Chainring issues?

zanes
zanes Posts: 563
edited December 2010 in Workshop
All,

Am in need of some forum knowledge on this one ;)

Recently (last week) I've had intermittent "skipping" (drive disengaging violently and re-engaging) whilst pedalling (usually just after pulling away). Twice (including once tonight) it's been about half a revolution of the crankset.

Now, for a while I've had a bit of a "crink" noise whilst pulling away or engaging drive after freewheeling (pretty routine). It's almost a sound as if the missing link is coming partially undone, and then snapping back in. That's not accompanied by detectable pedal slip. I'd just accepted it as a quirk and didn't think much of it, until this jumping started to happen.

All cassette ratios engage well and smoothly and no jumping about between ratios is detectable (running quite nicely atm-occasional trouble on granny ring when lugging up hill but a quick adjuster twist fixes it- just a bit of cable strech and not like the current problem). New cassette and chain c.200 miles ago.

My suspects are freehub or chainring wear. The chainrings are original to the bike (4+ years old and god knows how many 1000 miles!).

Do you think the chainrings are possible suspects? I'm leaning towards them due to the "half revolution" nature of the slippage.

I have no idea of typical lifetime (a brief check on CRC makes me suspect not indefinite as I suspected due to the range they stock) of the rings. Living and commuting in Bath combined with a 23-13 cassette means most of the time the bike runs on the middle ring (it's a triple).

Annoyingly it's hard to do a visual location as it's intermittent and both times it's really happened I've been busy (pulling onto roundabout and hill climbing).

Any other ideas?

Comments

  • Monty Dog
    Monty Dog Posts: 20,614
    Chainrings have to be extremely worn to have any influence on shifting. It could be a stiff link in the chain, particularly as it passes through the jockey wheels. Also check the chain carefully for splayed links, cracked sideplates etc.
    Make mine an Italian, with Campagnolo on the side..
  • zanes
    zanes Posts: 563
    Thanks Monty, I'll have a good nosy at the chain this weekend.

    I should point out front shifting is fine, and this problem occurs when giving it some in-gear wellie.
  • Pokerface
    Pokerface Posts: 7,960
    I would never disagree with Monty as he knows his stuff - but I had what seems like a similar problem a few years ago. Same violent slipping of the chain, etc.

    In my case - it WAS worn chainrings. And they were only a year old (although with lots of miles).

    So - don;t rule it out, especially if the ones you have now are 4 years old. A visual inspection should show the teeth to be quite rounded instead of sharp. And it doesn't even have to be all of them!
  • keef66
    keef66 Posts: 13,123
    Skippy type stuff is usually caused by:

    New chain on a worn cassette; cassette wear isn't neccessarily visible to the naked eye.

    Frozen or worn our freehub internals

    Badly worn chainring; wear is obvious on visual inspection.


    My money's on the freehub. Whip it off, flush it out with degreaser, generously fill with oil, and see if normal service is resumed. If not, replace the thing.
  • zanes
    zanes Posts: 563
    keef66 wrote:
    Skippy type stuff is usually caused by:

    New chain on a worn cassette; cassette wear isn't neccessarily visible to the naked eye.

    Not that, had it briefly earlier in the year when I swapped a new chain onto the old casette- cured that and it doesn't feel or sound like that this time round.
    Badly worn chainring; wear is obvious on visual inspection.

    I had a quick check this morning and I couldn't see much out of order- but I'm not overly sure what I'm looking for, I'll probably post a picture of the ring teeth tonight for some expert forum advice.
    Frozen or worn our freehub internals

    My money's on the freehub. Whip it off, flush it out with degreaser, generously fill with oil, and see if normal service is resumed. If not, replace the thing.

    I'm possibly leaning this way, it seemed better on the way in with the warmer weather today. I've got a quote request out with Extra UK for the easton bearing drift kit atm.
  • sheffsimon
    sheffsimon Posts: 1,282
    Does it happen on both chainrings?

    Had it myself with a worn chainring, spent ages fannying around with chain, derailleurs etc, then swapped the chainring and it was sorted.
  • Pokerface
    Pokerface Posts: 7,960
    Worn chainring teeth often have a 'shark fin' appearance - worn more on one side than the other and it can happen on inner and outer rings - just depends how much you ride in each ring.

    Example:
    chainring_lo.jpg
  • Gary D
    Gary D Posts: 431
    My money would be on the freehub.
    With this extremely cold weather, the grease or oil inside will become very viscous. This may prevent the pawls engaging properly and will cause the slipping you describe.
    First of all, take off the freehub and clean and degrease it and then use some light grease and re-assemble.

    Hope this helps.
    Gary.
    Fungus The Muffin MAn wrote:
    Oh and I feel like I've been raped by an Orangutan :shock: And I've got legs like Girders :lol:
  • Pokerface
    Pokerface Posts: 7,960
    SHould be easy to tell if it's the freehub or chainring. If the chain stays tight to the chainring while the slipping occurs - it;s coming from the back (freehub/cassette). But if you can see the chain slipping across the teeth, well then....
  • zanes
    zanes Posts: 563
    Here's some pictures of the "suspect" ring- apologies about the state but a week of commuting takes it's toll on cleanliness. Looks OKish to me, what do you say?

    snb22283.jpg
    snb22284.jpg
    snb22285.jpg
  • Monty Dog
    Monty Dog Posts: 20,614
    Chainring doesn't look too worn to me - it takes a distinct assymetric profile - see previous pic - where there is no rounded trough to engage the roller, just a flat ramp. Further to previous posts, on reflection agree that sticky freehub is likely problem. Run some oil in to free-up the pawls
    Make mine an Italian, with Campagnolo on the side..
  • badhorsy
    badhorsy Posts: 107
    Hey,

    I actually just had a problem with this until recently. I was getting intermittent drive train engaging/disengaging similar to what you described, but mine was also accompanied by a grinding noise whilst pedalling, which would only kick in after about 20 mins in the saddle.

    Turned out to be the freehub. I've got a Specialized Secteur, and the freehub is some arbitrary stock part, which isn't easily serviceable. That said, my LBS were able to take it apart, realized the problem was coming from a dodgy seal which had let in water and caused the pawls to completely rust. They oiled everything up good in an attempt to get through the winter - I'm now saving for a nice new set of wheels and hubs though!
  • zanes
    zanes Posts: 563
    Cheers guys- guess the freehub is the first port of call for this now :)

    Badhorsy- happily these are upgraded wheels- Vista SL's from Easton, so the freehub is available as a separate spares item. Annoyingly the main bearings have to come out before the freehub can be removed, currently waiting on Extra UK (Easton's UK distributor) to get back to me with a price on the bearing drift kit. Got in touch with Easton first, they're very helpful over in the US but advised it'd probably be far cheaper/quicker to go through Extra over here.

    Will also be querying warranty length- two year old hoops that have actually been in use (not particularly hard use at that, <2.5k miles I suspect) for about half of that. Very much suspect I'm on a hiding to nothing but it won't hurt to ask, especially if I get inside and it's in very poor condition. Having never stripped one off before, not sure what to expect.

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