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Post  layback209 Mon Mar 21, 2022 1:10 pm

Hi Everyone, almost have a fun little project wrapped up. Thought I'd share.  

Here's repair list;
missing the bushings for the helicopter blade main axle assembly.  
engine back plate had a crack through the venturi opening, needed ball and socket reset
engine gummed and had wd40 or something nasty sparyed in it.

I made new split bushing from a wood dowel. I made a fixture that I could us in the drill press then turn the dowel down to the correct diameter.  Once to dimension, I inserted a razer blade in the drill chuck and sliced the dowel bushing in half. Worked amazingly.  Same approach for the spacer. Wood glued and held on with heat shrink tubing.

Now the saucer body is good to go.  Ultrasonic cleaned the engine.  Rest ball socket. Now to decide which backplate style to use. I have the classic horse shoe or the one with the choke.  Then all that's left is bolt er up and go fly it with the kids Very Happy Babe Bee .049

Flying Saucer Repairs - "Gravity Resistant Flying Machine" 20220312
Flying Saucer Repairs - "Gravity Resistant Flying Machine" 20220310
Flying Saucer Repairs - "Gravity Resistant Flying Machine" 20220311


Last edited by layback209 on Mon Mar 21, 2022 3:08 pm; edited 2 times in total
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Post  layback209 Mon Mar 21, 2022 1:11 pm

Flying Saucer Repairs - "Gravity Resistant Flying Machine" 20220313
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Post  rsv1cox Mon Mar 21, 2022 3:01 pm

Good job. I like it.

And "engine gummed with WD40." Yes, nasty stuff. It never gets near any of my engines.
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Post  layback209 Mon Mar 21, 2022 11:08 pm

Thanks, got it all together and ready to test. So turns out every one of those choke style back plates is cracked where the spray bar is inserted. Even the 2 new ones I bought from cox international were cracked. Huh... So I motosealed it all together, hope for the best. If it works it works. From now on its only non chock style backplate. Engine has amazing compression. 2 head shims installed. Probably needs more run in.

Hope to have a flight report soon.

Flying Saucer Repairs - "Gravity Resistant Flying Machine" 20220314


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Post  GallopingGhostler Tue Mar 22, 2022 12:22 am

The original "290" engines, the "postage stamp" back (engines and replacements for the RTF's) were molded out of DuPont Delrin, which was almost indestructible. My 290's from the early 1970's are as good now as they were then, IMO. It appears that the earlier horseshoe backs were also made of the same material. The latest plastic of the horseshoe backs is of a different plastic, appears brittle. Since the stocks could be as old as 25 years, it is possible that the plastic became age hardened. I attempted to remove the NVA to repair a Testors McCoy Rotomatic engine from a new horseshoe back I bought a couple years ago, and it cracked.

(A common practice before was to remove the NVA and drill out the venturi to allow more air to pass, increasing the engine's power. With the back cracking would make this maneuver impractical.)

Seems that since this is a common occurrence, may be if someone in the community could make either a metal or plastic collar band that would wedge the crack shut and hold it firm, (say 0.001" undersized for tight fit) might be a good way. I don't know if the choke tube is sufficient along with cracked edge sealed with sealant to help salvage the situation.
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Post  davidll1984 Tue Mar 22, 2022 6:14 am

Someone here already fixed this crack in the horseshoe backplate using a coper tube or aluminium one Not sure cant rember Huh... cool flying saucer i never se one of those Babe Bee .049
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Post  getback Tue Mar 22, 2022 8:00 am

Cool deal I like the way you made your own bushing and spacers to fit , Good luck on the flights with the Kids!! Babe Bee .049
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Post  layback209 Tue Mar 22, 2022 10:34 am

I like the idea of the tube/ring to close the cracks. Thanks. I remember reading about that on here for TD venturi bodies. I gotta get that old metal lathe going Doh! This Site Rocks! to bad about the quality issues over the years.

See if the janky fix will holds up enough, my goal was to seal the airleaks. The choke does cover the venturi nicely. Now thinking about how that engine will be freewheeling around the tank will probably apply a load the spray bar, cracked area. I do have a non choke backplate I can bolt on, might be a good idea to bring it to the field.

Here's the fixture I came up with to hold the dowel bushing for "machining." I new there was no chance I could drill the hole dead center. So I drilled the hole first, incerted the fixture with a drop of ca. Then held the rod with the drill press chuck to turn it. That way I could use a file and square off the drill press table to "true" it up, file to dimensions. According to my caliper I got it with in .1 mm Very Happy good enough.

