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recently the crank arms on my Nishiki Colorado Comp 27.5 bike failed. I must’ve struck an obstacle with my pedals during my ride yesterday, because on the way home I noticed the right pedal was bent and when I removed it the threads were torn up. I installed this pedal myself; I confirmed it went in with the correct thread direction, though I settled on hand tightening.

So obviously I need a new crank of about 8” (200mm) and with 4 bolts. But I’m not sure how to find the proper crank, nor how to avoid this crank destruction in the future.

  • I’d just like to comment that it’s really strange that the pedal became bent. I rode my old bike for much longer and have endured many more strikes and have NEVER damaged a crank this bad. Must have been faulty installation procedure? – jay w Nov 20 '18 at 1:16
  • A picture of left crank would be useful. If you can remove the bolt that fixes the crank to bottom bracket, picture of what is underneath could be useful too. Crank length is measured from center of pedal hole to center of fixing bolt hole, usually it is something between 170 and 180 mm. – ojs Nov 20 '18 at 1:20
  • Ok. I can make that happen in a few hours. I’m also contemplating buying a new crankset or using one from my other bike. – jay w Nov 20 '18 at 1:30
  • If some of the thread remains you could try re-cutting it. – Michael Nov 20 '18 at 8:10
  • It’s completely destroyed unfortunately. – jay w Nov 20 '18 at 17:13
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To find a replacement, there are a few details that you need to get from your current crankset. The most important one is to find what the bottom bracket of your bike is. You may need to remove the crank arms to work this out.

Next, you need to know the bcd of the chainring to ensure that it will fit on your replacement crankset. Also verify that the four bolts are evenly spaced on the chainring, as some brands like Shimano change their bolt spacing in a way that is only compatible with Shimano cranksets or a select few third party cranksets designed to take Shimano chainrings.

Lastly, purely for bike fit reasons, you'll want to ensure that the replacement crank arms are the same length. While the arm of your current crankset might be 200 mm, that is not the measurement that you need for this. To measure crank length, you need to measure the outside of the crank arm from the centre of the spindle to the centre of the hole for the pedal. This measurement should be between 170 and 175 mm on almost all standard bikes.

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  • So maybe I’d be better to replace the crank set entirely, since it only requires a measurement of the bottom bracket. – jay w Nov 20 '18 at 2:48
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    often enough the measurement is stamped on the inner face of the cranks. – Swifty Nov 20 '18 at 6:50
  • There's a chicken and egg problem, you need to know the bottom bracket type to know how to remove the cranks – ojs Nov 20 '18 at 11:47
  • CW175 is stamped on the arms. So this could be the length of the crank arms in mm? – jay w Nov 20 '18 at 17:11
  • If your bike frame size is large or XL, then it's likely to come specced with 175mm cranks. If you are less than 6'/180 cm tall, then you might want shorter cranks than that. – Carbon side up Nov 21 '18 at 6:14
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Replace the entire crankset (both crank arms, and possibly the chainring too). You'll have a hard time finding a matching right side arm.

From the photos I can see you have a '3 piece' crankset where the axle is fixed in the bottom bracket and is separate from the cranks (the bolt in the crank arm shows this). There are a few crank-axle interface types: square taper, and a few splined - 'Octalink', 'Powerspline' and 'ISIS' types. You'll need to find out which one you have.

It's quite likely the interface type is square taper, if you remove the central bolt and washer, you should be able to see the end of the axle. If it's square you have a square taper crank.

To find a replacement you will also need to know the length of the crank arm from bottom bracket axle center to pedal axle center. These come in 2.5mm increments, 'default' size on a MTB is 172.5 or 175mm.

If you want to use you existing chainring ring you'll need the chainring bolt circle diameter (BCD) and pattern - yours look evenly spaced, some have pairs of bolts closer together. Or, you can get a crankset with a new chainring, in which case you just need one with a chainring with the same number of teeth.

Replacing square taper cranks is not a hard job, but does require a special tool to pull the cranks off the bottom bracket axle. Also, the new cranks should be tightened onto the axle with a torque wrench to ensure sufficient torque is applied (but they are not over-torqued). You do not want the alloy cranks to loosen on the steel axle as this can ruin the square hole in the crank in short order.

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  • There are many types of cranks that have a bolt in the middle, not just square taper. Octalink (V1 and V2) , Powerspline, and ISIS are the other ones that I'm aware of, but there may be others. – Kibbee Nov 20 '18 at 14:06
  • @Kibbee, you're right. I should not answer questions early in the morning. – Argenti Apparatus Nov 20 '18 at 14:14

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