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  1. #1
    Dirt Bomb sknhgy's Avatar
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    Buying a crankset

    I need a crankset for my beater bike. It is a low end Trek 820. It is a 7 speed. I don't want to sink a lot of money into it. My question is, will this:

    http://www.bikepartsusa.com/bikepart...rank-crank_mtn

    Be a good replacement for this:

    IMG_0321 (1024x768) (640x480).jpg?

    The worn out crank has 28/38/48 chainrings and 175mm cranks. It is riveted together. The problem with the new one is there is no information. I don't know the ring or crank sizes. But as long as they would work it really doesn't matter. I think a 170mm crank would work.

    OR

    Could someone suggest a crankset that is a little better? The next best one I could find is about $60. I would get that if I had to, but if the $16 one would work I'll go with it.

    Thanks in advance.
    Last edited by sknhgy; 04-06-13 at 10:57 AM.
    more cops have been killed by donuts than guns in chicago it is a medical fact ask any doctor.

  2. #2
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    I think those Pyramid ones are 42/34/28 if it's the on I think it is from this page. If it's the other one, then it's 48/38/28.

    A cheap'n'cheerful Shimano Tourney triple like the one below you can get for around $30 US.

  3. #3
    Senior Member Bill Kapaun's Avatar
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    You'll probably have to change the BB too. it seems the newer cranks use shorter spindles than the older ones.

    Are you really sure your crank is worn out? Compare the teeth to a new crank before you condemn it. Not all teeth have the same profile. Some are different to assist shifting.

  4. #4
    coprolite fietsbob's Avatar
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    You'll probably have to change the BB too. it seems the newer cranks use shorter spindles than the older ones.
    ... or at least be aware that when you buy a new crank, with replaceable chainrings, this time,
    might as well get the BB,too, length, as recommended be used with that particular Crank-set..

  5. #5
    Dirt Bomb sknhgy's Avatar
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    Quote Originally Posted by Continuity View Post
    I think those Pyramid ones are 42/34/28 if it's the on I think it is from this page. If it's the other one, then it's 48/38/28.

    A cheap'n'cheerful Shimano Tourney triple like the one below you can get for around $30 US.
    Where would I get one of those Shimanos?

    I'm pretty sure the middle ring is worn. I just replaced the chain, cassette, and RD, and now the chain jumps badly when I ride the middle ring - which is the one I use 99% of the time.
    The bike is about 10 years old and has seen much use.
    more cops have been killed by donuts than guns in chicago it is a medical fact ask any doctor.

  6. #6
    coprolite fietsbob's Avatar
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    Distributors To bike Shops will have access them , check with your LBS ..

  7. #7
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    You can get them on Amazon, Ebay quite easily and cheaply, too, but be warned that you're on your own fitting them, and will have to have the tools to do so (which are quite cheap and handy to have around if you own a bike or many).

    For interest's sake, it would be good if you could post an image of your chainring(s), esp. the middle one.

    New BBs can be had starting at around $10 or so for a basic square taper one, like a Shimano UN-26 - you have to ensure that you get the correct spindle length.

    If y

  8. #8
    Dirt Bomb sknhgy's Avatar
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    Quote Originally Posted by Continuity View Post
    You can get them on Amazon, Ebay quite easily and cheaply, too, but be warned that you're on your own fitting them, and will have to have the tools to do so (which are quite cheap and handy to have around if you own a bike or many).

    For interest's sake, it would be good if you could post an image of your chainring(s), esp. the middle one.

    New BBs can be had starting at around $10 or so for a basic square taper one, like a Shimano UN-26 - you have to ensure that you get the correct spindle length.

    If y
    My op has a pic.
    I just want a crank to replace the worn original one. That is all. Thanks.
    more cops have been killed by donuts than guns in chicago it is a medical fact ask any doctor.

  9. #9
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    Quote Originally Posted by sknhgy View Post
    My op has a pic. I just want a crank to replace the worn original one....
    I meant a close-up of the teeth to see if they were so worn as to actually need replacing.

