Tranny questions

[DrunkenEskimo]

All right, I've been having a problem shifting first to second, as in, second doesn't work at all, pops back to neutral when I let go of the clutch and try to hit the gas. Now I did a search on the troubleshooting forums for "Transmission" and the first three or four results were almost identical to mine.

Now, here's the question, how do motorcycle engine/tranny's work together? The two things I heard on all three of those posts was "check your shift linkage" but even more so: "bent shifter fork."

Does anyone have a good explination on how motorcycle trannies work or have a link where I could find some good info on this? LoL, wtf is a shifter fork?

[TechTMW]

First of all, different motorcycles use different gearboxes and gear actuation. What bike do you have??

On an American (Harley) or German (BMW) setup, you can simply unbolt the gearbox from the engine (Or frame) and fix it separately. Some newer bikes (BMW and others) also use a casette type transmission, which means you can take the gears out of the crankcase without having to dismantle the whole engine.

I'm going to assume you have a typical Japanese setup - The engine, Clutch and Transmission share the same crankcase oil.

When you hit the shift lever up and down, it rotates a "Shift Drum" which has notches in it. Fork-looking parts ride in the notches and slide right or left, sliding a gear along a shaft, which engages the drive gear through means of Dogs (Usually). Dogs are metal posts that stick out from the side of the gear and fit into slots machined into the gear nest to it in order to get it to turn. Either your shift linkage (The pedal) is out of adjustment - And not fully rotating the Drum, or the 1st-2nd gear Fork that rides on the drum is bent - thus causing the gear to not slide into place. There is also the possibility that the Dogs have been chipped or worn to the pont that the gear will no longer engage. Typically, a bent fork (Caused by someone who doesn't know how to shift) will cause partial engagement of the dogs on the gear - which in turn causes excess wear.

Pedal adjust ment is a simple fix - bent fork and/or worn dogs (Probably) means you have to split the cases, and replace the parts.

More info here - http://www.dansmc.com/gearbox.htm

[DrunkenEskimo]

1994 suzuki Katana, so yeah, basic Japanese setup really. Thanks a bunch for the link, now if I could just decipher it.....


Edit! I think I got it. Shifter forks move the dogs which locks the gears right?

Edit edit! So for any motorcyle with multiple gears, there are an equal ammount of shifter forks and dogs right?

Edit to the 3rd: Or is it just half as many 'cuz you can move a dog from one gear to the gear next to it?

[TechTMW]

Not quite - Dogs are actually on the gear - so if the dog is worn, you have to replace the whole gear. Number of forks usually depends on transmission setup. If I had to estimate, I'd say that three shift forks are common - because one shifter fork can slide a gear either right or left, so it really controls 2 speeds.

I know it's tough to decipher - basically it's like this - If adjusting your shifter linkage (Outside the engine) doesn't work, you're either going to have to ride without second or take the entire engine apart to fix your problem (Because I'm pretty sure a katana has a horizontally split case)

[DrunkenEskimo]

Now I'm a bit confused. This is the picture here I looked at to kinda make this assumption:

http://auto.howstuffworks.com/motorcycle1.htm

To me it looks like the gears on the "To differential" Shaft are free spining until the "Collar" (That's the dog right) that is locked onto the shaft locks into it, which then spins the shaft in a new gear right?

[TechTMW]

That's a pretty simplistic diagram. Roughly that's how it works.

What you should be concerned about is those little bumps sticking off what they call the collar - those are the DOGS. That's what catches the gear , and what may be messed up in your bike. Or, if the shifter fork is bent, the dogs never properly engage

[DrunkenEskimo]

All right! Thanks for the help, it's very much appreciated