cracked cranks (sorry make that snapped)

[DirtParkStreet]

i was giving my bike some much needed attention today and came across this. i have no idea how long they've been cracked for.

http://i27.photobucket.com/albums/c160/freeridefool540/crackedcranks003.jpg
http://i27.photobucket.com/albums/c160/freeridefool540/crackedcranks002.jpg

pretty dangerous eh?, probly pick up a cheapo set of eastern 720? cranks.

updatage, 10 mins ago at my local park havng a boost comp. nearly sliced me leg damn proper

http://i27.photobucket.com/albums/c160/freeridefool540/crackedcranks008.jpg
http://i27.photobucket.com/albums/c160/freeridefool540/crackedcranks004.jpg

[Me+Bike]

Thats odd, they usally dont crack through the weld?

[NH_]

Thats odd, they usally dont crack through the weld?

that would be the one spot i would expect them to crack, welds are the weakest part of it, so it fails first

[Svenn]

same things happened to me a week ago, but mine snapped on a bunnyhop

[PLUCAS]

that would be the one spot i would expect them to crack, welds are the weakest part of it, so it fails first

Strictly not true the weakest part of a welded join is the "HAZ" or heat
affected zone which is directly adjacent to the weld area or right along
the side of the re-enforcement "the ripplily bit"
it is unusual for a weld to fail like this and i would suggest that these
might be no name cranks "a profile copy"

n.b up close it does appear to have failed at the HAZ and then worked throught the weld itself so
Nh would also be correct ??!!

[DirtParkStreet]

Strictly not true the weakest part of a welded join is the "HAZ" or heat
affected zone which is directly adjacent to the weld area or right along
the side of the re-enforcement "the ripplily bit"
it is unusual for a weld to fail like this and i would suggest that these
might be no name cranks "a profile copy"

n.b up close it does appear to have failed at the HAZ and then worked throught the weld itself so
Nh would also be correct ??!!


you definately know your stuff, and yer they are profile copies that came stock on the bike. I can bea real hardass rider when i wanna be so my make takes a flogging most of the time.

plus, the guy i bought it off appaantly dropped of shipping containers to flat on it. duno if its true or not but yer.

[A$h]

I had the same thing happen to my cranks on my norco bmx except the crank was in 2 pieces but my bmx was a piece of junk

[deaks]

that cant be good.

[bowzaa]

I can't believe you could see the crack, then go and keep riding?
nuts

[DirtParkStreet]

I can't believe you could see the crack, then go and keep riding?
nuts

i'd jsut call it stupid..

but yer i did so now i cant ride anywhere and makes me more motivated to hurry up n fix my bike

[Burrito_Boy]

They dk chopstiks?

[tu plang]

Strictly not true the weakest part of a welded join is the "HAZ" or heat
affected zone which is directly adjacent to the weld area or right along
the side of the re-enforcement "the ripplily bit"
it is unusual for a weld to fail like this and i would suggest that these
might be no name cranks "a profile copy"

n.b up close it does appear to have failed at the HAZ and then worked throught the weld itself so
Nh would also be correct ??!!

At the end of the day it's all academic, but the way the crack has grown doesn't really add up with the crack having started at the top in that second pic. Could have opened up further towards the centre of the crack at the inside of the fillet under fatigue. I just can't picture how the crank would be loaded to form a crack at that top point to begin with, its basically on the neutral axis (if you just consider bending load from the rider weight.) What you've said is true for a good weld, though in the case of these cranks, it could have been flawed (the weld that is).

It'd be interesting to see close up.

[francis]

that would be the one spot i would expect them to crack, welds are the weakest part of it, so it fails first

welds arnt the weakest part, there farkin strong its cause the flow of the metal changes in a sudden 90 degree angle and the weld just so hapens to crack, notice how the cracks in the middle of the weld not the outside/edges.

[samc l]

were they by any chance DKs?

[DirtParkStreet]

no they are not DK's.

they are no brand proflile copies that came stock on the bike.

[garrett12]

thats pretty insane... actually ts a little scary