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Gearbox output bearing(s) noise?

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by DragonCypher, May 14, 2010.

  1. Bike: 1984 Honda Integra / VT250 F-II D
    MC08 Engine, 6 speed gearbox


    On cold mornings, where its been around 0C overnight, and still below 5C when I set off.. I can hear a rather loud grinding noise consistent with wheel speed.
    The noise is very similar to that of a car accelerating in reverse gear, getting louder as I increase speed. It stops when I drop below about 5km/h and usually stays quiet for a few minutes if I don't go over about 40km/h, else it starts up again.

    I'm pretty sure its not the rear wheel bearing as I've tried using the rear brake excessively to heat it up and the noise still came back.

    The other possibility I can think of is gearbox output shaft bearing, since its independant from engine speed.

    I don't have the tools or confidence to take out my engine and seperate the crankcase considering its my only vehicle.. But would there be a way to stop it from spinning the bearing and getting worse? assuming thats what the problem is.
    I also don't want to spend a whole weekend changing bearings in the gearbox if thats not the problem.

    And to top it off, I can't replicate the problem when off the bike to listen for where the noise is coming from.

    -
    Chris



    [edit]:
    After conferring with dad for a while about it, he's confident it would be wheel rather than gearbox. Since the gearbox is constantly floating in oil the bearing wouldnt have dried out, and any noise of it spinning on itself should be muffled by the oil.


     
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  2. How much slack do you have in the chain?
    I wouldn't cost anything to get a professional opinion from your local bike shop and go from there...
     
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  3. currently the chain has about 40-50mm slack

    Been meaning to tighten it up a touch
     
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  4. Well, my guess is it has nothing to do with gearbox or output shafts...
    Firstly, is the tyre the right size for the rim?
    2, is the wheel adjusted evenly, have a look at the notches on the swinging arm?
    3, check the the tyre is not rubbing on the plastic chain guard. The distance or gap will change with your weight on the bike, so get a mate to sit on the bike off the stand and see that the tyre isn't touching the chain guard at any point in the wheel rotation... tyres are never perfectly round either....
    4, check that tyre pressure is consistant with manual, probably 36psi.....

    In many years of motorcycling and mechanicing, I can't ever remember replacing sprocket shaft bearings...
     
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  5. 1. Tyre is a 120/80/18, factory is 110.. but it does the same job, only curves up a little higher at the sides so that the entire side of the bike would be sliding down the road before the edge of the tyre is used.

    2. Swingarm is bent from a previous owner, so the notches don't line up.. However the wheel is definitely straight, inline with the front.

    3. Plenty of gap from the tyre rubbing on anything, and when the issue only arises in very cold weather I can rule out this as being the issue.

    4. Factory manual says 32psi front, 30/34psi rear without/with passenger. I run 32/32 as I never take passengers but often take luggage.



    Thanks for the suggestions so far
    Is there a way I can prove whether or not its the wheel bearing without taking the wheel off and seperating it?
    Since every time I stop the problem goes away, so I can't sit it up on the centre stand spinning the wheel to find out...
     
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