Zongshen RX3: How the 6-Speed Transmission Operates

[SpudRider]

This thread will describe how the 6-speed transmission of the Zongshen RX3 operates.

Power Flow

Power from the crankshaft spins the main shaft via the clutch. Six gears on the main shaft are connected to six gears on the counter shaft. Each gear combination has a different ratio, which results in a six-speed transmission.

Gear Engagement

Some gears are fixed to the shaft in a stationary position. Some gears are fixed to the shaft, but they can slide laterally. Some gears are free to spin. In the illustration below, the free gears are marked with an white 'X.' You will notice that free gears are always located opposite fixed gears, and vice versa. At the moment, the transmission is in neutral. The gears of the main shaft are numbered.



If a gear is fixed to the shaft, but can move laterally, it moves along splines. The next photograph shows the splines on the shaft (A), and the splines inside the gear (B). Lumps on the gear called dogs [C] allow the gear to lock with adjacent gears.



When a gear which is locked to the shaft slides into an adjacent gear, the dogs lock into holes on the adjacent gear. Although the adjacent gear is a free gear, when the sliding gear connects with the free gear, it locks the free gear to the shaft. This is how gears are selected from the transmission. Once locked, the formerly free gears can drive the opposite gears on the other shaft of the transmission, and power is delivered to the sprocket.



Choosing a Gear from the Transmission

When the transmission is in neutral, every fixed gear is aligned with a free gear. Since the free gears spin on the shaft, no power is delivered to the sprocket. This is the situation shown in the illustration below.



However, when you select first gear, one of the locked gears on the counter shaft slides to the right, and engages the adjacent free gear, locking it to the counter shaft. Power now flows from gear #1 on the main shaft to the opposite gear on the counter shaft, and power is delivered to the sprocket.



Examine the next five photographs. In each case one of the fixed gears slides laterally to engage one of the free gears, and locks it to the shaft. Please note, when you change gears, the previous gears must disengage before the next gear can engage. Obviously, you can't have two gears engaged at the same time.











You might ask, what makes the fixed gears shift back and forth to engage the adjacent gears? If you look inside the orange ovals in the photograph below, you can see each of the shifting gears has a grooved surface which accepts a shifting fork. Each shifting fork has a knob which engages the grooves on the shift drum. As the shift drum is rotated, it activates the shifting forks which move the fixed gears, and shift the transmission.

[SpudRider]

The following video shows how the forks shift the gears through a 6-speed transmission.

[SpudRider]

You might now ask, what makes the shift drum move when I tap the shift lever with my foot? Inside the orange oval of the photograph below, you can see how the gears, shift forks, and shift drum are installed in the crankcase.



The top of the shift drum extends into the right crankcase cover, where it is capped with the shift star. When your foot taps the shift lever, it actuates the shift pawl. The shift pawl engages, and rotates the shift star, which actuates the shift drum. The shift pawl and shift star are located inside the red oval in the photograph below.

[SpudRider]

Starting at the 8:30 mark, the following video shows how the shift pawl operates the transmission.

[SpudRider]

The following video brings all the pieces together, and briefly shows how a motorcycle transmission operates.

[SpudRider]

If you watch the three following videos, in sequence, you will see a detailed explanation of how a motorcycle transmission operates.

[SpudRider]

[SpudRider]

[SpudRider]

Here is an excellent photo of the NC250 transmission I found on Taobao. The gear dogs and gear engagement mechanisms are very evident in this photo.

[3banger]

Excellent photo description spud. I always found the sequential gearbox to be ellegent and simple. I've never quite understood why it's not standard on all manual shift engines.

Now could you do the same for the hydraulic goo black box of magic & mystery that is an automatic transmission?

[SpudRider]

Originally Posted by 3banger

Excellent photo description spud. I always found the sequential gearbox to be ellegent and simple. I've never quite understood why it's not standard on all manual shift engines...

Thank you, mate. Indeed, the design is robust and elegant.

Originally Posted by 3banger

...Now could you do the same for the hydraulic goo black box of magic & mystery that is an automatic transmission?

No, I don't even want to try.

[FastDoc]

Thank you Spud for all the hard work that you put into this picture thread. I am also grateful to the anonymous person who made that YouTube video. After 35 years plus on motorcycles, and working on them, I don't think I have had a better understanding of how a transmission works than I do now, thanks to you and are anonymous YouTube buddy.

The motorcycle transmission is a remarkably elegant, efficient, durable, complex, yet simple part of the machine that I really appreciate now that I learned more about it. It is amazing that it was never invented in the first place. I don't think that it's a whole lot less complicated than the internal combustion part of the motor, indeed it may be more complicated.

It is also easy to understand now why they make clunking sounds in between gears.

[SpudRider]

Thank you, Brother Bill. Indeed, the motorcycle transmission is amazingly rugged, yet elegant in design.

P.S. Have I told you how nice it is to have you back with us.

[Jay In Milpitas]

Very nice work, Spud.

Many folks ask why it's difficult on most motorcycles to shift to neutral while at a stop.

If you look VERY close in entry #9 you may be able to see that the engaging dogs have a slight angle in the portions that mate together.
It's most evident in the pair on the upper shaft, the 2nd & 3rd from the left. That back cut forces the dogs together while they have load applied.

When you are at a stop with the bike in gear and the clutch lever pulled in, there is still drag between the clutch plates which applies load against the dogs.

So when you are trying to find neutral at a stop, it takes more effort with the toe to move the shift drum because the dogs don't want to release. Add to that the knowledge that you only want to move the toe shift lever a tiny bit and you start to tense up. Suddenly Second, now First again,,,,, darn it!

Anyway, we've all been there, but hopefully now you understand why.
And practice catching neutral before fully stopped.

[Jay In Milpitas]

And just a bit of gear-head porn here.








I will save you the trouble counting. Fourteen speeds.