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Whirring Noise

Discussion in 'Bling and Appearance' started by RobE, Jan 4, 2008.

  1. I always feel a dill trying to explain a mechanical noise, but here I go again.

    1995 CB 250, done 75,000. Seems to run fine and nearly always does what she is told.

    We have not travelled all that far together so I am still learning her little ways.

    Just running normally on the road I become conscious of an engine rev related whirring noise. Sort of like that sound you associate with a shaft drive.

    The chain seems properly adjusted.

    I like to know what my machines are trying to telling me. Any suggestions?
  2. Are you sure its an engine rev related whirring or could it be speed related?
  3. Could be speed related. I am only conscious of it when we are moving.

    Maybe on a downhill I should try putting the clutch in or even finding neutral when I get a big piece of open road to myself?

    (If I do shift to neutral I better remember to go back to the top of the gears after. I already had a tiny thrill from shifting down too hard too fast and feeling the back wheel step out while the bike yelled at me not to do it again.)
  4. A tight chain will create a loud whirring noise, which increases in intensity and frequency (pitch) according to road speed, rather than engine revs.

    Check the chain slack at the tightest point on the chain. Anything else and you will end up with a tight chain, which actually gets tighter as it gets hotter...


    Trevor G

    PS Chain slack should probably be between 30 and 40 mm. Slack, versus play. If not sure of the difference, ask. :)
  5. wats the diff trev? :grin:

    and dont go telling what a differential is :p
  6. ooooh!
    explain that one :grin:
    all my knowledge of materials science says it cant, tell me, tell me!

  7. Slack is just that - you lift the chain up without any pressure applied, until it stops moving.

    Play is when you press down and up and exert a small amount of force just to make sure the chain won't go any further.

    The chain is supposed to have x" amount of slack. If you adjust it for that same amount of play the chain will be too tight.

    I cringe whenever people talk of adjusting chain tension - they might mean slack, but tension is an entirely different thing. Believe me, I hear enough bikes with L and P plates (and sometimes without) whizzing by, litterally, because someone got it wrong.


    Trevor G

  8. ah, so you're the technical moderator now!!?? j/k

    You made me think why it happens, and I think this is the correct answer.

    Before I get into it, though, are you genuine in suggesting that you have never adjusted a chain too tight and ridden it, and found out? Is all your experience on belt-drive harleys??

    The main bearing and wear area in a chain is the inside pin. This oscillates inside the bush. When a chain wears it is not the side plates which stretch as much as it is wear between the pin and the bush which occurs.

    The proof of this is what happens when you turn a chain on its side - a new chain will stay reasonably straight, an old chain will "bend" down in a major curve, depending on how worn it is.

    When the chain is too tight the friction in the pin/bush area is increased, and the temperature of the pin rises. This results in expansion of the pin, which then reduces the amount of play in the bush. This is the same as having a slightly less-worn chain for the same adjustment.

    The further you go, the hotter it gets and the tighter it gets.

    I know this tightening effect occurs because I have been foolish enough to over-adjust a motorcycle drive chain on several occasions. On the most recent occasion I picked up the VTR250 from a friend's son. He was a motorcycle mechanic; while he mainly worked on shaft-drive Moto Guzzis at the time, he should have known better. He had owned chain drive off-road bikes, and had been to TAFE, altho his training as a mechanic was for cars.

    I had asked him to service the bike, since he had been using it without my approval. When I picked it up, just before closing, I checked the chain and reckoned that he had taken it up a wee bit too much, but because of the time, I said nothing and went on my way.

    Within 30 km the chain was whirring and was noticeably tighter. By the time I was 2/3 of the way home (another 50km or so) it was noticeably whizzing. At both points I stopped and checked: the chain had tightened up even more the further I went. For various reasons I did not bother to adjust it on the ride.

    All the best

    Trevor G

    PS When cool, the next day, the chain was just as loose as when I picked it up. Or is that just as tight??