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  1. #1
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    Breaking Cranks...Help Please!

    Hello,
    I'm new to mountain biking I bought a K2 Shadow Nine mtb on black friday 11/22/12 because I wanted to get in shape and I was on a budget. I started riding it everyday around Jan 5 2013 and after about two weeks i stripped the stock crank arm on the side opposite the sprocket it was splined. I took it back to the store where I bought it and they said it was a defect and the bike came with a 1 year warranty so they would fix it no charge. The crank they replaced it with is a SR Suntour XCT and after about a week on riding it it keeps coming loose on the same side and wont stay tight after only minutes of riding...I'm not sure what to do. it is a sqaure style mount not flanged I'm not sure which is better.

    I'm a big clyde I was 308 LBS when I started riding and am currently at 295 and i'm 6'3" tall. Should I get a chromoly crank? I used to ride bmx when I was youner so I stand to pedal a lot is that breaking them? I'm wondering because I stand a lot and am a big guy if a DJ bike would be stouter and hold up to me better?

    Any help/ Advice is apperciated...

    Adam

  2. #2
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    I would think this is an equipment problem. I was 350+ a couple years ago and have never had this problem. If your hardware is tightened to MFG spec's then you may want to look into a better quality crank...

  3. #3
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    Hi Adam,

    What you are describing is a problem with the crank bolt not being tightened to the correct spec when it was installed and assembled. The bolts need to be set at 45-50nm in order for the crank to stay put.

    That being said, because the arm is aluminum and the spindle in most cases is hardened steel the aluminum will fatigue to a point that the taper becomes out of spec and the crankset needs to be replaced if the bolt becomes loose and it is ridden on for any period of time.

    Nick
    SR Suntour warranty/technical advisor

  4. #4
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    Over 300, I'd recomend an external BB carnkset. They have much bigger axles and wider spaced bearings for strength and sitffness. About the cheapest option available is listed below.

    BlueSkyCycling.com - Race Face Ride XC X Type Crankset w/ Bottom Bracket

    That Suntour crank is a square taper which don't have strong enough axles for big guys. I brok a few axles before upgrading to an external BB crank.

  5. #5
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    Quote Originally Posted by Sasquatch1413 View Post
    Over 300, I'd recomend an external BB carnkset. They have much bigger axles and wider spaced bearings for strength and sitffness. About the cheapest option available is listed below.

    BlueSkyCycling.com - Race Face Ride XC X Type Crankset w/ Bottom Bracket

    That Suntour crank is a square taper which don't have strong enough axles for big guys. I brok a few axles before upgrading to an external BB crank.
    I used this crankset at 265# and had no problems, still going strong. It's actually pretty good for the money. Just make sure its installed and torqued properly.

  6. #6
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    Thanks for the replies guys. I am going to take the bike back where I got it after work today and see if they will do anything because the bike is still supposed to be under warranty. If I don't get anywhere with that I will probably purchase the suggested crank. Just curious what does external BB mean in terms of cranks? like I said I'm new to biking, just trying to expand my knowledge base thanks.

  7. #7
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  8. #8
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    the store I bought it at (sports Authority) told me because of my size they were worried I was going to continue to break the bike so they allowed to return it for a full refund. I picked up a used XL Kona Scrap on craigslist and am having way more fun.

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