Medalion/TD

Sure you can run a Tee Dee on a wedge tank.  In fact, with the stock needle valve assembly running a pressure bladder can be kind of tricky.  The needle thread is a bit too coarse for adjustment under pressure. It works fine with a plain tank.

They look similar, but they're actually quite different. The main differences between the Medallion and Tee Dee are the crankshaft, the carb body/venturi/needle valve assembly and the cylinder.  The Medallion crank has a smaller, round port which makes it a bit more docile.  The TD crank has a rectangular port so it breaths better, but has reduced fuel draw. The web is thinner on the Medallion crankshaft and early TDs than the later model TDs as well, so the crankcases may look the same, but internally, the Medallion and earlier TDs have a slightly longer front end. They aren't interchangeable.

The carb body/venturi on the Medallion are one piece plastic with the needle valve assembly basically a tube.  The TD has a separate needle valve assembly and aluminum venturi.

The TD has a #4 cylinder, the Medallion usually has a #1 or #3 cylinder.  Cox probably made some with a #2, but I've not seen one so I don't know for sure.

The Medallion isn't as powerful as the TD, but it is generally a more user-friendly engine.

Thanks Dave!

About the post on the side of the carb body, as 1/2A Nut said, it is usually used as an anchor for a starter spring.  But according to the directions that came with the engines, it was a nipple that could be drilled out through the crankcase to use for pressurizing the fuel tank, allowing you to drill out the venturi for more power.  

They added in the instructions that the gains would be minimal.  I never tried it and don't know of anyone that has so I don't know how well it worked.  I've seen more broken off posts than drilled out crankcases so I have to think it wasn't a real game changer.

Drilling the case isn't a good idea. It can cause a lot of run issues such as the engine surging up and down in rpm's due to air leaks and the pulsing of the valve timing. The nipple was used for crank pressure, the nipple was too small and it's tapered causing the fuel line to constantly leak and fall off. The Knights Of the Round Circle had a few flyers such as Larry Renger ( Former Cox engineer ) who used it exclusively for stunt. I think it was more of a experiment than a advantage but he successfully made it work using a Foremost one way valve in the pressure line. Backplate pressure is easier to deal with and the real problem initially was the recommended hole size through the backplate and or case. You only need a pin hole for this to work effectively and the size escapes me currently which was too large. The problems faced with using case pressure is that when you turn the prop, your automatically forcing fuel up the line and into the engine, therefore a pinch off device is required to start the engine. The same type used for bladder. A bladder requires a fine threaded needle valve whereas the stock setup will work on case pressure.

I have used this on two engines in the past and the real problem is that you forget that the case is drilled. The engine will run with the hole in the side of the case but it will run poor. Until the hole is sealed, it becomes a real headache due to not being able to see it without removing the carb body. I drilled out the case and JB welded in a piece of aluminum rod to seal it.