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Post  dirk gently on Tue Oct 29, 2019 7:53 am

Hello friends!

I just bought this 049 COX engine, and I have a few questions:
1. What is it?
2. Is the 6x4 Thimble Drome prop suitable for this engine?
3. One of the mounting eyelets on the backplate is cracked in the middle. Can I solder it together?

COX QRC restoration (was: Help with identifying an engine) Img_2010


Last edited by dirk gently on Fri Nov 08, 2019 7:12 am; edited 1 time in total
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Post  Marleysky on Tue Oct 29, 2019 10:09 am

Looks like a Cox “QRC” to me. Missing the spring clip that covers the priming hole in the muffler. I don’t think the ear on the backplate can be soldered, but some have used JB weld epoxy with some success.
Here’s the factory instruction sheet from the CEF info files.

https://dbabd7f0-a-62cb3a1a-s-sites.googlegroups.com/site/nitroengine/QRC.pdf?attachauth=ANoY7co5C5N_MKc_vl_masGAxHOz9CIxnhX0cQWI_k1PP_k2keJ5jAFGBviMT-JUzDikBQ-lGQYsbTPcX9Ur7HxjMYvr2GsmTd0zCqOVRBuZtyRpXBnD3ZRjb7_seUEKRiRfsPe71v7bThyNkfmkfWVpKi8i0v4aOjbmN7NtyDBhLyS9jY-qr0RnL8r4qVzDzMKNzM9mGDuHYX6-1Sea_NWtobL2P7qK6g%3D%3D&attredirects=0

Whoa! That’s a long link! lol! probably quicker to click on the links on the LH side of the web page.

The recommended prop size for the engine is 6”x3”.
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Post  Marleysky on Tue Oct 29, 2019 10:21 am

Did a quick search for “backplate fix”. Lots of stuff shows up, but heres the best one from our own Fred:
COX QRC restoration (was: Help with identifying an engine) 499e4e10
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Post  Levent Suberk on Tue Oct 29, 2019 10:59 am

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Post  NEW222 on Tue Oct 29, 2019 4:42 pm

I myself have used JB Weld in the past with success. But, from what you are describing, your 'ear' just has a small crack in it and is not really missing any parts? If so, I would myself, just use it as is. I have a couple engines now that are missing just one ear and run them being only mounted by 3 screws, again with no problems. I do check them often for tightness so as not to seperate from the mount.
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Post  fredvon4 on Tue Oct 29, 2019 4:46 pm

I detest the plastic back plates

over time I bid on and won, or BIN several "lots" of cox engines....most time 10 or more in the $4~$6 per engin range. now have a robust supply of original back plates in the various fill vent configurations

fyi....one ear with a crack will still hold fast if you put a small washer under the screw head

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Post  dirk gently on Wed Oct 30, 2019 7:45 am

Hello,

thank you for your valuable tips.
My mounting "ear" is not missing or fragmented, there's only a crack at the, for lack of better word, apex. This can (barely) be seen in the picture, just next to the end of the exhaust pipe. I will probably just leave it as is, and use a washer I tend to use them anyway, specifically to prevent the "ears" from cracking).

I intend to remove the starter spring "clutch", but leave the spring itself, and use it by engaging with the prop directly.

I take it that "RC" in "QRC" doesn't mean it has a throttle?

On a related note, the engine manual says you can remove extra head gaskets once the engine breks in sufficiently to hold RPM throughout the entire run. Does it mean that if I have an engine that is struggling with keeping constant RPM, a possible solution would be to add an extra gasket? Wouldn't the reduced compression ratio affect the output power?
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Post  Marleysky on Wed Oct 30, 2019 3:48 pm

No, unfortunately the RC in the QRC doesn’t mean Remote Control. I think the Q was to indicate Quiet, because of the added muffler.
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If you remove the starter spring “Clutch” you will need a different starter spring, as the starter spring off the clutch hex drive won’t catch on the prop without the spring extending to the prop. Unless you just bend it.

Yeah, adding head gaskets to a overcompressed (new) engine will lower the compression to obtain a strong steady run.
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Post  dirk gently on Fri Nov 08, 2019 7:23 am

I worked on this engine yesterday. Obviously, it is pretty beat up, but the inside was really worse than the outside.
I opened the engine up to overhaul it, and the tank was almost completely filled with green goop. I'm not kidding, it was a 1/8'' layer of the thing, much worse than the Golden Bee (a.k.a. "Green Bee") I worked on previously. I tried soaking it in petroleum ether, but it made little difference. Finally, and acetone bath and an old toothbrush did the trick.

I replaced the gaskets and the cracked fuel tube, weirdly enough, the reed assembly looked like new, so I left it alone. I removed the spinner, starter string and the muffler for a "no-nonsense" look. I installed a proper (no pun intended) 6x3 prop. I found the glow head was working and the compression was good. The cylinder is a dual-port one.

After reassembling the engine though, I discovered it wouldn't turn freely. Upon further investigation the crank had a lot of resistance and was turning roughly, and the drive plate was pressed against the crankcase, with next to no axial play. I took the drive plate out, cleaned and oiled the parts, and reassembled everything with a bit more play.

After that the engine seems fine and flipping the prop produces the nice "plop" sound we all love so much. I will be test-running this engine in a few days.

COX QRC restoration (was: Help with identifying an engine) Img_2011
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Post  getback on Fri Nov 08, 2019 8:04 am

Looks Good , let us know how she runs i am thinking if it slows down after some running the crank may have to bee removed for some cleaning of the castor build up you spoke of . Huh...
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Post  dirk gently on Fri Nov 08, 2019 8:15 am

I did remove the crank, wasn't really dirty, just dry and lacking oil, and the drive plate was pressed in too tight.
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Post  getback on Fri Nov 08, 2019 8:29 am

Cool i must have misread , most time i do the same if it is in really bad shape . Thumbs Up Happy running !! Beer Cheers
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