sherpaPeak

how do you figure out if your frame has a crack or not....

okay.......after last weekdends of trail riding my bike needed some cleaning...I finally go the time on wednesday night to take care of it...while I was sashing down the down tube I found a 3 inch hairline mark on the frame/tube. First I thought thought that it may be the mark on the decal...further investigation shows that its not the case......I can feel the hairline separation on in the tube (may be the paint or may be the frame itself).....

now, how could I determine if its a crack or not? I know that I can take it to a local store etc.....I was wondering if there is an obvious way I can determine it before taking it to sewhere else...

thanks for your help

mcoine

a magnifying glass and a good light works well

dminor 

You may be able to 'ping' up and down the downtube (like with a knitting needle, chopstick or whatever you have on hand) and listen. There will be changes in tone from the butting in the tube, but once you get around the area of the suspected crack - - if it is a crack - - there will be a dead 'tick' instead of a 'ping.'

sherpaPeak

I did that......that was my first test.......but as I am not experienced, at least not with cracks......I can hear that there is a thicker ping at the middle of the tube where the suspected crack is...but I can not really be sure. now, if you strike on a tube with a metal the sound created by the either end would be different than the sound created by the middle.......so, the slightly thicker sound that I am hearing..is it the crack or is it just the physics of an hollow tube....

dminor, thanks for your help........that is a wicked bear you have up there.....

dminor 

Only way to know for sure, of course, would be dye penetrant testing (which, if you could find a lab, might cost more than the frame) - -it's like magnafluxing for non-ferrous metals.

Short of that, you may have to scrape away enough paint and clean down to bare metal for a better visual inspection.

The bear - - Friend of mine (actually my old mentor) - - an old-school illustrator and cartoonist - - did that caricature of me and the bear.

DirtPedalerB

if it's right in the middle of the tube I'd keep riding it and watch and see if it expands.. usually the cracks are near the ends at the welds or maybe where the butting begins or ends.. more then likely it's a scratch..
post a pic for all the experts here to overanalize.

wheelhot

another way is to see if you cant stuck something thin (maybe like paper or thinner) into the crack and see if the paper went inside

WannaGetGood

Feel it.