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Will TD .049 Carb Body Fit Medallion .049 Crankcase?

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Will TD .049 Carb Body Fit Medallion .049 Crankcase?

Post  GallopingGhostler on Mon Jun 25, 2018 7:50 pm

Can one replace the .049 Medallion carb body with a Tee Dee .049 carb body, venturi and needle valve assembly to the Medallion's crankcase without modification?
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Re: Will TD .049 Carb Body Fit Medallion .049 Crankcase?

Post  MauricioB on Mon Jun 25, 2018 7:58 pm

GallopingGhostler wrote:Can one replace the .049 Medallion carb body with a Tee Dee .049 carb body, venturi and needle valve assembly to the Medallion's crankcase without modification?

YES!! Thumbs Up
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Re: Will TD .049 Carb Body Fit Medallion .049 Crankcase?

Post  GallopingGhostler on Mon Jun 25, 2018 10:34 pm

Thanks, MauricioB.

Next question, will it run under normal suction feed without problems, and will the new Tee Dee venturi set up provide any performance increase over the Medallion venturi set up even if slight?
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Re: Will TD .049 Carb Body Fit Medallion .049 Crankcase?

Post  MauricioB on Mon Jun 25, 2018 10:48 pm

GallopingGhostler wrote:Thanks, MauricioB.

Next question, will it run under normal suction feed without problems, and will the new Tee Dee venturi set up provide any performance increase over the Medallion venturi set up even if slight?

It should not have problems, it has to work well.
You may notice a difference, but it will never become Tee Dee.

As additional information:
I leave here an exploded view of one of my medallion engines.
You will notice that the crankshaft has a round rotary valve opening, while the Tee Dee has a larger rectangular opening.
The cylinders are also different and finally the glow plug of the Dee Dee is of high compression, (different from the medallion of low compression).
All this means that just by changing the pieces that you mention, it is likely that the change (if it exists) is very little appreciable.

Medallion .049:


Tee Dee .049/.051
https://coxengines.ca/cox-.049-.051-tee-dee-crank.html
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Re: Will TD .049 Carb Body Fit Medallion .049 Crankcase?

Post  GallopingGhostler on Mon Jun 25, 2018 11:50 pm

Thanks again, MauricioB. Reason why I asked is that I recently obtained a used Medallion .049 from E-Bay. I have read Peter Chinn's review of the engine. Yes, I would not expect it to perform like a Tee Dee with some improvements, but I see that there is room for improving performance beyond what one can do with a reed valve engine.

Although the crankshaft rotary valve opening is round and not as generous as the Tee Dee, I believe that the free flow of fuel-air mixture is greater than that of the Bees. Bees can be improved by using a Tee Dee cylinder and Tee Dee high compression head.

Would not such be able to enable a Medallion to perform better than stock?

I may want to replace the Medallion carb body, as it is aged a little. For a little more cost over a Mecoa replacement, I thought that an option would be using the Tee Dee one.

First, I'll see how it runs once I clean it up. It will also give me a chance to use my new tachometer I acquired not long ago. Since I have other cylinders and pistons, it will give me a chance to see if we can make this old gal sing a new song.
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Re: Will TD .049 Carb Body Fit Medallion .049 Crankcase?

Post  1/2A Nut on Tue Jun 26, 2018 12:37 am

The TD carb body NV assembly improves air intake as the Medallion has a
NV body right in the flow of the air intake. The fuel atomization dynamics have
changed from one hole in the Medallion NV body to three holes in the venturi.

Next trick to improve rpm is to put a edge on the inside lip of the crank window.
As shown in the pic only on one side per direction of rotation. There many other
mods but this one is simple with a dremel tool and drum wheel grinder or small
round file.

I have a .09 Medallion converted this way and with a high compression
plug boosted the static rpm an additional 1.4k ish rpm as I recall. Also
I used a aluminum carb body which helped extend the cooling capacity
of the crank case. Top end unloaded rpm will naturally increase dramatically.



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Re: Will TD .049 Carb Body Fit Medallion .049 Crankcase?

Post  1/2A Nut on Tue Jun 26, 2018 2:46 am

Here is a run up test of a Medallion .15 with just the venturi mod and
standard glow plug adapter very nice idle with the throttle ring.




AmpAbuser
Uploaded on Jun 16, 2018

New old stock never ran engine brief run up very loud.
15,584 rpm / 27oz thrust / .327hp / 244w / 74 mph PS
I didn't even open the throttle ring all the way, what a beast!
Was left rich for now, need ear plugs to test any further.
25% nitro / 20% oil. Full throttle has the C clip touching
the NV body I only took it open about 60% of the way just
too loud to hold wide open.  


Later I tried a true TD .15 and briefly went full throttle very loud
I was wearing ear plugs for this test.



AmpAbuser
Uploaded on Jun 20, 2018

Cox TD .15 Special
17.9k APC 7x5 / 85 mph / 2.22 lbs. thrust / .495hp / 369.3w
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Re: Will TD .049 Carb Body Fit Medallion .049 Crankcase?

Post  GallopingGhostler on Mon Jul 02, 2018 2:46 pm

Nice, 1/2A Nut Thumbs Up, Amp Abuser's videos are convincing. Verified, there are some things a person can do to improve performance for sport model flying.

The other night I mounted a used prop, shot some motor oil into the cylinder slits and crankcase prop bearing area. The crankshaft was frozen to the crankcase, but with some gentle persuasion rocking the prop it finally broke loose. I put another shot or two of oil, let it sit overnight. That helped, it really loosened up from the congealed Castor. It is missing the glowhead shim washer, I temporarily tightened it with a wrench, has very good compression.

Engine is used, has run time but appears to have considerable life left. It has the original SPI piston-cylinder with one bypass.

The back is on super tight, will not loosen cold. I'll want to do this so I can reset the piston socket joint before test running. The cylinder outside isn't bad, can be cleaned up with Acetone and a toothbrush. The venturi is ultra dusty and dirty, with the oil soaking the outside most the dirt wiped off, starting to look good. It has seen some sun but not enough to bleach the plastic.

This is not bad considering that I paid less than $30 shipping included for a mis-identified engine. More to come .... Smoking





Last edited by GallopingGhostler on Mon Jul 02, 2018 4:58 pm; edited 1 time in total (Reason for editing : Servimg.com problem partially cleared up by posting raw images.)
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Re: Will TD .049 Carb Body Fit Medallion .049 Crankcase?

Post  1/2A Nut on Mon Jul 02, 2018 3:28 pm

Thank you Thumbs Up just a little effort here there goes a long way and it's fun to do!
I like getting the engines all set and ready for a project knowing what's possible power
wise does inspire new planes.

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Re: Will TD .049 Carb Body Fit Medallion .049 Crankcase?

Post  RknRusty on Mon Jul 02, 2018 6:03 pm

Hi George,
The Tee Dee is known for being tricky with hard tanks without pressure. The reason is the TD's 3-hole venturi sprinkler on suction doesn't draw fuel with authority. I believe the venturi on suction tends to feed through a dominant hole and cavitate at the others.  I've only ever run my TDs on a pressure bladder, but with a tank, I suppose cranking and needling may be tricky, as well as loops and hi-gee maneuvers.  

That being said, I see no reason not to try it if you have a spare TD intake assembly. I'd like to know for sure if what I'm thinking is right. Btw, the crankcases are the same in every way. I usually use a small square needle file to flatten the rounded bottoms of the backplate's wrench-slots. That provides better grip so the Cox wrench doesn't cam out and scar the backplate up. Warm it with a heat gun to help free it up too. Sometimes I use the long edge of the wrench, rather that the toothed claw end.
Rusty

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