Telling cracks from scratches

Since starting cycling just under a year ago I have read a lot about aluminium frames and cracking
and so when I clean my bike I regularly check for cracks.

Perhaps I'm getting a bit paranoid about it, considering the huge number of ally bikes being sold
(some very expensive) it must be a sound material for frames. Anyway, I've seen a couple of pictures
on web sites showing cracks in ally frames which show as dark hairline. My problem is that after a
few thousand miles on gritty country roads with plenty of loose stone about my bike has plenty of
scratches and grazes on the frame which, once a bit of dirt of oil gets in them start to look like
these images of cracks. It's not helped by a large proportion of my frame being white.

Some of these marks disappear once a bit of frame cleaner or GT85 has been used on them whilst
others steadfastly refuse to shift. So, my question is, how do you tell whether something is a crack
in the frame or just a scratch on the paint/varnish? Non of them appear to be widening or
lengthening over time. Also, just how prone are aluminium frames to cracking (mine is a plain guage
7005 T6 one) am I getting a bit too concerned about the possibility?

Thanks for any thoughts, Paul.

 

On Sun, 8 Jun 2003 21:31:26 +0100, "Paul" <[email protected]> wrote:

>So, my question is, how do you tell whether something is a crack in the frame or just a scratch on
>the paint/varnish?

Go to an industrial engineering shop and buy a crack detecting dye kit. It's pretty easy to use, not
expensive to buy, and the most complex tooling you're likely to need is a hairdryer and a UV
blacklight (mine cost $5 from a security marking kit)

 

On Mon, 09 Jun 2003 11:09:40 +0100, Andy Dingley <[email protected]> wrote:

>On Sun, 8 Jun 2003 21:31:26 +0100, "Paul" <[email protected]> wrote:
>
>>So, my question is, how do you tell whether something is a crack in the frame or just a scratch on
>>the paint/varnish?
>
>Go to an industrial engineering shop and buy a crack detecting dye kit. It's pretty easy to use,
>not expensive to buy, and the most complex tooling you're likely to need is a hairdryer and a UV
>blacklight (mine cost $5 from a security marking kit)

A few days ago Jobst posted a link to the company that makes Zyglo (A product which I have used with
great success)... they are now selling a product called spotcheck which looks from their web site
like an excellent option for the above sort of situation.

They also have a dealer locator on their page...

http://www.magnaflux.com/index.asp