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Scratch or fracture?

Posted: 14 Aug 2011, 12:52pm
by humpy
I've had my bike about 10 weeks now, and a few days ago noticed a knocking kind of noise. When I was out on it today, I noticed whenever I put a little bit of pressure on the pedals it appeared, light pressure or no pedalling meant no noise. When I got back I looked at the bike, and noticed either a scratch on the paint or fracture in the aluminum frame on the chain stay. If I run my nail over it, I can feel it. I would have thought it'd be an akward place for a scratch to be, and I can't remember ever scratching this. I'll probably have to take it the LBS. Pics below (and yes my bike needs a clean!). If it's a fracture, is this a common place for it to occur?

rsz_photo0187-a.jpg

Photo0187-b.jpg

Re: Scratch or fracture?

Posted: 14 Aug 2011, 1:46pm
by TonyR
Press down hard on the chainstay. Does the "scratch" move?

Re: Scratch or fracture?

Posted: 14 Aug 2011, 4:35pm
by mattraisin
As you have no mudguards that is a place stones and other debris will rattle arround so scratch isn't unusual there but its the length that is confusing, could your foot of slipped out and scratched it with the cleats? I would say it doesn't look like a fracture as any stress in that area would go at the weld first and aluminium isnt known for long smooth cracks. That sort of noise can be the most deceptive, start with the least exspenisve/more easy fixes and go from there. It could be seat rails/clamp, seat post, loose or overtightened spokes, loose cranks, damaged BB, damaged hubs, cracked rims, loose chain rings, worn rear cassette etc. I suggest the spokes are a good place to start, along with the seat clamp and seat.

Re: Scratch or fracture?

Posted: 14 Aug 2011, 5:21pm
by ferrit worrier
I see from the picture you've got a shimano chainset and possibly "Tiagra" try nipping up the play in the cranks, slacken off the two socket head bolts and turn the plastic? plug on the outside of the none drive crank, that should take out the clunk, it did with mine :D That looks like a scratch to me, one way to test, clean the area with a good detergent. then dust with talcum powder if there is a crack any oil or such like will be drawn out by the talc and you will get a dark line. or try polishing out the line with "T" cut. IMO It's too clean a line to be a crack, you would expect the paint to have a rough edge.

Re: Scratch or fracture?

Posted: 14 Aug 2011, 5:50pm
by Gearoidmuar
Looks like a scratch. Look at it with a powerful magnifying glass, or a hand lens as fuddy duddies call it.

Re: Scratch or fracture?

Posted: 14 Aug 2011, 6:26pm
by humpy
TonyR wrote:Press down hard on the chainstay. Does the "scratch" move?
It doesn't appear to.
mattraisin wrote:As you have no mudguards that is a place stones and other debris will rattle arround so scratch isn't unusual there but its the length that is confusing, could your foot of slipped out and scratched it with the cleats?
My feet only come of the cleat on the outside and I can't see how it could be caused by that. The cleat would be near the pedal which is away from where the scratch is. I would probably remember too if I accidentally hit my frame. If it is a scratch, perhaps a stone or something else.
mattraisin wrote:That sort of noise can be the most deceptive, start with the least exspenisve/more easy fixes and go from there. It could be seat rails/clamp, seat post, loose or overtightened spokes, loose cranks, damaged BB, damaged hubs, cracked rims, loose chain rings, worn rear cassette etc. I suggest the spokes are a good place to start, along with the seat clamp and seat.

Thanks, I'll check that out.
ferrit worrier wrote:try nipping up the play in the cranks, slacken off the two socket head bolts and turn the plastic? plug on the outside of the none drive crank, that should take out the clunk, it did with mine :D That looks like a scratch to me, one way to test, clean the area with a good detergent. then dust with talcum powder if there is a crack any oil or such like will be drawn out by the talc and you will get a dark line. or try polishing out the line with "T" cut. IMO It's too clean a line to be a crack, you would expect the paint to have a rough edge.

Thanks, I'll have a go at this in the next few days.
Gearoidmuar wrote:Look at it with a powerful magnifying glass

Good idea, will check it out.

Thanks all for your comments :D

Re: Scratch or fracture?

Posted: 14 Aug 2011, 6:49pm
by Si
if the bike is only a few weeks old i'd be inclined to return it to the shop and let them decide what the problem is. If they say that it's only a scratch ask them to put it in writing!

If you are still unsure then the safest thing to do is sand the paint off and see what the metal is like underneath.

Re: Scratch or fracture?

Posted: 14 Aug 2011, 8:27pm
by wirral_cyclist
That isn't the edge of a chainstay protection sticker is it?

Re: Scratch or fracture?

Posted: 14 Aug 2011, 9:21pm
by Valbrona
Looks like scratch to me. I do not think a crack that length would very likely form along the length of the chainstay like that.