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Old Cox 049 will not hold RPM

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Old Cox 049 will not hold RPM

Post  Back to CL on Tue Apr 24, 2018 1:17 pm

Hello everyone, My first post here but have learnt a lot with your discussion threads.

Have this old Cox 049 that i refurbished. Starts in one spring turn. Often roars to 18k RPM . But does not hold the RPM, will slow to 11k and back to 18k. Have a new spring on the needle valve, hoping it will help. Fuel is OK as my new Babe bee runs very smooth.
Suggestions and help please. Not sure what to do. Have run the engine about 6 tanks full. It runs till the tank empties.
By the way, this old classy trainer that I have had for a decade. Flies well to retrain me. What airplane is this. I have no recollection.
Thanks in advance,

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Re: Old Cox 049 will not hold RPM

Post  Cribbs74 on Tue Apr 24, 2018 1:36 pm

Remove the NV, install small washer, piece of fuel tubing and omit the spring.

If that doesn’t fix it, you have a tank leak. Backplate screws, tank to venturi and backplate to tank are all leak sources.
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Re: Old Cox 049 will not hold RPM

Post  Ken Cook on Tue Apr 24, 2018 2:42 pm

Assuming all that Ron mentioned is in order, and your certain the reed is working correctly I would look at the crank. If that engine has been sitting for a long period, it's quite possible that the castor goo has engulfed the shaft. The engine goes up in rpm's, then the goo heats up a bit and actually grabs the shaft and slows it down. It won't flush itself out and must be manually removed by removing the splined drive washer on the nose.
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RE: Old Cox .049 will not hold RPM

Post  66 Malibu on Tue Apr 24, 2018 5:27 pm

The airplane you have is called the Delta Dart II Amazer put out by Midwest.
It is a bare bones trainer kit for first time C/L flyers that is pretty unique.
The youngster builds it himself almost like a scout project pinewood derby racer.
There is a duckbill balsa attachment that mounts where the engine goes so the first timer can "whip" the plane around with a 36" long 3/8 inch dowel attached the bell crank.
Once totally comfortable with spinning around and controlling ups and downs then the duckbill is removed and the plastic engine mount you have and engine are attached.
Add the control handle and the fun begins.
I guess the kits were sold to groups like Boy Scouts to introduce the hobby to new people.
I scored two such kits off eBay about 10 years ago for $14 each shipped.
Have never seen any show up since....
FWIW......Steve...
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Re: Old Cox 049 will not hold RPM

Post  RknRusty on Tue Apr 24, 2018 9:18 pm

Good grief! There really is such a thing. I was going to answer that it's probably just a buncha' wood scraps someone turned into a plane, Lol. It looks like the perfect thing to re-train with. Plenty of wing and stab, and easy to fix in the field. Welcome to the forums.

Also, about the engine; the narrow venturi tube that extends from the tank and fits into the breather inlet in the backplate has a small round flat washer around its tip that can be easily lost, overlooked, or mistaken for crud. Some people use small o-rings in place of it, but be careful not to distort the backplate when tightening the 4 screws. A leak there will make the engine unruly, especially when the fuel level drops enough to uncover it.

I would definitely recommend following Ken's advice, disassemble and clean the internals before pulling your har out chasing phantom air leaks. I use lint free rags and 10 weight oil when rebuilding. Singer sewing machine oil at Walmart or most any craft store, or air tool oil is perfect for the job. They are probably both the same thing. It's clear oil with little or no solids or wax in it to gum up later.

It can be difficult hunting down air leaks on the engines with built-in tanks. You may be asking more questions as you rule out possibilities, so we'll help you knock it out, one thing at a time. And there are a gazillion threads about the same problem you are having, but don't let that stop you from asking. Parts can be found at www.coxengines.ca (that's Bernie). And also at www.exmodelengines.com (that's Matt).

Good luck,
Rusty

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Re: Old Cox 049 will not hold RPM

Post  roddie on Wed Apr 25, 2018 9:32 am

Back to CL wrote:

By the way, this old classy trainer that I have had for a decade. Flies well to retrain me. What airplane is this. I have no recollection.
Thanks in advance,




When "Steve" (66 Malibu) identified your model as the "Amazer" and described its functionality.. I knew that I had info on it somewhere. I had photocopied a few pages of a Dick Sarpolus book; "Building and Flying Control Line Model Aircraft"



Pages 52 and 53 contain some information on the model;





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RE:Old Cox .049 will not hold rpm

