How Does A Motorcycle Gearbox Work?

In this video, Kevin Cameron looks at something normally buried inside the engine of your motorcycle: the gearbox.
In very olden times, before the 1930s, there were sliding-gear transmissions, where gear teeth actually were “crashed” in and out of engagement. But gear teeth have to be quite precisely shaped to endure transmitting very large forces of contact from one shaft to another. So the idea of sliding gears into and out of engagement was given up a long time ago.
That leaves us with constant-mesh transmissions. In order to change from neutral to another speed, there is a part called the shift drum. By rotating it, the positions of the shift forks, which move the gears, are changed. The gears have to be completely under control at all times because the last thing in the world you want from your gearbox is double engagement.
Every other gear is locked to a shaft. The gears between them are free to spin. The dogs, which are engaged and disengaged by the shift forks on the shift drum, lock the desired pair of gears to their respective shafts-clutch and output-so the drive passes through that pair and the others are freewheeled.
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[@MrLuigiFercotti]

Kevin was technical editor at Cycle many years ago, before merged with CW. They kept Kevin. As an engineering student I wrote Cycle a letter about the relative outputs of various bikes (Cycle was the only one that did dyno runs back then). Kevin wrote me a personal letter in response, giving an explanation and encouraging me to follow my interests. A great guy who has forgot more than most will ever know about engineering.

[@Winterstick549]

I've also learned a great deal about aircraft engines from his articles in CW. The man needs his own KZbin channel.

[@Ernesto_Jr.]

Knowing what's going on inside the engine makes for a totally different experience while we're riding... Thanks for sharing your knowledge.

[@robertrishel3685]

Just let the man explain everything, let him start at the beginning and explain it ALL! And how about giving him a full hour per episode so he can get somewhere. The man is a genius in terms of knowledge about motorcycling AND in the ability to correctly and clearly EXPRESS that knowledge. We need this on video record.

[@blipco5]

Yes, he is pretty much the "last word" on anything.

[@tina11ys]

Good explanation of a great explanation

[@robbie2awesome]

A fine Scottish name is Kevin Cameron. The education was also really great, thanks so much. :)

[@animesh4guhaa]

Thanks 👍 u look exactly like My grandpa, he taught me a lot, now learning from you.❤️

[@cryalowicki]

Keep this series going!

[@MrStarmissed]

Totally love it. Several Eureka moments there. Thank you so much for your work on this Kevin.

[@robertrishel3685]

More!!!! More of Mr. Cameron PLEASE,

[@gaudgaud]

Great video Kevin, you have a talent when it comes to explaining complicated concepts very clearly in just a few minutes, using exactly the right number of words!

[@GeorgesPizzaboy]

I really liked the explanation from the dogs and the different gears. I liked it especially because he was speaking very slowly but clearly and with good structure. The drum and the ratchet were a little less clearly explained imo. But I already have an understanding of how that works so it doesnt really matter.

[@remotegod255]

I don't know if it was the Harry Potter-esque background music, the high definition video, or the *excellent* explanations, but I was spellbound!!! Watched about 12 videos on motorcycle transmissions and clutches today, but I think this is my overall favorite. Thank you for making it, helps this novice mechanic a lot, as I prepare for some medium-difficulty projects on my 1981 Honda CM400C

[@blipco5]

I fear the gearbox and mine is perfect. Sometimes I lose sleep at night thinking about it. This excellent video is as close to one as I ever want to get.

[@wesleymarkmusic403]

Good explanation. I'm trying to get my head around how motorcycle transmissions work.

[@bryankirk3567]

PLEASE keep going. All of my apprentices have done way better than I have, purely because I explained what was happening in a drive-train system, from atmospheric conditions to tyre tread/surface conditions. Jet engine fuel control technology also aided their understanding of difficult concepts.

[@tristanmargot3896]

Great video explanation. Thank you!

[@SpeedRunGamingPH]

YESSS FINALLY .. kinda do understand now the how the shift drum ,stopper plate, stopper arm, shift drum pins, shifter spindle work

[@ItsAlwaysTech]

Really needed these videos!!

[@DanaPellerin]

Love this guy. Great videos!

[@ianbouchardmusic7203]

Best explanation ever. Thank you!

