Cracked stem
03-28-17 | 04:27 PM
#28
Thread Starter
Senior Member
Joined: Feb 2004
Posts: 2,159
Likes: 5
Correct. Just took off the Thomson and it indeed did crack all the way through the metal at the 3:00 position. It weighed in at 138 grams and the Easton EA 90 I replaced it with weighed 128 grams.
03-28-17 | 06:03 PM
#29
Senior Member
Joined: Dec 2009
Posts: 28,682
Likes: 63
From: Houston, TX
Bikes: 1990 Romic Reynolds 531 custom build, Merlin Works CR Ti custom build, super light Workswell 066 custom build
The FSA OS-99 all alloy stem is a good one. Lighter and cheaper and so far I have no complaints.
04-29-17 | 06:52 PM
#30
Bicyclist, ex racer
Joined: Mar 2009
Posts: 38
Likes: 0
From: San Diego
Bikes: 2 Equipes , Turbo. 91 Miyata Team 1000, 710, 610, 210, 110, canti mixte . Santana very early
Good observation strange place to start failing. I know this sounds stupid but are you sure it's a crack. Sometimes you can chase a crack to see how deep and get some clues. Do you use TRI bar extensions or did you have a loose headset? One things for sure, this stem is not up to par. A stem should be able to take regular loads a few times over before a yield. I lost a little respect for this company.
04-29-17 | 06:55 PM
#31
Bicyclist, ex racer
Joined: Mar 2009
Posts: 38
Likes: 0
From: San Diego
Bikes: 2 Equipes , Turbo. 91 Miyata Team 1000, 710, 610, 210, 110, canti mixte . Santana very early
Thanks for the information on ball burnishing.
Please do not read this as some kind of critique or warning, but.....
Thomson, like many makers of "machined from billet" stems don't do a step that was common BITD of forged quill stems.
Ball burnishing "tightens" up the surface structure of aluminum parts, partly duplicating and/or enhancing the effects of near net forging. By compressing and flowing the surface it closes surface micro cracks that may otherwise become the seeds from which cracks grow.
As mentioned, ball burnishing used to be SOP, but has gone out of fashion, probably for cosmetic reasons. Also keep in mind, that aluminum, (both forged and machined) is vulnerable to corrosion, which cause surface defects that later start the cracking/fatigue process.
On the bright side well designed and built can tolerate crack formation for quite a while before failing. I suspect that this stem's crack woulf have become obvious either by sight or sound (creaking) or even by feeling looser well before it let go.
So, don't obsess, but don't neglect or take your aluminum parts for granted either.
Thomson, like many makers of "machined from billet" stems don't do a step that was common BITD of forged quill stems.
Ball burnishing "tightens" up the surface structure of aluminum parts, partly duplicating and/or enhancing the effects of near net forging. By compressing and flowing the surface it closes surface micro cracks that may otherwise become the seeds from which cracks grow.
As mentioned, ball burnishing used to be SOP, but has gone out of fashion, probably for cosmetic reasons. Also keep in mind, that aluminum, (both forged and machined) is vulnerable to corrosion, which cause surface defects that later start the cracking/fatigue process.
On the bright side well designed and built can tolerate crack formation for quite a while before failing. I suspect that this stem's crack woulf have become obvious either by sight or sound (creaking) or even by feeling looser well before it let go.
So, don't obsess, but don't neglect or take your aluminum parts for granted either.
