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  1. #1
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    trek 920 chainring removal

    Hi All,

    I just got myself an old (but don't know how old) Trek 920. It just seems like a sturdy little bike that I want to use for around town biking. It looks like it hasn't been maintained at all, so it requires a firm cleaning, and perhaps some new parts here and there. I'm not very familiar with mountain bikes (I road bike mostly) and kind of got stuck on the chainring removal.

    It seems like the chainrings are stamped together, and there aren't just a couple of bolts I can remove to take them off (like on my road bike). Seems like I first need to remove the cranks to get to the chainrings? True? Does anybody know what type of crankset is fitted on the trek 920? What type of crankpuller do I need (if I need one)? In other words, how do I remove these chainrings???

    I don't know what year the bike is, I estimate about 10 years old or so, and it's got the stx front and rear derailleur.

    Not sure if I can post pics, but if yes, I'll try to make one, so that you can perhaps see what I mean.

    Thanks for any input, appreciate it!

    Tim

  2. #2
    WNG
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    If it's a stamped crank, you can't disassemble the chainrings.
    Low-cost cranks are stamped units usually. Once the teeth wear out, you toss it.

  3. #3
    cab horn
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    Quote Originally Posted by WNG View Post
    If it's a stamped crank, you can't disassemble the chainrings.
    Low-cost cranks are stamped units usually. Once the teeth wear out, you toss it.
    Yeah spot on. Post some pics to confirm anyways.
    Mes compaingnons cui j'amoie et cui j'aim,... Me di, chanson.

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    Ok, thanks a lot guys! That explains it! I'll toss it then.

    So do you perhaps know what types of crankset I can get for this type of bike? In other words how do I measure if it's gonna be compatible with the bottom bracket. Preferably inexpensive, but I do want removable chainrings this time.

    Also, what type of crankpuller do I need to remove this crank?

    I will post a picture later today.

  5. #5
    WNG
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    Chances are you have either a Shimano Alivio, or Suntour XC-E stamped crank utilizing a square taper bottom bracket.
    Check Sheldon Brown's/Harris Cyclery site for bottom bracket spindle length info once you've verified the model. Then you can check if a new crank will work with the old BB.
    Personally, I'd buy a new matching BB for the new crank.

    Check out Nashbar.com for some deals.
    I picked up a Shimano FC-M340 triple crankset for $10 new. It is steel rings, but are bolted to an alumimum spider.

    You need a thread-on crankarm puller.
    Go to Park Tool site for pics and how-to info.

  6. #6
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    Quote Originally Posted by WNG View Post
    Chances are you have either a Shimano Alivio, or Suntour XC-E stamped crank utilizing a square taper bottom bracket.
    Check Sheldon Brown's/Harris Cyclery site for bottom bracket spindle length info once you've verified the model. Then you can check if a new crank will work with the old BB.
    Personally, I'd buy a new matching BB for the new crank.

    Check out Nashbar.com for some deals.
    I picked up a Shimano FC-M340 triple crankset for $10 new. It is steel rings, but are bolted to an alumimum spider.

    You need a thread-on crankarm puller.
    Go to Park Tool site for pics and how-to info.
    Thanks for the info! Got the crankpuller at a local store and got the cranks off. I agree, I think I should just get a new BB and crankset while I'm at it. Will check out that website you gave me. Any tips on good value BB and crankset combinations?

    I added a picture of the bottom bracket and the cranks/chainrings as promised.

    Now what do I measure on the bottom bracket to make sure I get the right one? The tapered squares are about 1.3 cm wide halfway, the frame width over the bb is 7.35 (with outer diameter of the cylinder holding the BB roughly 4.09 cm). Measured across the end of the square tapered pins I have 11.38cm. Apart from the measurement of the ends of the square pins, I doubt whether these measures have any universal meaning.

    Anyway, maybe the picture will help here. If I measures irrelevant measures (which is more than likely), please let me know what to be measuring before I order new parts.

    Thanks again guys!

    Tim


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    Ok, did a little quick reading on the matter (sorry, should have done that before).

    I realize now that the distance across the square tapered pins that I measured is the spindle length, right? Can anybody tell from the picture in the previous post whether this is a shimano cardridge-style bb? I've been looking at some pictures and drawings and that's what it looks like the most. But there seem to be so many different kinds that I am not positive.

    So what tools do I need to succesfully remove this BB and install a new one? Any suggestions on what I should get (inexpensive) is great!

    Thanks again!

  8. #8
    Senior Member Bill Kapaun's Avatar
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    Is there actually anything wrong with the current BB / chain rings.

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    Quote Originally Posted by WNG View Post
    If it's a stamped crank, you can't disassemble the chainrings.
    Low-cost cranks are stamped units usually. Once the teeth wear out, you toss it.
    Right, they are a "use it up and discard" component. A conventional crank puller works to remove the entire crank from the bb spindle but after than there is no service other than cleaning.

  10. #10
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    Quote Originally Posted by Bill Kapaun View Post
    Is there actually anything wrong with the current BB / chain rings.
    The bb has a little bit of lateral play, noticable but nothing too terrible. The teeth on the chainrings are fairly worn. The chain was so dirty and rusty I got rid of it and bought a new one. Since the chainrings and cogs are fairly worn I figured I replace those also (before I put the new chain on). Now that it turns out I have to replace the crankset I guess taken out the bb while I'm at it might be a good idea (because of the play).

    Open to suggestions though!

    Anybody identified the type of BB in the picture?

    Tim

  11. #11
    Senior Member Bill Kapaun's Avatar
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    It appears to be a standard cartridge type-
    http://sheldonbrown.com/harris/botto...s.html#shimano

  12. #12
    WNG
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    That looks like a Shimano BB and crank. You require a splined cup tool: Shimano TL-UN74-S

    All the major bike tool makers have a compatible tool available as well.

    The spindle length is dependent on the model crank to be used. So, if you buy Crank X, it'll require BB Y for an English spec BB shell. Or BB Z for an Italian spec BB shell. etc.

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