[@duanelr]

More Kevin Cameron, please.

[@ifixsprinters]

Great job, thanks you.

[@chrism8600]

great video, thanks!

[@sunnypaul299]

Great work

[@upsidedowndog1256]

Whoever at Cycle World decided to put KC on video was a genius. Him and Egan are the only reasons I ever read the rag.

[@the2120company]

well explained ! thank you . clear

[@pankajjaswalpk1971]

Deserves way more views and likes

[@gillesd.2277]

Great video, Tx

[@erikarneberg11]

Great to be able to put a face and a voice with what had previously only been words on a page from Mr. Cameron- I’ve been reading his pieces since he was at Cycle magazine back in the 80s. Just out of curiosity, does anyone recognize this engine? A fairly modern triple with a five speed, but it’s not a current Yamaha or Triumph, I don’t think it’s a 1990s-2000s Triumph triple, and definitely not a 1970s Laverda… I’m thinking it might be an early 80s Yamaha 750/850? Great video, I only wish it was longer, and perhaps incorporated some animation to help visualize some aspects more clearly, like the rotation of the shift drum… I could watch this all day- thank you!

[@adjbob56]

Yeah that is what I thought "an early 80s Yamaha 750/850" and they had issues with 2nd gear, which is likely why it is disassembled and not on the road. I had a 1980 Yamaha 850 triple.

[@johnsilva6392]

Thanks

[@gtmoyo5667]

🧐 good vid sir

[@paulocarreiro5855]

Alright then, we'll wait for the next installment!

[@davidmiatke6758]

Still think its magic

[@SunnyFly100]

Cool!

[@olis790]

So on my motorcycle I have roughness in second gear. What does this mean, does the whole gearbox need to be changed or just a gear?

[@dabbgk]

I got an engine that will keep shifting all the way through (5th back to neutral then all the way through to 5th again) without stopping. What in there stops the shift drum from rotating after reaching lowest or highest gear and what could cause the shift drum from being able to rotate indefinitely?

[@matthewkirsch327]

Thank you. I enjoyed this video. In my opinion, the music is distracting.

[@stmurphy4356]

Hello, the video is great and instructive, I would ask you if you can give advice, I have a yamaha fz600s2 2009 that crashes a lot when I put in first gear and from first to second, it is also very audible from third to second, why is this happening people tell me that it is normal for that model, when the oil is cold then it is great otherwise I use FUCHS SILCOLENE COMP 4 10W-40. Hello from Croatia.

[@rajkirannatarajan9276]

good bg music

[@dragpipegardenaevolutionn1994]

Top !!!!

[@WICKEDGIXXERL]

Great video everytime I shift my motorcycle into gear I cringe I hate the sound of the dogs engaging. I had a Harley Sportster 1972 the clutch was heated up and dragging I put it in first gear and the dog broke off unfortunately I was 3 hours away from home and drove it crunching all the way had to replace all the gears I was surprised it didn't blow out the side of the case those bikes are known for it

[@dsbright2167]

That's me alright. I might offer that a lot of introverts also like cats. Good to watch, thanks.

[@drewtaylor6997]

Can please explain in detail why sometimes there is a loader engagement of gears and also if it causes extra ware?

[@adjbob56]

Question doesn't make sense. "loader engagement of gears"?

[@dmcbuilds1891]

Anyone know what kind of engine that is??

[@ravonstraker5991]

I’m really confused. I’ve been thinking the output shaft is the counter shaft. Based on research and what mechanics said. So are they wrong ?

[@alexv.100]

I think he said it backwards in the beginning, which shaft is for clutch and which for front sprocket

[@spoonman73]

Can you explain why it makes such a loud clunk when I put it in first gear from neutral and has been that way with bikes as far back as I can remember? Also, why does it not do it if I shift down into first when rolling to a stop. Thank you.

[@goldentrucker7921]

spoonman73 that happens on all sport bikes. My 2009 zx10r , my friends 06 gsxr 600. Every sport bike I've ever driven. Brand new, or high mileage.

[@spoonman73]

Yeah man, happened on my '91 FZR600 back in the day and happens on my brand new bike too. Just thought they might have improved that by now lol and what the technical reason is.