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Post  NEW222 Tue Mar 22, 2022 6:00 pm

If you wanted or needed actual dimensions of the missing bearing, I can get those for you off of my UFO.
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Post  layback209 Sun Mar 27, 2022 5:26 pm

Flew the saucer today! It was a big hit with the kids. Had a few issues starting it, no fuel draw. Put it to the side for a bit then tried again and it was good to go. My guess is the read was sticking a bit or something.

It's so darn cool. It even sounds like a alien ufo. And kinda hovers around. This model needed to be run at near peak to fly properly, I thought wet 2 cycle would be good but not enough. Fun morning and all. Lots of flights, the engine should be near broken in now, and looks like my janky fix is working so far.

Thanks NEW222 appreciate the offer. Illreach out if I need to make some more.
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Post  Levent Suberk Mon Mar 28, 2022 5:51 am

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Post  getback Mon Mar 28, 2022 7:04 am

Cool Man I bet the kids were all in to it Very Happy , Never seen one but seem to bee cool for the time period .
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Post  Levent Suberk Mon Mar 28, 2022 8:11 am

To fix cracked venturi you can try different round ballpoint pen barrels for a snug fit on venturi. A piece of ballpoint pen barrel is enough to fix it. Sanding inside of pen barrel piece with rolled sandpaper can bring it to snug fit size. I didn't try yet, but I think that it works.
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Post  GallopingGhostler Mon Mar 28, 2022 2:37 pm

Levent Suberk wrote:Surestart backplate fix:

https://www.coxengineforum.com/t14591-surestart-engines-with-cracked-backplate-housings?highlight=Surestart+crack

MauricioB wrote:I have seen that problem on gray plates. Therefore a while ago I made this solution. You can even make it long and also place an air valve if it is of your interest. The aluminum alloy tube is the permanent and definitive solution to this problem that comes from the source.
Flying Saucer Repairs - "Gravity Resistant Flying Machine" 20201016

Flying Saucer Repairs - "Gravity Resistant Flying Machine" 20201017

and if you want you can place an additional air valve RC Plane
Flying Saucer Repairs - "Gravity Resistant Flying Machine" 20201020

Mauricio came up with a deluxe fix, plus enhanced it with a choke style throttle. Back in the mid 1970's, I worked a year in the shop of Research Corp. of the University of Hawaii's Geophysics Department. As a student help at minimum wage (cheap student labor), I helped Bert, a german immigrant watch maker, who as their machinist made parts for the UH Geo's ocean bottom seismometer project, having access to very nice Bridgeport milling machines and lathes under Bert's helpful eyes. Then they found I could do electronics, soldered components onto custom printed circuit boards for the seismometer instrumentation package.

A bit of a pragmatic practical realist  Old Bugger , at this later stage in retirement, affording a $500 miniature modeling lathe/mill might be quite a stretch to repair a $7 engine from the Cox Surplus Sales outlet (April 12, 2008).

Flying Saucer Repairs - "Gravity Resistant Flying Machine" 2008-010

But again, I am flabbergasted Wink by the excellent workmanship done by Cox Engine Forum craftsmen. Smoking

Levent Suberk wrote:To fix cracked venturi you can try different round ballpoint pen barrels for a snug fit on venturi. A piece of ballpoint pen barrel is enough to fix it. Sanding inside of pen barrel piece with rolled sandpaper can bring it to snug fit size. I didn't try yet, but I think that it works.

Levent, that is a good bit of practical thinking on an inexpensive solution to the gray horseshoe cracked venturi problem. Thumbs Up

Brainstorming (a lost art these days  Surprised ), I do wonder though if a ball pen plastic, probably the least expensive in the world would be be able to stand up to the high frequency vibrations and residual temperatures of a Cox .049. My initial thoughts are probably using "right sized" available aluminum or copper tubing, with gentle round filing to snug fit and a touch of Epoxy glue to lock into place. Tired w/ Coffee Read
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Post  Levent Suberk Mon Mar 28, 2022 4:41 pm

Ballpoint pen handles are made from polystyrene or polypropylene as like as Bic ballpoint pens. Because they are seamless they are very resistant to crack. Aluminum is better perhaps. Need to try Very Happy
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Post  layback209 Mon Mar 28, 2022 7:52 pm

Wow there is some excellent repairs done on this issue. This Site Rocks!

I reached out to Cox International to see if they have any good backplate left. If not may try one of these fixes if the engine acts up.

Here's the crew from Sunday Funday. All 3 generations were out.

Flying Saucer Repairs - "Gravity Resistant Flying Machine" Img_4710
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