Help.... Before I hurt myself ideally.....

Pouts
Pouts Posts: 34
edited July 2013 in Road beginners
Good Morning all....

Little advice required please.
On a short ride this weekend at the bottom of a steep descent my chain inexplicably jumped off the smallest rear cog. Stopped safely and put back on.

A little further into the ride I went to put the power down, again in the smallest rear cog and it sort of jammed for a split second before engaging and I carried on not really thinking anything of it.

On inspection when I returned home I was rotating the crank by hand and the chain appears to be jumping in the air each time it rotates a specific point on the smallest sprocket.

There is nothing visible by eye causing this but am thinking it may be slightly bent causing the jump?

For reference it is a tiagra 12-30t cassette and is approx 500 miles old and well lubed.

The question is do I need to replace this cassette before something bad happens??

Many thanks.

Comments

  • Pumpkin Positive
    Pumpkin Positive Posts: 392
    Watch trhe chain as it runs through the jockey wheels and cassette, this should give some idea if you have a stiff link or some other chain defect. Alternatively take the chain off and check it for stiff links check your chain for stiff links. One of these makes life much easier http://compare.ebay.co.uk/like/17107363 ... =66&ff19=0

    Your cassette should be OK with only 500 miles on it.
  • gozzy
    gozzy Posts: 640
    What P.P said, also, I'd be inclined to check the derailleur high limit stop if I were you just to be sure it's set right before it does go off the end.
  • t4tomo
    t4tomo Posts: 2,643
    If its jumping once every rotation of the wheel then its a sprocket issue, if its every now and again (a chain revolution) then it could be a stiff link issue. have a good check for damage on which ever it is.

    Have a look from behind the bike at the position of the derailleur in relation to the sprocket when you are on that smallest cog. if its at all right of centre then adjust the limit screw to bring it back in line. You want it so rthe chain will drop onto the smallest cog unhindered, but not drop below that.
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  • RidingSeed
    RidingSeed Posts: 33
    You should start by taking off your chain and check it really well for unusual things on it. Have you suffered any crash lately? Maybe something in there cracked and you cannot see it. Get it to an expert if you can't figure it out yourself.
  • plowmar
    plowmar Posts: 1,032
    Thanks 'Ridingseed', your answer may explain my 'jumps' on 2nd and 3rd largest sprockets when on gradients - not otherwise.

    Had a slidey off just after bike was serviced in March. Off for 8/10 weeks - cracked hip- and only noticed jump after this. Back to LBS this week then.
  • keef66
    keef66 Posts: 13,123
    If you fell off drive-side down you may well have bent your rear mech hanger. (they are supposed to do that in order to protect your frame) Needs to be checked out.
  • Pouts
    Pouts Posts: 34
    Ok so just got home from work amd checked the chain.... links all moving freely. had a close look at the sprocket....

    One of the teeth appeared to be flared outwards so I think I committed a cardinal sin....

    I tw@£&ed it with a hammer and it is now back in line with the others and the chain is now moving smoothly...

    Thanks for all the advice, about to head out on a test run so will report back later!
  • foxydan
    foxydan Posts: 83
    I would replace the chain. This happened to me and decided to do what you did. I nearly paid the price on the London to Brighton as it started to pop out again. Luckily managed to get a mechanic to push it in until the finish.

    Replace it....otherwise you might find yourself stuck somewhere. Oh and make sure you carry a chain break on your multitool and some chain links if it does happen you'll be able to repair it to get home.
  • keef66
    keef66 Posts: 13,123
    foxydan wrote:
    I would replace the chain. This happened to me and decided to do what you did. I nearly paid the price on the London to Brighton as it started to pop out again. Luckily managed to get a mechanic to push it in until the finish.

    Replace it....otherwise you might find yourself stuck somewhere. Oh and make sure you carry a chain break on your multitool and some chain links if it does happen you'll be able to repair it to get home.

    He said the chain's OK, it's the sprocket that was bent...

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