[@STho205]

It is the first locking dog. Look at the clutch gears when he has them in his hands. The others lock to that one and muffle the clunk. The one down neutral and four up was designed to soften that hard clash. Originally 1st gear wasn't synchronized to the others and the movement of the shaft, so you could not shift to first until a dead stop (like reverse is now). Double clutching was also common to go from 1st to 2nd. Attempts to shift into low while moving damaged the old fashion gearbox (same in a 60s MG). Bike boxes today are not as fully synchronized as cars, therefore it is still best to be stopped or very slow when shoving it down into 1st.

[@akupehsluarketatAR]

u get a clunk on the 1st because the gears on the clutch shaft are spinning(even when u pull in the clutch) and the gears on the other shaft are not. When u kick into 1st you're forcing the clutch shaft to stop on a dime as the dog set engaged. That causes the loud clunk. You wont get this when your bike is moving as both shafts will be spinning. It is also not recommended for you to hold onto the clutch whilst in 1st waiting at the red light for too long as the clutch be slightly rubbing on the friction plate causing unnecessary wear.

[@STho205]

akupehsluarketatAR. Yep. Thus cycle gearboxes do not have a truly synchro low (close but not quite). This was common in cars in the 60s as manufacturers were moving to true synchros in 1st gear from non synchro lows.

[@carmelpule8493]

It would have been better to show a shifting drum where the peripheral skewed slots could be seen.

[@SunilSundar]

When you're at rest and going from neutral to first, and both shafts are stationary, if the dogs are not aligned with the slots, how do you shift?

[@davebob5888]

At rest....both shafts are stationary.......sometimes you can't shift. You either have to rock the bike back/forward a bit to get the rear tire to rotate the output shaft, or let the clutch out and pull it back in to get the input shaft rotating. In most N to 1st shifts from rest....the input shaft is still rotating a bit from "clutch drag" as you click the transmission lever into first (especially if the oil is cold and thick).......that is why you will feel a bit of a lurch or jerk or hear a clunk as the bike drops into 1st.

[@SunilSundar]

@@davebob5888 thank you

[@drewtaylor6997]

Can you explain why sometimes a shift into 3rd sometimes is loader engagement than other times? And also if this couses ware

[@gksalf10]

Mr.cameraman, it’s better to close up for Kevin’s finger on the gearbox!

[@Jodyrides]

I want smart, a Kawasaki factory Road racer H one or crankshaft from this guy

[@galkofer]

Is it true that motorcycle gearboxes are designed for clutchless upshifts? As in all you need to do is drop the RPM as you shift up?

[@Ngontih]

Not necessarily designed for it, but yes you can just put a slight amount of pressure on your shifter thingy and throttle back a bit.

[@upsidedowndog1256]

Punch Yes they are. At the dragstrip I only use the clutch to launch. After that I just back off throttle to shift. Its worth several tenths in the ETs to do it that way.

[@petar-boshnakov]

one somehow knows this questions will be asked :D

[@alderinerush]

Everyone needs to learn clutchless shifting. It changes the whole experience. Why it's possible is because when you momentarily shut throttle the dogs on the gears disengage and they you can shift to next gear. Greater the distance between dogs, easier it gets.

[@privateer0561]

While Cameron clearly understands transmissions, his explanation is quite fragmented and less than clear. Constant mesh transmissions are not terribly intuitive; as such, an animation is a far better method of visualizing how they function. This animation is outstanding. kzbin.info/www/bejne/nWnbn3x8m5mcmpY

[@Earthneedsado-over177]

Nice Hands-On explanation. But straighten the watch on your wrist! It's bugging me.

[@braapbrar4745]

I thought this guy was mr lahey when I seen the thumbnail 🤔

[@mattymccolgan9453]

Good tutorial but I'm still confused lol

[@wazzer5293]

Grandpa.. appreaciated the teaching effort. You could even teach me.. newbies more better by using the foot bracket/arm as changing gears rather than saying this video as general idea only.. me unable to swallow ur general idea yet..so sorry.. - newbies

[@laddaevolta]

I've watched better explanations

[@tomquinn607]

Just want to hear Kevin. Please lose the weird music.