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Post  Iceberg on Thu Nov 15, 2018 4:30 am

Hi Friends
I have a couple of .049 Medallions. They were not in pristine condition but reasonable. I'm having some success with one and the other less success. The one with less success had the wrong needle. It seems to have too much fuel going through. But the the part that really is stumping me is that it will run backwards for 10 seconds or so then quickly change direction at fast speed and then conk out. More fuel just floods it. Occasionally i'll get it to fire and it fires fast for a minute or so then stops. But why running in reverse? Does the piston need to be higher with a shim or something to alter the timing? My Tee Dees occasional y run a smidge in reverse but not like this one. I already cleaned all inside and used a needle from an old sandblaster that the threads fit nicely. I know that the proper factory needles and new spray bar would help but running in reverse?

Thanks!!
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Post  Ken Cook on Thu Nov 15, 2018 4:32 am

A engine with too much prime will run backwards. That's a problem I'm faced with currently here at home. The temps are in the low 40's and upper 30's requiring much more prime to get them started. When they do start, they run backwards. Sometimes you can pinch the fuel line off and let the engine run backwards and right before it quits, it pops and runs forward in which you release the fuel line.
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Post  Iceberg on Thu Nov 15, 2018 4:52 am

Thanks Ken. But I'm staying indoor 70 plus degrees?
Thanks
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Post  Surfer_kris on Thu Nov 15, 2018 6:32 am

The Medallion has a milder timing on the intake than the TD, and therefore the Medallion will run "better" than the TD will in reverse.

The easiest "fix" is to use a spring starter, and to prime a little less. That what you get a faster flick of the prop and they tend to start and run in the right direction.
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Post  Iceberg on Thu Nov 15, 2018 7:00 am

Spring starter am option but it's there a timing option even though the Medallion ruining is softer than tee dee?
Thanks
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Post  balogh on Thu Nov 15, 2018 8:32 am

I think the milder timing Kris refers to is defined by the small OD circular opening on the crankshaft, also located to open a bit later for fuel/air entry into the crankcase than with the larger rectangular opening on a TeeDee shaft...the shims placed under the cylinder will not change the intake timing in my opinion
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Post  Levent Suberk on Thu Nov 15, 2018 8:58 am

As Kris mentioned use a spring starter or an electric starter.

Although you can make an electric starter, you also can buy it:

https://coxengines.ca/sullivan-hornet-1-2a-electric-starter.html

Avoid using electric starters with flooded engines because electric starter can bent crank pin.
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Post  GallopingGhostler on Thu Nov 15, 2018 11:29 am

Surfer_kris wrote:The Medallion has a milder timing on the intake than the TD, and therefore the Medallion will run "better" than the TD will in reverse.

Ron Cribbs uses an .049 Medallion in his Baby Clown, was amazed how well it flew, just like the larger ones. Am told Medallion has better fuel suction feed than the Tee Dee, which works well for CL stunt.
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Post  Surfer_kris on Thu Nov 15, 2018 12:11 pm

Yes, for many people and applications the Medallion will work better than a TD engine. The TD is really designed for all out power, while the Medallion is designed around reliability and user friendliness. So it is designed to have a milder timing and a better fuel draw etc.

The intake timing is controlled by the window in the crank combined with the intake opening in the crankcase. The medallions have a small circular crank opening wile the TD has a rectangular opening. There is no easy way of changing the intake timing, and there is no reson to either. The medallion running backwards is not a deign error in anyway, it is just how an engine will and should behave.
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Post  Iceberg on Thu Nov 15, 2018 3:33 pm

Thanks for all the comments. I have obtained two second hand Medallions and they also have slightly different venturis one has the stud to catch the sprng starter the other does not. One has a nut socket for the spray bar the other has nut socket on both sides. One came with the right needle but bent. The other one had the wrong needle from a .020 I think. Needless to say they were mixed and matched. I need to upgrade the venturis and the needles. Since I'm over here posted in Korea will need to somehow get those. Appreciate all the comments.
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Post  Ken Cook on Thu Nov 15, 2018 4:09 pm

If you over prime or flood a engine it will run backwards. I made the cold comment because that's what has happened to me numerous times this month. When it gets cold, it's extremely easy to over prime and yes they run backwards. A TD does it and so does a Medallion. They don't run well, but they can run backwards
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Post  944_Jim on Thu Nov 15, 2018 5:48 pm

I love my Hornet starter.
I usually splash a bit of fuel between the prop drive plate and the crankcase on my .061 APs and .074 Norvels. Now that they are broken in, they finger-start pretty easily.
The Cox engines get the finger.

Oh, and the one that runs backwards...maybe it really has a reverse crankshaft? I understand that was an available crank. You may be able to check timing between both cranks. Remove the backplates, gently insert a paperclip down each Venturi to lock each crank to one side (the same side of the crankcase, say to the left), and then check the conrod pins (journals) to see if they are "clocked" the same.
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Post  Dave P. on Thu Nov 15, 2018 7:13 pm

Hi there Iceberg.  I recently scored several Medallions in various states  of disrepair.  I managed to find all the parts you mentioned.  Mecoa has the venturis.  Between Matt at EX Model Engines and Bernie at Cox International you can find the needles, spray bars and C clips.  You said you're stationed in Korea, so I would think all three can ship to your APO address.  Might take a little while, but you'll eventually get them.

Thanks for standing on that wall.  I sleep well knowing you're there.
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Post  Dave P. on Thu Nov 15, 2018 7:40 pm

While you're ordering parts, you might want to get some TD thrust washers if you plan on using a starter.  Saves wear and tear on the crankcase and drive plate.  

I'm guessing that the backwards thing is a result of the cold weather and the resulting need for heavy priming.  I'm no expert, but that's been my experience.  Awful cold there right now I'll bet.
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Post  Cribbs74 on Thu Nov 15, 2018 11:49 pm

So Ken already alluded to your problem, too rich and it will do that, it’s not a Cox phenomenon either. I’ve seen and done it on many front rotor engines.

My guess is the needle you chose to use is not correctly tapered. Allowing too much fuel to enter.

There are you plenty of sources for parts. Shouldn’t be hard to find or aquire. Even in Korea.

I love Korea, especially the food, I wish I had a hot Dolsot full of Bi Bim Bap and a big pile of Kimchi right about now!
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Post  Iceberg on Fri Nov 16, 2018 12:56 am

Thanks all I'm trying to get the right parts to get these motors running good soon. Will do so no question about it.

Much appreciation.

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