PDA

View Full Version : Could it be a bent crank arm....



Terpfan
01-16-2014, 08:59 AM
Quick background, riding this past weekend I took a little fall on one of those nice wet wooden bridges just before Mt. Vernon on the MVT (last little bridge at the bottom of the big hill before it). The bike and I went down at almost a 90 degree angle so my right pedal area hit the wood. It bent the metal on the pedal back and popped the chain off. I was able to pop the chain back on, derailer seemed fine and ride with half a pedal back to Spokes on Belle View. As I rode it, my right leg (side that went down) with half a pedal would feel like I was making somewhat of a mini s curve with my shoe each time I did one rotation. I explained what happened and dropped it off for a tuneup and new pedals.

Fast forward to last night, picked it up with my wife on the way home from a post-work event. Didn't ride it up the hill in a suit so tossed it in the back of the car. This morning, I rode in. Of course brakes, gears, etc feel great from tuneup, but even with new pedals, I still have a little bit of that s curve feeling on the right side. I think maybe the crank arm is bent, but when I eyeball it, everything looks fine. It's definitely far less pronounced than it was when I rode it right after falling over top there (i'd say 75% better), but it still persists. So my question is one, is it likely the crank arm? And if, not, what other possibilities exist? And two, is this something I can easily fix myself or do I need to get new crankarm and go back to shop?

mstone
01-16-2014, 09:23 AM
I wouldn't expect a bent arm to go back and forth, that sounds more like a bent crank (the part that goes through) or misaligned bottom bracket. Not easy or cheap if that's the case, as it means a new crank assembly and/or bottom bracket. FWIW, a bent arm would probably mean the same thing anyway, that's not a part I'd bend back and ever trust again.

Terpfan
01-16-2014, 11:13 AM
I wouldn't expect a bent arm to go back and forth, that sounds more like a bent crank (the part that goes through) or misaligned bottom bracket. Not easy or cheap if that's the case, as it means a new crank assembly and/or bottom bracket. FWIW, a bent arm would probably mean the same thing anyway, that's not a part I'd bend back and ever trust again.

Thanks!

Figures about as much that it's something down there and that it would be expensive :(. I have a thought on repair that may help reduce cost that i'm exploring. And now I have even more motivation to try to elevate myself to N+1 status.

hozn
01-16-2014, 11:26 AM
Thanks!

Figures about as much that it's something down there and that it would be expensive :(. I have a thought on repair that may help reduce cost that i'm exploring. And now I have even more motivation to try to elevate myself to N+1 status.

While these repairs aren't cheap, it doesn't have to be crazy expensive either. More details needed on what you currently have in terms of crankset/bottom bracket (double or triple? threaded, English [not Italian] - aka "BSA" - I assume?), but people ditch cranksets frequently on Craigslist. A decent used Sram or Shimano crankset would probably be in the $50-70 range. That may include a bottom bracket, but if not, you can get a new external BB for somewhere in the $25-35 range. And if you go with an older ISIS or square taper BB (and compatible cranks, obviously) probably cheaper.

Just search CL for "crankset"; there are a bunch out there. Some are fairly fancy/more expensive, but the estimates above look about right for the others.

Edit: oh, and while there is risk in buying something that won't work on your bike (hence wanting to understand what you have now), you are welcome to bring it by and use my tools/help to get the new one installed.

KLizotte
01-16-2014, 02:56 PM
Quick background, riding this past weekend I took a little fall on one of those nice wet wooden bridges just before Mt. Vernon on the MVT (last little bridge at the bottom of the big hill before it). The bike and I went down at almost a 90 degree angle so my right pedal area hit the wood. It bent the metal on the pedal back and popped the chain off. I was able to pop the chain back on, derailer seemed fine and ride with half a pedal back to Spokes on Belle View.

I feel your pain. That has got to be one of the worse bridges on the MVT as evidenced by all the skid marks into the fencing heading south. A couple of summers ago I slid into the fencing and went down really hard on my right side too. Broke my thumb, gave myself a black eye, and some lovely wood rash. It is very, very slippery all year round because it gets so little sun and mildew builds up. I could see my pedal's gouge out for a good year before it began to fade into the rest of the wood.

You all have been warned!

Vicegrip
01-16-2014, 08:46 PM
i would think a bent BB on the right side would be visable by looking at the chain rings for a wobble. To check the arm for an out of true that is not visable in motion you could firmly clamp the bike in a stand and measure the level across the pedals. Clock the crank 90 deg and check again. If a crank arm or pedal shaft is bent the measurements will diverge. I have the shop space and equipment to check this if you want.

They need to do something with that wood bridge. It is covered in splat scars. How many people have to get hurt there before they install a non slip surface on atleast that one bridge?

mstone
01-17-2014, 06:09 AM
They need to do something with that wood bridge. It is covered in splat scars. How many people have to get hurt there before they install a non slip surface on atleast that one bridge?

They can't do that, because (except for all the highways), nature.

cyclingfool
01-17-2014, 10:00 AM
They leave it slick so people can ski on it. :rolleyes:

Terpfan
01-22-2014, 10:22 AM
While these repairs aren't cheap, it doesn't have to be crazy expensive either. More details needed on what you currently have in terms of crankset/bottom bracket (double or triple? threaded, English [not Italian] - aka "BSA" - I assume?), but people ditch cranksets frequently on Craigslist. A decent used Sram or Shimano crankset would probably be in the $50-70 range. That may include a bottom bracket, but if not, you can get a new external BB for somewhere in the $25-35 range. And if you go with an older ISIS or square taper BB (and compatible cranks, obviously) probably cheaper.

Just search CL for "crankset"; there are a bunch out there. Some are fairly fancy/more expensive, but the estimates above look about right for the others.

Edit: oh, and while there is risk in buying something that won't work on your bike (hence wanting to understand what you have now), you are welcome to bring it by and use my tools/help to get the new one installed.

It's a cannondale quick 4. I don't have any fancy road bikes (yet). Thank you for the offer. I've been riding on it, sans today, and it actually hasn't been too bad. I think it's slowly seemingly warping itself back or i'm just not noticing it as much.

Terpfan
01-22-2014, 10:25 AM
i would think a bent BB on the right side would be visable by looking at the chain rings for a wobble. To check the arm for an out of true that is not visable in motion you could firmly clamp the bike in a stand and measure the level across the pedals. Clock the crank 90 deg and check again. If a crank arm or pedal shaft is bent the measurements will diverge. I have the shop space and equipment to check this if you want.

They need to do something with that wood bridge. It is covered in splat scars. How many people have to get hurt there before they install a non slip surface on atleast that one bridge?

Thanks, once it warms up, i will try to do a check. I don't have a bike stand, but can put it up onto my work bench and probably clamp in place to check. Or at least i will try it.

As for the bridge, I wonder if it would be considered vandalism if it suddenly appeared on the bridge one morning? I feel like it may save some more broken fingers, broken bikes, and possible worse injuries down the road.