Metallic rubbing sound

[magnatom]

My bike (Kinesis Tk road bike) seems to have developed a metallic sounding rubbing which occurs from the crank/bottom/bracket/front mech area of my bike. It only occurs when I am grinding hard, i.e. sometimes when I first push off, and when I am going up a hill and trying to put the power down. It happens as I put power through the crank and sometimes happens when I power through the left or right crank.

I've had a quick look and the font mech looks nice and centred, so I don't think it is that.

Any ideas about what it might be?

 

[magnatom]

Off the top of my head could be the rear tyre rubbing on the rear chainstay or the bearings are on the way out in the BB.

edit:reading again it looks to be the BB, have you checked if there is any play in the chainset.

It is possible that it isn't coming from the BB area. It can be difficult to localise a sound when your on the bike. Is it possible that the tyre would rub more when putting power down? I'll take a look at that.

I had the bike serviced just before I did my 100 mile ride, and I think the problem was probably there before this. It only happens once in a while, so it would be difficult for the LBS to replicate. They tightened everything up so I doubt if it would be play in the chainset...but I'll still have a look.

I'd also be surprised if the BB is the problem. I've only done about 850 miles on the bike. I'd be disappointed if the BB has gone that soon.

 

[PpPete]

Square taper cranks?
You can tighten the bolts on some of those up far beyond the recommended torque and B****ds still squeak when you put the power down.
Fortunately the Octalink on my best bike doesnt suffer from this(although I've heard they can) , but I have square taper on the hack that is otherwise good but squeaks when I'm grinding.... It's pissing me off but it will have to stay on there until I can pick up another fleabay bargain.

 

[tandemman]

It could also be a loose rear skewer or if the bike has machine made wheels the spoke tension could be too slack both of these lead to wheel distortion under load.

 

[Sh4rkyBloke]

Could just be pedals need a tad more grease... I've had it twice when there's a creaking which has been down to these buggers!

 

[ColinJ]

When making a really big effort on my steel-framed Basso I sometimes deflect the bottom bracket area of the bike enough for the chain to rub on the front derailleur cage. I reckon that might be your problem - your mighty legs are twisting your bike!

 

[magnatom]

When making a really big effort on my steel-framed Basso I sometimes deflect the bottom bracket area of the bike enough for the chain to rub on the front derailleur cage. I reckon that might be your problem - your mighty legs are twisting your bike!

I had wondered about this, as when I look down I can see that the chainrings do deflect a bit, but I'm not putting that much power down!

Thanks for the thoughts guys. Things to investigate...

In fact I wonder if I have got the sound on video, that might help with diagnosis...

 

[ColinJ]

I had wondered about this, as when I look down I can see that the chainrings do deflect a bit, but I'm not putting that much power down!

I find that it only happens in certain combinations of ring and sprocket which cause the chain to run very close to the derailleur cage so it doesn't take a big deflection for the chain to rub. That reminds me to trim the front derailleur position (Campagnolo ergoshifters allows this, I don't know if Shimano STI levers do).

 

[grhm]

When making a really big effort on my steel-framed Basso I sometimes deflect the bottom bracket area of the bike enough for the chain to rub on the front derailleur cage. I reckon that might be your problem - your mighty legs are twisting your bike!

I had wondered about this, as when I look down I can see that the chainrings do deflect a bit, but I'm not putting that much power down!
[/quote]

I get a little deflection that causes the chain to rub on the front mech when pushing hard in the big chainring and smallest sprocket. (and there's sufficient play in the system that I can remove it by pushing and holding the thumb shifter as if I want to select the non-existent cog after the smallest).

But it only happen swhen pushing down on the right crank - so I'd be supprised if this is your issue as you say it happens on both sides. The cage(?) on your front mech is probably wide enough that you'd need to put a silly amount of power down to deflect and hit it on both sides!

 

[magnatom]

But it only happen swhen pushing down on the right crank - so I'd be supprised if this is your issue as you say it happens on both sides. The cage(?) on your front mech is probably wide enough that you'd need to put a silly amount of power down to deflect and hit it on both sides!

Agreed. But I am getting fitter so who knows...

 

[magnatom]

Just to conclude the thread... it turned out to be my back brake being slightly misaligned. Probably something to do with some dodgy road surfaces I went over when doing my Ton! I think putting pressure on the bike warped the wheel just enough to catch the brake. Now sorted.

Thanks