air. I am saying that is what it is supposed to be sealing against is air leakage. I was looking for a post I thought I made before in this thread but it's not there. I have been working in the maintenance field for 30 some odd years and lots of different applications of O-rings in different environments. Usually what causes an O-ring to swell is something really caustic or some other "hot" chemical like a chemical degreaser or some kind of acid. On some pieces of equipment, it is even desired for the O-ring to swell a bit to help make a complete seal. I have two of these needle valve assemblies from  LA.25's sitting in front of me right now. If everything is working correctly, I don't think the O-ring would ever even SEE fuel. Crank case vacuum should keep fuel flowing AWAY from the area with the O-ring, and the O-ring should just be for ensuring that the threads don't leak air past them. This design didn't work very consistently on earlier OS R/C engines and was often a problem. This design isn't any improvement in my opinion. The fuel comes in the fitting with the barb on it. It turns 90 degrees and goes towards the needle valve and seat, and after it is metered down it turns 90 degrees again and goes to the carb/venturi through the stub that is smooth, no barb. (why do they do that???). I don't like that transition. If the threads are a precise fit, there should be no leakage of air or fuel. If the threads are sloppy, then you get air sucked in and you need some sort of seal up stream, which is the O-ring. The threads on these LA NVAs are pretty coarse compared to what you see elsewhere and pretty short in length. Probably all a matter of keeping production costs down, also known as being cheap to make. I went out to the garage and got two examples of LA.25 plastic back plates with molded on NVAs. One is brand new out of the package.  The other is used, origin unknown, probably came off one I put a metal back plate on and conventional venturi/NVA. The new one, of course, screwed right out. Nice, round O-ring in the square groove that barely offered any resistance. On the used one, guess what!??? It was so stiff I had to use pliers to get it to turn for the first three revolutions or so. When I got it out, the square groove where the O-ring rides is completely filled with swollen O-ring! If I was any good at the photo posting thing I would post a photo , but if some one want to send me a cell phone number or email address I can gladly text a photo or email one. I don't know what fuel this has seen and I'm pretty sure it didn't belong to Frank! This is also NOT the first one I have seen like this. OS has made some pretty good products over the years but in my opinion this NVA is definitely NOT one of them. They didn't work well consistently the first time they came out with them and they still don't. At this point in the discussion, I would venture to say that the O-rings that OS puts in these are pretty crappy. In building and riding vintage dirt bikes, we have to be very careful of what goes through our gas tank and carbs and that means no pump gas with ethanol in it. Neoprene is supposed to be resistant to it but of all the neoprene products I have tried to use I have not found that to be true in either vintage dirt bikes or model airplanes. I would think that methanol would effect things the same way. But my main point is, that the O-ring should not even be SEEING any fuel, if the NVA was designed correctly and built correctly. And I WILL agree that changing to a known commercially made fuel would be a really good test on this. But having said that, there may be some commercially made fuels out there that could do the same thing, depending on what they put in the mix. Testing and time will tell.
  Type at you later,
   Dan McEntee