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    Quote Originally Posted by sknhgy View Post
    My op has a pic.
    I just want a crank to replace the worn original one. That is all. Thanks.
    The problem is that the BB and crankset need to "match" in terms of spindle length (at least to some degree). Otherwise, your crank may bottom out against the frame before it is tightened onto the square taper. If it's wrong to a smaller degree, your chainline will just be weird - forcing you to favor certain gear combinations over others.

  11. #11
    Senior Member clasher's Avatar
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    Shimano alivio starts at 24 according to the website, and a new BB shouldn't be more than 20. I think that listing shows what length spindle to get too so you can measure your current one to see if it'll work or not... if it spins smooth I'd just leave it alone. Based only on that picture and the skipping you're experiencing it's almost certain that your rings are worn.

  12. #12
    Dirt Bomb sknhgy's Avatar
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    I should be able to do this. I can measure the chainline and I have the tools to pull the cranks and to take out the bb. I dont do this everyday so I need to ask questions and look things up. If I take every little thing to the lbs I'll go broke.
    more cops have been killed by donuts than guns in chicago it is a medical fact ask any doctor.

  13. #13
    S'Cruzer pierce's Avatar
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    I do prefer the UN55 BBs over the UN26s, they are smoother, and the metal lock ring always feels better when I torque it on (and it comes off cleanly without cracking). they are probably $5 or $10 more than the UN26's.

    the tourney cranks are pretty heavy and kind of clunky, the alivio is a decent notch better. you gotta spend a chunk more to get anything much nicer (deore or whatever around $100).

  14. #14
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    I've got a UN26 that I was thinking of using if it's the right length for some nice vintage White Industries cranks to put on my old Marin to replace the UN72(?) that's been on there since I got the bike in 1992 (!).

    I've got a metal lockring to put in place of the plastic one on the UN26 - is that what you've had experience of cracking on them?

    I also noticed that the UN26 seems to use cartridge bearings pressed into the ends of the metal shell, as opposed to the more 'all in one' look of other UNs I've seen.

  15. #15
    Senior Member BentLink's Avatar
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    How about just changing the worn middle ring?
    You can find some at Niagara for example.
    I'm more "Shrek" than "Schleck"

  16. #16
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    Quote Originally Posted by BentLink View Post
    How about just changing the worn middle ring?
    You can find some at Niagara for example.
    Afraid not -

    Quote Originally Posted by sknhgy View Post

    The worn out crank has 28/38/48 chainrings and 175mm cranks. It is riveted together.

  17. #17
    Dirt Bomb sknhgy's Avatar
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    Will I notice much difference if I switch from a 175mm to 170mm crankarms?
    Will there be much difference if I go with 22/32/42 teeth as opposed to the original 28/38/48?
    I'm thinking this would be a good idea because I run skinny tires and the pedals are very close to the ground with the 175's.

    Thanks everyone.
    Last edited by sknhgy; 04-07-13 at 08:57 AM.
    more cops have been killed by donuts than guns in chicago it is a medical fact ask any doctor.

  18. #18
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    It would help prevent pedal strike a *tiny* amount (5mm ), and lower your pedalling torque by an equally tiny amount - how tall are you?

  19. #19
    Dirt Bomb sknhgy's Avatar
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    Quote Originally Posted by Continuity View Post
    It would help prevent pedal strike a *tiny* amount (5mm ), and lower your pedalling torque by an equally tiny amount - how tall are you?
    I'm short and stocky and I put out a lot of torque.
    more cops have been killed by donuts than guns in chicago it is a medical fact ask any doctor.

  20. #20
    Senior Member Bill Kapaun's Avatar
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    IF you're short, you may be able to spin a lower gear faster, ending up with a higher speed overall.
    I have a bad knee and going shorter made a remarkable difference for me. Don't forget to raise the seat 5mm.

    I'd replace with the same tooth counts to avoid any FDER issues.

  21. #21
    S'Cruzer pierce's Avatar
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    note that on a bicycle you don't WANT to 'put out a lot of torque', rather you want to spin faster in a lower gear. mashing hard on the pedals is a sure way to trash the bike *and* your knees in the long run.

  22. #22
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    You may benefit from installing even shorter crankarms, maybe 165mm if you can find them, and learning to spin faster.

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