What Medallion is this?

I’m still unclear what the ring is for. It spins in the groove but doesn’t change anything in the grove it rides in. Can someonevplease explain it in simple terms. The way it looks now if I completely remove it it will have no effect on the engines performance

I’m  still unclear what the ring is for. It spins in the groove but doesn’t change anything in the grove it rides in. Can someone please explain it in simple terms. The way it looks now if I completely remove it it will have no effect on the engines performance
Thanks

kaplangmk wrote:I’m  still unclear what the ring is for. It spins in the groove but doesn’t change anything in the grove it rides in. Can someone please explain it in simple terms. The way it looks now if I completely remove it it will have no effect on the engines performance
Thanks

The ring is a throttle. It changes rpm by blocking the exhaust. Block the exhaust, engine slows down. Open exhaust and engine speeds up.

Check out this YouTube video by our member Kim Stricker. He explains its function in the text at the beginning.. and then shows its function while the engine is running.

For these small engines, throttling or choking the exhaust gas release has the same effect as air intake carburation. However, one thing to note is that this action is not linear.

The ring's half open exhaust is not half throttle, it is more like 2/3rd to 3/4th throttle. Open about 1/3rd is roughly half throttle.

It works very effectively well for its simplicity. It is one of the most trouble free throttling systems around.

I was able to make my venerable Cox .049 R/C Bee, an exhaust throttle reed valve engine to function "linearly" with my quick blip sequential KRD throttle servo on my old Ace R/C Pulse Commander rudder only system. It had a single push button that one would tap with their finger.

For a normal R/C carburetor, it would command RPM's of High, then Medium, then Idle, then back to High. It's servo wheel went in one direction. When I used the servo with my "1965" OS Max .10R/C, it worked perfectly.

For the R/C Bee, through trigonometry, I figured out how to make the KRD throttle servo work with its exhaust throttle ring. I fenegaled it by:

1. Pushrod in servo wheel all the way forward, (0° for reference) exposed the exhaust notch in the ring against the forward edge of the cylinder's exhaust slot for idle. (It had this notch cut in the ring's exhaust window, not all rings have this.)
2. Then all the way back (180° rotation) pulled the ring back until 1/3rd of the exhaust port was exposed against the cylinder's rearward exhaust slot edge.
3. Next blip to mid servo wheel postion (90° rotation forward) held the ring in fully exposed exhaust for full throttle.
4. Back to Position #1 with a 90° rotation for again idle. Wash, rinse, repeat.  

Back to the math, I was able to figure out where to drill a new hole in the servo wheel from the center for the engine pushrod, so that the range of motion would do exactly all of the above. My scheme reversed the servo's action so now it was Idle - Middle - Full throttle back to Idle, but I still had a blast with Minnie Mambo.

Flying my one and two channel half-A and A planes in college in the late 1970's / early 1980's helped me to maintain my sanity.

Ditto flying my planes while working in aerospace, too.

I hate to be a burden here but I’m not getting any answers that help. The video also isn’t any help because it’s hard to see the throttle.
Let me try again.
The ring on my Medallion when turned does not cover any part of the exhaust port. It looks like it’s there for no reason at all. I could remove it and it will have no impact on the engines performance. Cox must have put it on the engine for some reason but why is a mystery to me.
Thanks

Found this Medallion throttle picture on EBay.
Sort of looks like mine. I’m thinking the throttle sleeve is frozen on the cylinder and isn’t turning with the ring. When I get home I’ll have to check

That ring, the thin circular bit with "ears" that have holes in, is called a "circlip" in the UK. This one is an "external" type. The holes in the eyes are for the ends, the "pegs" of a special pair of pliers, external circles pliers, that when the pliars handles are squeezed together, the pegs go further apart.

A lever type that I cannot remember the type of, a lazy fart probably

To remove the circlip, use suitable external circlip pliers to expand the spring steel circlip enough to slip off

Be warned, recessed internal combustion engine clips need carefull treatment, respect, technique and internal circlip pliers.

Break an ear off one of them and have great fun !!!!!!!!!!!!!!!!!!!!

Yes u have been warned.

Yes have a hydraulic disc brake bike ????

Problem solved!
The sleeve was frozen. Took cylinder off, removed the glow head and soaked the cylinder in some lacquer thinner. It easily then came off. Put it all back together and now it moves as it should..
Thank you all for your input
Much appreciated!

My circlip removal tool. Did use it to remove the clip

Glad you solved your problem, @kaplangmk . Now that it is freed up, hence forth it should be reasonably easy to re-orient the servo "C" clip by hand so the throttle ring can be aligned to your servo action.

You'll find that this type of throttle is very foolproof, works effectively, and is basically troublefree.

You probably already know this, also a good help is the engine manual section of this forum available for download as PDF's at the bottom of the Latest Topics list if you are using a desktop browser.