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That mysterious first gear clunk...

31K views 11 replies 10 participants last post by  mcfcinusa 
#1 ·
I have a new 2012 Bonnie Black with barely 300 miles to it, still in the break-in period.

Sometimes whenever I go into 1st from neutral, there is a very loud CLUNK sound. And then sometimes there is no sound at all, a very easy transition.

I blip when I upshift and downshift. Not really riding it very hard.

I also sometimes hear it with other motorcycles on the road. I seem to remember a similar phenomenon with my first bike, a Honda Nighthawk CB250.

Can anyone explain to me (a not-very-mechanically-inclined noob) what is happening in the bike for it to happen just sometimes?
 
#2 ·
What I have been told long ago is that when not engaged your drive is not spinning or slowing. So when you engage with a spinning gear you can get a clunk or a grinding. Preloading your shifts helps quicker shifting which will take care of the 1-2-3. Neutral to first the motor should be at idle. I normally recommend staying in gear at lights and traffic (Its a safety thing). I'm sure there is someone on here who completely disagrees with me and I'm A-OK with that.
 
#3 ·
You'll also find that as your Bonnie breaks in, the tranny gets much much smoother. The transmissions on the Bonnies are fantastic. At 25K on my Bonnie, it's like butter. My RT on the other hand is like shifting a tractor.
 
#4 ·
Hard to explain in layman's terms. It has to do with the clutch pack not fully releasing. There are lots of reasons why it may (or may not) fully release. Oil temp, previous plate separation, oil viscosity, oil additive packages components. Shift fork dog fitment in shift drum.

The easiest way to minimize it is to "pause" after you pull the clutch lever in for 1~2 seconds, THEN apply pressure to the shifter pedal. (From N to 1st.) Try it and see if it helps.
 
#5 ·
Yeah, all of the above and everything arbeach wrote is all Greek to me. I have a very basic understanding of how a motor works and how the power is transferred to the wheels. But once you get any deeper than that, I'm lost. I do appreciate the suggestion and I will indeed try it and report back.

Thanks!
 
#6 ·
While '02 Daytona 955i gearbox is as smooth as butter, my son's '06 Honda Fireblade also 'cluncks' into first gear even though is seamless between gears. I have found this to be the case with a number of other Japanese Superbikes I have ridden over the past years. Nothing too mysterious and not a big deal really...

 
#7 · (Edited)
A clunk going from neutral to first is common on most bikes as the clutch plates stick together a bit because of the oil. It's worse when the engine is cold. Put it into gear and the transmission starts to pull, then the loading hitting the clutch causes the plates to fully separate and release. The clunk is the slack in the chain and gears taking up.

Rob
 
#8 ·
A clunk going from neutral to first is common on most bikes as the clutch plates stick together a bit because of the oil. It's worse when the engine is cold. Put it into gear and the transmission starts to pull, then the loading hitting the clutch causes the plates to fully separate and release. The clunk is the slack in the chain and gears taking up.

Rob
Partially, but mostly within the clutch basket.

Let's see if we can get this by the mods~

The chain slack and gear clearances is called "driveline s natch" Most noticable in vehicles with a differential.

I'm not sure this will get through but that's what it's really called.
 
#9 ·
:Not again

Please be aware that it's not the mods; it's an auto-censor with a dictionary that we don't currently have control over.

Cheers,
-Kit
 
#11 · (Edited)
It's quite normal. My Thruxton does it, and they have the same gearbox as the Bonny. Its because the gearbox internals are spinning when you first pop it into gear. Try waiting a little longer after pulling the clutch lever in before depressing the pedal.

The oil in the gearbox causes the clutch plates to drag a little when the oil is cold and thick. It is more noticeable when you first put it into gear.

I think (and I am a gearbox noob too) that there are some hefty components engaging when you go from neutral or second to first, called 'Dogs'.....like quadrant type things on the side of the gears.

It will do it if you go into first from second, when rolling up to a junction and the wheelspeed is too great. I try to avoid doing that, as it makes it clunk louder. I was always told that can stress the gearbox.

From what I have read on here, the gearbox is over engineered anyway.

Yamaha R1's do it, my mates makes a good old 'Bang' when you pop it into first.

Don't panic, Captain Mainwaring, don't panic!!!

:)

Attached is an exploded view of the gearbox components. The dogs are the segments sticking out of the side of some of the components, that locate with other components, depending on which ratio is required. (Look at components 4, 12 and 13).
 

Attachments

#12 ·
The gears are always in mesh. They only rotate. The sliding dog is what transfers the power from one gear to the shaft. The shift forks move the sliding dog from one gear to the next, each sliding dog can only serve two gears one to the left and one to the right. The dogs and gears are very hard and tough. the dogs normally have a slight angle so that they can "pull/latch" into the mating gears.
 
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