COX 049 PT 19 product engine and Sure Start testing

as Balogh said above the surestart really needs the fuel tube over the needle to seal it! they vibrate and leak like a sieve!

I do mine a little bit different to Balogh I think. I actually remove the black NVB seal, then I get some really tight fuel tubing and put over the needle. I cut the tubing such that A small washer sits against the little shoulder on the needle and the tube below it. Then as you pt the needle into the NVB/spray bar the tube will cover the spray bar top and the washer will stop the tube moving up the needle. If you cut it to the right length this then provides the tension the spring on the needle would have provided as the tube compresses and stops the needle turning and leaking. The trick is assembling it with a grey horseshoe backplate. Push the needle through the round top bit of the backplate then before it goes very far, using tweasers or pointy nose pliers put the small washer on the needle, then the fuel tubing them push the needle into the spray bar without it all falling apart. Lol.

Anyway whichever way or how you do it, you absolutely need the fuel tubing on an 049 surestart to seal the needle or the thing will run all over the place. even putting side pressure or down pressure on the needle will change the way its running. The fuel tubing definitely fixes the problem, then they run great!

Yabby

Thanks for the heads up about the thin alley shim material, hadn't thought of that. Thanks.

And the fuel tubing and washer trick. I have used fuel tubing before on a magnum gp40 needle before when the "sprung clip" broke in half. Usefull stuff and info.

Yabby I do the same thing with the washer on the NV

Excellent Photo Bologh! Describes it perfectly, Says soo much more than my mixed up words Lol.

Yabby

Thanx for the tips, András ,Coxfledgling and Yabby,
Will do this on Sure Start and report the test run results,
RGDS

May I ask please, how effective is the RC operated exhaust restricting sleeve ?

I suppose it all depends on fit etc. but if the sleeve blocks the exhaust ports, the engine will stop ?

This what I would like to happen, an RC control of engine speed and a means of cutting the engine in flight if needed ( loss of control due to pilot rather than radio signal problems ).

In general the stock exhaust throttles sold by Bernie and Matt for the stepped and thick wall cylinders are quite handy, but they will not fully stop the engine, just idle it to a few thousand rpm-s. This may allow a low speed landing with a large prop and midsized- not small - plane powered by a 049 COX engine.

The one on my photo was made by me for a thin wall old stock cylinder that has a flange at its bottom, not allowing the use of the standard exhaust throttle. I made that by winding a strip of repurposed beer can aluminum strip around the cylinder, slit it diagonally opposed where the exhaust openings are, and hold it tight with circlips, whose eye accommodates the pushrod end for RC control. It's efficiency depends on how accurately you wind the coil around the cylinder. Some I made are very good, others are less.

This one I made for a TeeDee051 seals and idles as well as the stock.



The one on my red postage stamp backplate reedie is a bit mediocre but still good.

I really like the design of that exhaust throttle you made Balogh I think if I put in the time and effort I could make one fit and work fairly well inside of the standard cox round muffler. I need a muffler on my engines where I fly. I can get the throttle Bernie has for grey backplates for my surestart engines, but the exhaust throttle on a TD I would have to make work with the standard Muffler as the TD is much noisier that a Surestart to begin with. And the RC carbys for TDs are out of stock, and looking at them I dont think they would fit with a muffler anyway. So your beercan and circlip design.... might be the go for me to integrate into a muffler on a TD, as Im buying a cheap RC Tx and Rx to play with. My lad wants to have a go. Im going to make some hacky flat platforms with wheels and using the engine and a prop and the rx etc mounted on it with servos and stuff to get used to the Tx/Rx, electronics, how it works and stuff, as that is much easier than wrecking planes in the process. :-)

Yabby

Thanks, Yabby.

The muffler and RC carb can fit when mounted on a TeeDee together. This is a Tarnot Carb but its dimensions are the same as the COX RC carb.



If you want to combine my makeshift exhaust throttle with the muffler, take note of the narrow clearance between the cylinder neck and muffler.

I am looking forward to seeing your solution!

Ive been looking at my TD 049 and am thinking of not using exhaust throttle, I dont particularly like exhaust throttles, they are not a throttle but a means of applying back pressure that constrains the engine and holds in heat. Maybe thats not really a problem as lots of people use them and have no problem.

I have two ideas for doing it. I have ordered two 049 grey backplate throttles from Bernie and Im thinking of hacking one to fit on my TD venturi. The other idea is two flat plates of aluminium. 1 with a hole just smaller that the top of the venturi, slide that plate up the venturi and fix in place. Then the second plate is pinned or hinged to the first plate and connected to a servo such that it slides across the carby mouth. I think this is the best solution and the simplest and I reckon I can do it and have my round cox muffler and my spring starter as well.

Time will tell! I will let you know how it goes. If it works I will post the design. should be simple but not easy to make maybe. Lol.

Yabby

An old trick we used on plastic back plate 290 and later engines was to back out the needle valve until it had only one or two threads holding it in place and then smear PTFE plumbers thread sealant on the needle valve threads and screw the needle valve back in. Works great and the fuel does not dissolve the sealant.

The earlier postage stamp 290 NVB had a slit in the exposed part of the threads that supposedly was crimped slightly to make the threads grab the needle valve and make it not so loose, but they leaked anyway. Cox quit cutting that slit and instead used a hard plastic seal pressed onto the end on the NVB, which worked. If the Needle valve gets loose, it is a simple matter to replace the seal, and use a little PTFE if needed.

I just remove the black seal, heat it with a hair dryer and crimp it's end with a cable crimper where it accommodates the threaded NV..will grab the NV and prevent vibration...plus pull a fuel tube on the seal and NV both as in my photo a few posts up..

I keep meaning to ask Balogh every time I see his photo .....what is the black plastic item in fuel line appearing to attach to the NV?

Fred that is a fuel stopper tucked into the filling line of my balloon tank. It came with an eye at its outside end that can be tied with a tread to the fuselage so that it should not be lost while fuelling, and  hooked on e.g. the NV knob so that it should not dangle mid-air



That dented green deflector was cut from a Heineken beer can (an encounter of 2 addictions ), and fixed behind the engine mount to protect the Oracover on the firewall from the excessive exhaust heat

Some really good ideas and explanations there! very helpful to me. I had often wondered about some sort of gunk on the needle to help seal and prevent vibration but I only have a few of the rounded NVBs for my TDs and dont want to risk them as cant get them any more. On my TDs I use a rubber band around the NV and the NV Leaf spring and have found it stops vibration and stops it moving on its won. So far they havent leaked, but if they do eventually I will try tubing, new NV as can still get them, and if needed due to the wear being in the NVB I will try putting gunk on the NV thread, but so far so good. On my surestart engines I always use fuel tube on the NV!

I like the engine mount Balogh :-) The photo gives a great perspective of size and fit. Lucky you happen to have access to the odd beer cans, they are essential to the design and build.

Yabby

Thanks, Yabby..this is a very old 051 with thin wall cylinder - hence the DIY throttle ring on it.

Thank you makes more sense now
sorry if I missed this in another thread