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Why does engaging first gear always clunk?

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by Kyba274, May 2, 2010.

  1. Ive been wondering of the reason for this for awhile.
    Every bike ive ridden, when engaging first gear there is a loud clunk noise and the bike jerks forward a little bit. Then changing from 1st to 2nd is also a little rough, but then each gear upwards is fine...
    Whats the mechanical reason for this? and is it present in all bikes?


     
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  2. think this was asked a little while ago. my guess would be because it is the biggest ratio jump in the gearbox.
     
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  4. I should learn to read,

    this is also asking about 1st to 2nd, and then up through the box while moving. Can't see the answer being all that different from them.
     
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  5. :rofl: x10000
     
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  6. 1) Most motorcycle clutches use multiple plates, which do not free completely (and separate fully from the adjacent plate) because they are contained in an oil bath (the gearbox or engine/gearbox oil).

    Consequently there will still be some spinning of the input shaft when the gear selectors select whichever gear is there.

    Even dry clutches still do not completely free when pulled in, and you might have to wait for 10 or 20 seconds for the input shaft to slow or stop, before being able to make a noise-free selection.

    You could also find, if you do that, that the gear will not actually engage because it has stopped at a point where the engagement "dog" cannot fit into its mating slot(s). That's a little bit like what happens (except in reverse) when you hold the clutch in too long while coasting to a stop, or stop in gear and are unable to select neutral.

    The "clunk" is not a sign of a problem, nor is it a problem in itself.


    The difference in gear speeds between 1st and 2nd is usually greater at the bottom end of the gearbox, hence there can be more noise because the sliding "dog" has to mesh with another "dog" spinning at a different speed..

    However, a skilled rider will compensate for this by preloading the gearchange lever slightly and experimenting until he (or she) finds the correct "speed of lever operation" to make a clean, noise-free change. It's possible.

    But once again, this is not really a problem.

    Most bikes have this issue, but most good riders learn to change to minimise it. It makes you look better...or sound better. ;-)

    The higher the gear the less difference in speed between components, so that there is less tendency to clunk. However, if you delay the change by holding in the clutch for a few seconds, you should be able to get quite a good clunk. ;-)

    Cheers

    TG
     
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  7. Well blow me down. Howdy Trev. Welcome back.
     
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  8. Ha, that's not a clunk...

    Ask any BMW rider what a real clunk is... :cheeky:
     
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  9. That's why BM riders wear ear plugs all the time
     
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  10. Motorcycle gearboxes are constant mesh, if you have gears banging into each other, best get off and start pushing!
    When the clutch is released, the entire gear train is being spun, except that no gears are engaged to a dog.
    The bang is just the wet plate clutch getting "stuck" together by surface tension created by the oil film on the plates and causing the clutch to stay engaged. Remember, engine oil is much thicker when cold, so there's plenty of surface tension to be had!
    I've owned bikes that would bang into first so bad after a few days sitting, they'd stall.
    You can pull clutch in, in neutral and rock the clutches free, or just start the bike and pump clutch lever a few times before you engage first.
    Also ensure you are getting full clutch travel.

    Regards, Andrew.
     
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  11. Oh no please not again[-o<[-o<.
     
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  12. I do this..it makes a difference..the clunk is still there, but not as loud. It's usually only the first time I engage the gears that it happens..after the bike is warm it's glassy smooth.
     
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  13. Thanks for the responses. Trevors explanation made a lot of sense, combined with a few google images of motorcycle clutch diagrams.

    Although the clunk is always there when engaging first from neutral when stopped, no matter how warm the bike is. Oh well, just another odd thing to get used to.
     
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