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Help request from a bike DIY noob

DirkgentlyDirkgently Posts: 14
edited May 2013 in MTB workshop & tech
Ok, I will start this call for help by mentioning that I know next to nothing about bike mechanics. I am sure that you would have arrived at this conclusion for yourselves by the end, but I thought I would get in first and save you the time :)

I have recently bought (on advice from here) a Rockrider 5.3 from Decathlon, I have no issues with it at all and think it was a great purchase. The bike was bought to replace an older bike that I had effectively run into the ground - a Carrera Vulcan from Halfords. I thought that I might be able to learn my way around the bike by trying to rejuvenate the old bike and get it to a rideable state again.

I am working through the problems one by one and have come to one where I am not really sure how to proceed. The left hand (crank?) wobbles fairly significantly, both forward and back and then more recently side to side. This has been an ongoing issue which was initially fixed simply by tightening the allen key bolt on the end of said crank. Once this stopped working, the issue became more and more severe and eventually made the bike unrideable.

I have taken the crank off the bike and found the inside of the square hole had been almost completely rounded off although the square "peg" coming out of the (bottom bracket?) seems to be in good condition.

My main question is, do I need to replace both cranks (as this would also seem to include the 3 front gear system) or can I just replace the damaged one. If I can replace just the one crank, do I need to get the exact same type to replace it and if so, how do I find out which it is?

Finally, whether I need 1 crank or the whole set, is there anywhere you would recommend that I buy them from?

Thanks in advance!

The crank-set has "SR Suntour PFF" printed on it and it is not the original set that cam with the bike. Hope that means something to someone!


  • nicklousenicklouse Posts: 50,675 Lives Here
    single cranks can sometimes be found in good bike shops that actually service stuff.

    not new but they might have one.

    or new crankset if the BB is in good condition.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
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  • cooldadcooldad Posts: 32,599
    You can often find odd cranks on Ebay, I might even have one lying around. You need to check the crank length - will be stamped on somewhere, and whether it's Shimano, Truvativ or Sram compatible. I seem to think from fiddling around that the square holes are 90? degrees apart on one of them. So if you look at the crank vertically the hole will either look square or diamond shape
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  • DirkgentlyDirkgently Posts: 14
    The hole looks square rather than diamond and all I can find printed on the crank is "Suntour, Taiwan, 870, 2"
  • WindyGWindyG Posts: 1,099
    can you take a pic of what you have, I have a load of stuff here ready for to go for scrap and I might have one.
    If I have you can have it for the cost of postage.
  • The RookieThe Rookie Posts: 27,804
    Measure the distanec between the hole centres, that is crank length, I'm pretty sure I have a spare 170mm Shimano/Suntour compatable crank.

    The axle will be perfect, it's hardened steel and the alloy crank arm doesn't put up much of a fight!
    Current steed - Whyte T129, 2013 frame, mongrel Revelations, Giant dropper, Stans S1 wheelset. 12, Magura Trail Sport brakes, 1x11. 12.8Kg
  • DirkgentlyDirkgently Posts: 14
    I reckon the distance between the centre of each hole is 178mm. I have a few JPGs if that would help but have no idea how to attach them to this post. Would it help at all if I listed the gear set?
  • The RookieThe Rookie Posts: 27,804
    It will be 170 or 175mm, so probably 175mm!other than length you don't need a visually matching crank for anything but aesthetics.

    Familiar with the PFF's as my wife has them on hers.
    Current steed - Whyte T129, 2013 frame, mongrel Revelations, Giant dropper, Stans S1 wheelset. 12, Magura Trail Sport brakes, 1x11. 12.8Kg
  • DirkgentlyDirkgently Posts: 14
    I've ordered a 175mm suntour one from amazon. Not expecting miracles since it was only £12, but if it works I'll be very happy. Thanks for the helpful information. I'll update this thread when the item arrives and I get chance to try it.
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