How a Motorcyle Transmission Works

I figured that this would be good to link for people who are new to motorcycles, or who have never worked on the innards of one.



The only thing I don't understand is why there's a sprocket on the output shaft.
Makes no sense at all

 

+

It's a conspiracy from big oil to sell people chain lube.

 

Kind of amazing transmissions work and run as well as they do....given how many moving parts, etc. there are.

 

And to sell shop cloths to wipe excess dirty oil from hands, chains, etc....

 

So what is the noise on my 750 Seca when shifting? It will glide into second, but clunks into 3rd and 4th, and glides into 5th. The clunk / almost grind at times is pretty annoying and definitely gets worse when hot- is that fixable? Oil is Castrol Actevo motorcycle oil 20W-50, clutch cable is new, and adjusted to 2mm free play.

 

Clutch cable adjustment. The clunk is from the dogs not sliding into place easily because the clutch is not fully disengaged.
To confirm try shifting without the clutch. Preload the shift lever with your toe, quickly roll off the throttle, and the gearchange should happen quickly, smoothly, and without any clunk.

On most bikes of the era (including the XJ) there is a compromise that has to be made; either it clunks into first, or it clunks into all other gears instead.

 

The channels on the selector drum in the animation, that is where the bits of alternator/starter chain guide breaking up cause the gear selection problems on our XJ's eventually. Good animation to help explain that k-moe.

 

do that enough and you find out how a transmission works, first hand

 

I guess I was thinking that smooth to 2nd and 5th and clucky to 3rd and 4th might mean something is worn or damaged - it does have the original clutch. Maybe a bent or worn shifting fork?

 

I've done it a bunch. No problem at all so long as the transmission itself is in good condition. Pneumatic shifters for drag racing do essentially the same thing, but cut ignition momentarily instead of cutting fuel.
It's a good skill to have if your clutch cable breaks and you don't carry a spare, though downshifting takes a lot of practice to do well (I don't recommend it except as an emergency measure).

 

A bent shifting fork normally results in not being to engage a gear at all, or popping back out of gear. The clunk comes from the fixed gears spinning too fast for the dogs to engage their slots smoothly.