Why do my brand new chainsets look buckled?

Ask for advice or share your fettling tips
PenguinWithHair
Posts: 166
Joined: Wed Dec 02, 2009 15:00 pm

Why do my brand new chainsets look buckled?

Postby PenguinWithHair » Tue Oct 02, 2012 22:10 pm

Hey everyone, I've installed three different chainsets on my bike now (Singlespeed road bike) and every time the chainrings don't look perfectly true. It's difficult to say exactly but from what I can see it looks like the entire half opposite the crank moves inwards towards the frame by 1 or 2mm. I've installed new bottom brackets each time too. It's my everyday bike which I'm fairly reliant on which runs a big old 1/8th chain. I can tell you it's a fairly modern steel frame too. So here's my questions...

Can anyone speculate why this is happening?
Could it be an error in my instillation?
Is it often the case chainrings/crankarms just aren't perfect?
Could it in fact be my frame which is slightly out of shape?
Is it really that much of a big deal?

Many thanks!

PenguinWithHair
Posts: 166
Joined: Wed Dec 02, 2009 15:00 pm

Re: Why do my brand new chainsets look buckled?

Postby PenguinWithHair » Tue Oct 02, 2012 22:12 pm

My apologies but one more question!

How can you tell if a chainring and/or crank arm is out of shape without spinning it while having it installed on a bike?

DesWeller
Posts: 5233
Joined: Mon May 05, 2008 15:36 pm

Re: Why do my brand new chainsets look buckled?

Postby DesWeller » Tue Oct 02, 2012 23:49 pm

Remove the chainring and lay it on a a flat surface. Unlikely to be a bent crankshaft or spider - they are pretty strong.

User avatar
smidsy
Posts: 5256
Joined: Tue Jan 17, 2012 20:52 pm

Re: Why do my brand new chainsets look buckled?

Postby smidsy » Wed Oct 03, 2012 05:36 am

Do they look OK before you fit?

If so the frame could be the thing that is bent.
Yellow is the new Black.

User avatar
Me-109
Posts: 1045
Joined: Wed Jul 25, 2007 15:39 pm

Re: Why do my brand new chainsets look buckled?

Postby Me-109 » Wed Oct 03, 2012 12:00 pm

PenguinWithHair wrote:It's difficult to say exactly but from what I can see it looks like the entire half opposite the crank moves inwards towards the frame by 1 or 2mm.

So does it look like that or is it actually like that? It could just be an optical illusion brought about by the shape of the crank arms. Try holding a pencil or rule against the frame with the end just to the inside of the outer chainring, then turn the cranks slowly. Does the inside of the chainring move closer to or away from the pencil (or other)? By how much? Repeat for other rings if you wish.

lpretro1
Posts: 211
Joined: Fri Apr 02, 2010 13:47 pm

Re: Why do my brand new chainsets look buckled?

Postby lpretro1 » Wed Oct 03, 2012 12:49 pm

Remember also that some of the teeth are shaped to assist smoother chain take up so when you look at it it won't look entirely round as you rotate the cranks.

User avatar
ALIHISGREAT
Posts: 3918
Joined: Tue Aug 02, 2011 15:43 pm

Re: Why do my brand new chainsets look buckled?

Postby ALIHISGREAT » Wed Oct 03, 2012 16:19 pm

lpretro1 wrote:Remember also that some of the teeth are shaped to assist smoother chain take up so when you look at it it won't look entirely round as you rotate the cranks.


That's what I was going to say :(

User avatar
k-dog
Posts: 1432
Joined: Thu Sep 28, 2006 13:49 pm

Re: Why do my brand new chainsets look buckled?

Postby k-dog » Wed Oct 03, 2012 23:46 pm

A single speed shouldn't have different tooth profiles - they're only there for shifting.

I would definitely do the pencil thing and see if it is actually warped. The most likely thing is that it's just not seated on the spider evenly. Sheldon Brown has a method for sorting that - loosening the bolts a bit and then tapping them.
I'm left handed, if that matters.

User avatar
nicklouse
Lives Here
Posts: 80713
Joined: Thu Mar 20, 2003 12:14 pm

Re: Why do my brand new chainsets look buckled?

Postby nicklouse » Thu Oct 04, 2012 00:02 am

what rings are you trying?

and do you have pics?

and when you spin the crank does the ring run true or how much does it move?
"Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
Parktools :?:SheldonBrown

User avatar
NapoleonD
Posts: 18126
Joined: Sat Oct 08, 2011 19:51 pm

Re: Why do my brand new chainsets look buckled?

Postby NapoleonD » Thu Oct 04, 2012 06:55 am

It's not the frame flexing under power is it?
Twitter - @NapD
Strava - Dense Voigt

User avatar
ju5t1n
Posts: 1936
Joined: Tue Sep 09, 2003 09:45 am
Contact:

Re: Why do my brand new chainsets look buckled?

Postby ju5t1n » Thu Oct 04, 2012 20:07 pm

NapoleonD wrote:It's not the frame flexing under power is it?

This would be my guess

User avatar
k-dog
Posts: 1432
Joined: Thu Sep 28, 2006 13:49 pm

Re: Why do my brand new chainsets look buckled?

Postby k-dog » Thu Oct 04, 2012 20:26 pm

^ that's the wrong way if I read it right - he says it looks closer opposite the crank but if it was flexing it would move out.
I'm left handed, if that matters.

User avatar
ju5t1n
Posts: 1936
Joined: Tue Sep 09, 2003 09:45 am
Contact:

Re: Why do my brand new chainsets look buckled?

Postby ju5t1n » Thu Oct 04, 2012 20:33 pm

Pressure on left crank could cause BB flex and move the chainring towards the frame

User avatar
ju5t1n
Posts: 1936
Joined: Tue Sep 09, 2003 09:45 am
Contact:

Re: Why do my brand new chainsets look buckled?

Postby ju5t1n » Thu Oct 04, 2012 20:37 pm

This used to happen on a 653 frame I had years ago, I too thought the chainrings were the problem at first. But it was just a shit frame

PenguinWithHair
Posts: 166
Joined: Wed Dec 02, 2009 15:00 pm

Re: Why do my brand new chainsets look buckled?

Postby PenguinWithHair » Sat Oct 06, 2012 07:52 am

Hey everyone, thanks for all the input folks! I can however rule out a few possibilities.

It's not a load/stress dependent issue as it was visible upon first instillation.
I don't think it's to do with the design for shifting assistance as I'm running single speed chainrings.

My personal speculation has narrowed to the frame being out of shape, or the chainrings not quite sitting perfectly on the crank, I only discovered that was actually a thing that can happen reading from here. It's a 520 frame so it's basically, alright but not the best..?

I shall report back with pictures and results from a 'pencil test' : )

In the meantime I'm going to also conclude it's not really buckled enough for it to be an issue, I posted this here out of curiosity more than anything.


Return to “Workshop”

Who is online

Users browsing this forum: No registered users and 4 guests