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-   -   Replacing a left crank- finding an equivalent part? (http://www.bikeforums.net/bicycle-mechanics/935945-replacing-left-crank-finding-equivalent-part.html)

tiffle 02-27-14 09:47 AM

Replacing a left crank- finding an equivalent part?
 
Hi there. First-time poster here. Pretty new to bicycle maintenance as well.

I have a 20" Schwinn Hinge that I use to commute to school every day, about three miles one way. Recently the pedal on the left crank was bent down in the crank's socket (still not sure how this happened!) and I had to unscrew it and screw it back in very carefully to make it fit back in straight. It's slowly bending out of place again so I know I'm going to have to replace the arm before I have a catastrophic failure. Don't want to have to take the bus on short notice, haha.

I tried searching for a guide on how to find a replacement part for this, but had no luck. How do I know what kind of crank to buy? Specifically, the specifications so it matches the rest of the crankset. I linked to the specs of the bike earlier in my post, but it's not specific about what the sizes are.

Any ideas? I'm only looking to replace the crank itself for now until I can get a new crankset.

Homebrew01 02-27-14 10:51 AM

I can't tell what type of bottom bracket it has. If it is the older, but common "square taper", then it may not be too hard to find a replacement left arm, that will fit, even if a different brand. You need to measure from the center of the pedal axle to the center of the crank axle to get the length. Common sizes are 165mm, 170mm, 172.5 mm, but a bike like yours may have a less common smaller size.

HillRider 02-27-14 10:59 AM

Looking at the link you posted, it seems to have a square taper bottom bracket and a replacement arm should be easy enough to find. The back of your current crank should have a number indicating its length, 165, 170, etc on it and you want to match that length. Also square taper crank arms come with the square oriented so the side are parallel to length of the crank OR at 45 so they look like a diamond. You must get the matching orientation. I'd take the bike to a decent bike shop or co-op and see what they have in their salvaged parts bins. The shop personnel can help you get the proper length and orientation match

CACycling 02-27-14 11:05 AM

Can also look at having a Helicoil put in at a LBS. Depending on how badly the threads are damaged, it may be an option.

tiffle 02-27-14 01:15 PM

Thank you all!

Regarding the sort of bracket, is there a way for me to tell without having to first remove a crank? I don't have the tools for that- was lucky to have a wrench to fix the pedal. I'm thinking I may have to contact the manufacturer to find out.
Quote:

Originally Posted by CACycling (Post 16532176)
Can also look at having a Helicoil put in at a LBS. Depending on how badly the threads are damaged, it may be an option.

I considered this, but decided a new part would be best.

CACycling 02-27-14 01:20 PM

Quote:

Originally Posted by tiffle (Post 16532601)
Regarding the sort of bracket, is there a way for me to tell without having to first remove a crank? I don't have the tools for that.

You should be able to tell by looking at the spindle at the back of the crank arm. This will also tell you the orientation of the square taper assuming that is what it is. Regarding the crank arm tool, you will need it eventually to remove and replace the arm so why not get that first?

HillRider 02-27-14 01:22 PM

A trip to a decent bike shop will tell you more and faster that attempting to contact Schwinn or the crank maker.

cny-bikeman 02-27-14 01:50 PM

Quote:

Originally Posted by tiffle (Post 16532601)
I considered this, but decided a new part would be best.

On what basis? The Helicoil repair is stronger than original, maintains the original appearance, eliminates the need to find a crank arm that is the same length and style and costs less.

Crankycrank 02-27-14 11:58 PM

Quote:

Originally Posted by tiffle (Post 16531929)
Recently the pedal on the left crank was bent down in the crank's socket (still not sure how this happened!) and I had to unscrew it and screw it back in very carefully to make it fit back in straight. It's slowly bending out of place again so I know I'm going to have to replace the arm before I have a catastrophic failure.

Just noticed your bike has folding pedals. The pedal may just need some minor repair or could need replacement. Can you post a pic so we know what is exactly wrong here, it may not be the crankarm at all. Also where are you located. Some posters may be able to recommend some local help if they know where you're at.


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