Bent Crankset?

DaveyDave

I think I have a bent crankset. It seems that when I pedal, at a certain part of the stroke the crankset is bent outward causing the chain to rub off the front derailleur. It seems to have gotten noticeably worse recently, when I look down as I pedal I really notice it moving outward at a certain part of the pedal stroke, the other week it was just a slight bend.

This is on a Lapierre Tecnic 300, used on roads and there hasn't been any bangs or crashes that would cause damage to it.

I know I should get it sorted asap but I'm doing my Leaving Cert right now and don't finish until Wednesday. I was hoping to hold off until my next service which is in about 400km. What kind of damage am I looking at here, can it be repaired or will I need a new crankset? Hopefully it's not too costly...

adrianshanahan

Get it sorted ASAP,

This prob be going down the replacement route, get one of these drop into James In OC Tuning with it and he will lash it on have you in tip top shape for pocket change.

Adrian

doozerie

If the crank/spider is bent then yes you will need to replace it. The fact that it seems to have gotten worse over the course of a week or two makes me wonder whether it really is bent though as whatever about how it got bent in the first place I can't see how it would deteriorate even further so rapidly. I've had a bent spider once and believe it happened when a car reversed into my bike while it was parked, I'm struggling to think of how else yours might have been damaged other than a serious knock.

So before you go any further I would investigate the crank for something other than a bent spider. The only thing that springs immediately to mind is that maybe a chainring bolt is loose and allowing the chainring(s) to flex when pedalling - try tightening the chainring bolts. Also check for any signs of play between the crank and the axle it is attached to.

seamus

Spider is very difficult to bend. Especially on modern alloy chainsets, it doesn't bend, it will just snap if struck hard.

More than likely your chainring has bent or become warped, this is why it moves outward at the same spot every time.

Occurs most frequently when you drop the bike, hit a rock, or someone throws their bike against yours, their pedal banging off the chainring. If it's been getting worse, then doozerie may be onto something with the missing chainring bolt.

Easiest way to diagnose it is to remove the chainring and place it on the ground. It should be flat or almost.

Replacement takes ten minutes and can be done by any bike shop.

DaveyDave

This morning I noticed a slight clicking while pedaling, again it was at a certain part of the crank rotation, I don't recall feeling any disruption when it clicked, but could hear it. It wasn't a problem when I used less force. the whole drive side crankset seems to be at an angle like this / except not as extreme.

I took the big chainring off, it's flat. I left the other two on and they're also moving outward, so I'm guessing it's something to do with the bottom bracket?

Whatever it is, I'm not in the position to get it fixed this weekend, and I have to ride with it until Wednesday.