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Engine help near Lancaster PA

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Help! Engine help near Lancaster PA

Post  AmishPilot on Sat Jul 09, 2016 3:05 pm

Hey all,

The control line piper Comanche model I got for my dad for Father's Day is finally assembled. We started the engine once successfully and ran a tank through quite rich (for break-in)! However, upon trying to start it again we found that once we finally manage to get it to run, if we don't keep a finger on the needle valve, it shakes so much that it vibrates and turns erratically to the point that it chokes itself out one way or the other. Do you have any tips on this? And more ideally, is there by some miracle someone nearby Lancaster PA who would be willing to meet up and help us out and get this old beauty out for a maiden voyage?

Thanks in advance for any tips!
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Help! Re: Engine help near Lancaster PA

Post  Marleysky on Sat Jul 09, 2016 4:07 pm

Glad you got the bellcrank assembled correctly. Go to  page 40 of those same instructions.  There is a picture of the engine and needle valve. The needle valve should have a little spring on it between the Venturi body and the needle valve. The tension ( from the spring) should keep the needle from turning while the engine runs. If it does not have the spring you may be able to substitute a short piece of fuel tubing to act as a "air seal" and provide the friction to keep the needle in position.
Check out the pictures here:
https://www.coxengineforum.com/t5250-needle-valve-screw-don-t-stay-put?highlight=Needle


Last edited by Marleysky on Sat Jul 09, 2016 4:16 pm; edited 1 time in total (Reason for editing : Pictures)
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Help! Re: Engine help near Lancaster PA

Post  Ken Cook on Sat Jul 09, 2016 4:36 pm

I wish I could assist, my time frame hasn't allowed for hardly any flying. I might suggest the H.A.M.S club in Harrisburg, PA. Harrisburg Aeromodelling Society. I would think doing a search would reveal some contact info. I would think that's not real far from your location. Ken
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Help! Re: Engine help near Lancaster PA

Post  roddie on Sat Jul 09, 2016 5:56 pm

Good advice from "Marleysky"! There's plenty of ways to "temporarily" solve your issue with the needle vibrating and turning. Try a strip-piece of thin plastic.. (like the transparent plastic used for packaging items on peg-hooks at the store..) Cut a piece about 1/2" x 2" with scissors.. and cut an open slot (1/2" long) into one end, to capture the needle-valve stem (like a fork). Cut the width of the slot slightly thinner than the diameter of the needle valve shaft for a "friction-fit". Tape or rubber-band the plastic strip to/around the fuselage. This should hold the needle-setting for a few flights.. until you can source a more permanent and aesthetically-pleasing/functional means to keep the needle from turning. A "Bobby-Pin" (woman's hairpin) might even work with some rubber-bands holding it on around the nose of the fuse.





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Help! Re: Engine help near Lancaster PA

Post  GallopingGhostler on Sat Jul 09, 2016 6:21 pm

Depending on the version of engine, Cox International has needle valve springs, for example:

http://coxengines.ca/cox-.049-.074-needle-valve-spring-3.html



So does Ex Engines:

http://www.exmodelengines.com/cox-.049-needle-spring-3.html



Not saying those are the ones you need, but they have others.

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Help! Re: Engine help near Lancaster PA

Post  Cribbs74 on Sat Jul 09, 2016 7:23 pm

Usually when the needle turns on it's own is because the little rubber piece is dried out. The spring does help, but that piece of tubing also keeps air from leaking past the needle.
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Help! Re: Engine help near Lancaster PA

Post  GallopingGhostler on Sat Jul 09, 2016 7:46 pm

I've done both. Not familiar with what specific version of engine came with that particular Cox RTF. Seems to be an as case basis. Worst needle set up with the OK Cub .049's I've got. They have a sleeve over the needle valve assemble that has a slit on both sides with a tapered blunt tip needle. I put a section of small silicon fuel line that covered the slit and spray bar, which helped, but still needle was a bit touchy for my comfort. I'm sure he'll get it sorted out.

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Help! Re: Engine help near Lancaster PA

Post  gcb on Sat Jul 09, 2016 8:47 pm

GallopingGhostler wrote: ...Worst needle set up with the OK Cub .049's I've got. They have a sleeve over the needle valve assemble that has a slit on both sides with a tapered blunt tip needle. I put a section of small silicon fuel line that covered the slit and spray bar, which helped, but still needle was a bit touchy for my comfort. I'm sure he'll get it sorted out.


George,
Many OK needles only have a blunt end that provides a slobbering rich to full lean in less than a turn. For these I file (or sand) some taper on about 3/8" to 1/2" of the needle.

George
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Help! Re: Engine help near Lancaster PA

Post  GallopingGhostler on Sat Jul 09, 2016 9:03 pm

Fit and finish on the Cub wasn't that great, needle had a little wobble to it, which didn't help. A simple wiggle would cause mixture to change drastically. I haven't tried the filing fix yet, George. I'm almost tempted to JB Weld a Cox NVA to one.

Given the quality control issues, I'd understand why Cox surely dominated the market. Every new Cox reed valve engine I purchased ran right out of the box, and ran good until I crashed. Wash the dirt off, clean back screen. After a season of running, devarnish the cylinder, back in business.

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Help! Re: Engine help near Lancaster PA

Post  Oldenginerod on Sat Jul 09, 2016 10:38 pm

Cribbs74 wrote:Usually when the needle turns on it's own is because the little rubber piece is dried out. The spring does help, but that piece of tubing also keeps air from leaking past the needle.

Cox International has these-

That's fine if using a non-tanked backplate.  The tanked version has no seal, but as already mentioned, you can use a small piece if fuel tubing to seal the needle.
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Help! Thanks for the help

Post  AmishPilot on Tue Jul 12, 2016 10:55 am

Thanks for all the help and ideas, folks! After some fine tuning we were able to get the engine running reliably. Also, since this is the older style model with a fuselage held together with rubber bands, we simply ran a rubber band around the needle valve. It naturally ran right beside the valve so there shouldn't be an over abundance of torque on the needle valve I shouldn't think. Maiden voyage scheduled for today!
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Help! Re: Engine help near Lancaster PA

Post  fredvon4 on Tue Jul 12, 2016 11:57 am

On the Tanked Cox engines I find it useful to first put on a well fitting flat (usually #2) washer, then cut the fuel tubing to just a hair longer then the normal running setting so there is a slight compression of the tubing... no washer and the tubing does not seal and also vibrates up the Needle to the knob

For the non tanked, the hard rubber items shown above, are the ticket... they are NOT threaded so the first use demands some effort to fully seat the needle...caution!!!! this first use is very hard and "feeling" the needle bottoming out is hard to detect

If you go too far you WILL damage the needle and it seat

Before I do this I take the loose needle and get it started withOUT the new hard rubber piece...., and carefully COUNT the turns in to fully seated...then install the new holder/seal and stay one full turn less than fully seated..... ( hint the typical running setting is 2.5 to 3.5 turns OUT)

These dinky engines are finicky...don't create problems... as Rusty has posted about a hundred times...CLEAN/CLEAN/CLEAN and then if not sure clean AGAIN!
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