Post  66 Malibu on Wed Apr 25, 2018 5:34 pm

Thanks Roddie and Marleysky for the research and intel work you guys presented.
The more you know about something is always good.
I had bought those two kits off eBay to get two grandkids into the hobby.
Right after that I got a newly built Sig Dewey Bird with a new Baby Bee for about $25 and a jackpot deal on a newly built Sig Sky Ray, new metal back Black Widow, lines and handle, and a new Cox starter kit with fuel for $10 at the Perry swap meet !!!!!! Seriously, at the last table before going home, I saw the Sky Ray and the guy said you're the only guy to even look at it ,so you can have the whole works for $10 !!!!!! Bingo !!!!
Because of the two Sig planes, saw no need to build the Amazers.
I kind of the keep them as a reminder of what I missed all those years that I had bust it working!! HA !!
Thanks again...............
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Re: Old Cox 049 will not hold RPM

Post  1/2A Nut on Thu Apr 26, 2018 2:41 am

How much castor is in the fuel? Another possible issue is it is heating up then sagging.
Needs to stay cool you are certainly not over propped. The engine looks to be in good shape.

For sure check that the tank screws have not come loose and do the NV trick before taking a engine apart.
If you did a full take down and rebuild you would have seen the old castor build up on the crank.
Sometime refurbish is a few parts bought and a external clean up which maybe your case.


Best fuel for that engine is 18 to 20% castor and 25% nitro.
You need to buy 1/2A fuel really no other fuel blend is worth messing
with. 1/2A fuel always has a majority of castor no less than 14% ever
with that low percentage always good to add some synthetic at least 3%
to help reduce varnish build up. Never exceed 24% oil package as it becomes
a unnecessary load on the engine.
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Re: Old Cox 049 will not hold RPM

Post  Back to CL on Thu Apr 26, 2018 10:34 am

Thank you everyone for your support. Thanks for all the research on the airplane. I am just getting back to CL so am using this small Amazer to get rid of dizziness before I go to 1/2A Sig Skyray.

I am using fuel that has : Contains 25% Nitromethane, 55% Methanol,10% Synthetic Oil,10% Castor Oil. A regular 1/2A fuel only. Same bottle of fuel and my Cox Babe bee runs great, no issues.

Will re insert the screws at the back plate and can an JB Weld Drop at the end of the screw help stop the leak for further assurance? Or a drop of silicone latex? Will remove the NV and insert a small washer. Do you anyone of you have a photo of how the washer goes in instead of the spring? Jest plot it down?

Thanks again for all your support.
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RE:Old Cox .049 will not hold rpm

Post  66 Malibu on Thu Apr 26, 2018 11:48 am

FWIW....
Before you attach the tank look at the back of the crankcase where the screw holes were drilled and tapped.
There will be ( about 100% chance) small burrs around the holes.
Lay a piece of 600 grit emery paper on a flat surface, add a drop of machine oil, and rub the back of the crankcase in a figure eight pattern a few times.
You can see and feel if the burrs are gone and then clean it up.
I would not use JB Weld on the screw tops to keep them in place. It is a bear to remove when you have to reset the rod and piston later.
I use a drop of silicone on each screw head.
On the needle valve you will need a small piece of fuel line to slip on after you put the #2 washer on first.
The fuel line becomes the seal and spring..
That's the way that seems to work best...
YMMV.....Steve.
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Re: Old Cox 049 will not hold RPM

Post  Back to CL on Thu Apr 26, 2018 2:41 pm

Hi Steve,

Will do the Emery board process to deburr.
Regarding the fuel tube above the #2 washer. Same length as the spring I assume?
Sorry for asking such newbie questions, but much appreciated. Thanks
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Re: Old Cox 049 will not hold RPM

Post  Cribbs74 on Thu Apr 26, 2018 3:13 pm


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RE: Old Cox .049 will not hold RPM

Post  66 Malibu on Thu Apr 26, 2018 3:25 pm

Be careful with the emery board in that it might lower part of the crankcase mating surface.....
Then you will have sure nuff vacuum leaks and a real bad run.
Cut the fuel tube about the same length or a little longer for a better seal.
Put the washer on the needle valve first and it will stop at the flange on the needle valve.
That flange was the spring keeper to maintain pressure to keep the needle valve from rotating when the engine is running. The washer is the retainer for the fuel tube.
Once you put the fuel tube on the needle valve carefully screw the needle valve clockwise until it stops turning.
Then trial and error turn counter clock wise about 2 turns to begin tuning when the engine starts.
Treat those parts as a jeweler not as a blacksmith and it all should work well.....
Steve............
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Re: Old Cox 049 will not hold RPM

Post  Ken Cook on Thu Apr 26, 2018 7:57 pm

Ron, is that a new production tank from Bernie?
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