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What an ugly crack


Johan Bornman
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This bike belongs to a friend who lives in the sticks. Last week he sent the bike to me to have a look at the head tube.  I won't reveal what brand it is, but here's a photo of the cracked head tube. The red marks indicate the start and end of the crack.

20100217_005027_Bianchi_Crack.JPG

 

 

The construction of the head tube seems to be a plain tube with two headset cup flanges welded onto each side and then machined to smooth out the weld. The crack started at the bottom of the flange and ends with the out-of-focus bit.

 

On closer inspection I discovered that the headset cup itself is also cracked.

 

20100217_005234_Bianchi_Crack_2.JPG

 

This crack isn't all that clear but look for the dark line in the 25-past position. It corresponds with the crack in the frame.

 

Which crack started first? Which caused what?

 

 

 

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OK, so how much abuse did the bike get to result in a crack like that?

 

Must have been some serias downhill stuff? on a rigid fork?

 
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hmmmmm, that is nasty - goodbye frame & so long

 

Have to almost agree there with DB. Either the cup was too big in diameter & forced in or the cup was really hammered in with more than neccessary force creating the alu to weaken at its already weakest spot

 

just my thoughts
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20100217_010613_20070628crack.jpg?Have I got the wrong topic?

 

 

 

OK, I get it...this guy took a ride on the BIANCHI and then it cracked...!! smiley36.gif smiley36.gif smiley36.gif

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I hope this is not a brand new Bi%$#&i bike??

Oops nearly mentioned the much hidden name of the manufacturer. Perhaps you should have photoshopped it and changed the colour as well - hahahaha!!
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OK' date=' so how much abuse did the bike get to result in a crack like that?

 

Must have been some serias downhill stuff? on a rigid fork?

 
[/quote']

 

It's a road bike!
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The External crack happened first allowing the cup to flex and hence crack, Normally this will happen when the cups are not pressed in straight and it ovalises the frame createing a stress riser...

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You guys crack me up with your humour.

 

Bummer techguy brought sanity to the thread with a well constructed explanation of the crack issue.

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The External crack happened first allowing the cup to flex and hence crack' date=' Normally this will happen when the cups are not pressed in straight and it ovalises the frame createing a stress riser...[/quote']

 

Once a cup is all the way in it is straight.

 

I can't see how ovalisation causes a stress riser. You need a sharp point, not a gentle curve for that.

 

Frame ovalisation at the headset is a different issue not associated with cracks.

 

Think weld...think manufacturing steps.

 

 

 

 
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The External crack happened first allowing the cup to flex and hence crack' date=' Normally this will happen when the cups are not pressed in straight and it ovalises the frame createing a stress riser...[/quote']

 

Once a cup is all the way in it is straight.

 

I can't see how ovalisation causes a stress riser. You need a sharp point, not a gentle curve for that.

 

Frame ovalisation at the headset is a different issue not associated with cracks.

 

Think weld...think manufacturing steps.

 

 

 

 

 

I had a Peugot Tange 2 frame (Steel) many years ago, anyway...the brazing around the head tube lugs started cracking and they replaced the frame with a new one....

 

The new frame had to come from the factory in Europe so in the meanwhile I bought another frame...

 

When i received the new frame from Peugot I no longer needed it and left in a friends bike shop and asked him to sell it for me...

 

Well it hung on display in his shop window for a looong time untill eventualy someone wanted to buy it...

 

When they took the frame down to have a closer look at it they saw it was also cracked around the head tube lugs.

 

Frame had never been used...

 

 

 

 

 
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