Johan Bornman Posted February 2, 2009 Posted February 2, 2009 Someone on this thread muses that 1) The 4-bolt design is an over-engineered design.2) That the stem broke because of a twisting action.3) That the stem was "over torqued" ....and then backtracks by saying they should be made "overly strong. Well, the 4-bolt design brings necessary and sensible redunancy. Stems, handlebars and forks that break in use have catastrophic results. The 4-bolt design protects the front-loader stem from failing should one bolt break. If it were a two-bolt design, it would lead to a crash of one bolt breaks. Bolts here are highly stressed and often break. Stems operate in torsion. that's 90 percent of their function. There is no steering torque ona bicycle so they can be very flexible laterally, but have to be extremely rigid in torsion and vertical load. If a stem breaks in torsion and it wasn't abused, it is a poor design and/or made from inappropriate materials. By overtightening the stem you cannot damage the stem's tube. You'll strip the threads or break the bolt off long before the clamp will break. That is evident from examining any stem. Try it, you'll see. A stem, fork and handlebar is a good case in point for strong enough is not always strong enough. And please, lets not gratuitously use fancy words, you don't over-torque something, you over-tighten it.
Guest Big H Posted February 2, 2009 Posted February 2, 2009 That is why I like the BBB stems I use on my Tandems. The torque specification is clearly printed on them.
bustthesickness Posted February 2, 2009 Posted February 2, 2009 Someone on this thread muses that 1) The 4-bolt design is an over-engineered design. 2) That the stem broke because of a twisting action. 3) That the stem was "over torqued" ....and then backtracks by saying they should be made"overly strong.whatever Well' date=' the 4-bolt design brings necessary and sensibleredunancy. Stems, handlebars and forks that break in use have catastrophicresults.wow,I learned something The 4-bolt design protects the front-loader stem fromfailing should one bolt break. If it were a two-bolt design, it wouldlead to a crash of one bolt breaks. Bolts here are highly stressed and oftenbreak.bwahahahahahaaaa Stems operate in torsion. that's 90 percent of theirfunction. There is no steering torque ona bicycle so they can be very flexiblelaterally, but have to be extremely rigid in torsion and vertical load. If astem breaks in torsion and it wasn't abused, it is a poor design and/or madefrom inappropriate materials. YAAAAAAAAAWWWWWN By overtightening the stem you cannot damage the stem'stube. You'll strip the threads or break the bolt off long before the clamp willbreak. That is evident from examining any stem. Try it, you'll see.blah blah blaaaaaaaaahh A stem, fork and handlebar is a good case in point forstrong enough is not always strong enough. blah blah blaaaaaaaaahh And please, lets not gratuitously use fancy words, you don'tover-torque something, you over-tighten it. blah blah blaaaaaaaaahh [/quote'] hahaha, when you're done pumpin' up that ego, please hop back under the stone you came from. cheers
slowpoke Posted February 2, 2009 Posted February 2, 2009 Fanie, i'm relieved to hear your dad is ok - when i saw the topic and started reading i was very worried.
RockCoach Posted February 2, 2009 Posted February 2, 2009 Yeah, I've had an ally handlebar fail next to the stem at 67km/. Catastrophic results indeed. Lesson I learned was that when the bike suddenly starts making creaking sounds from the stem area - you should inspect immediately.
ridesleeprepeat Posted February 2, 2009 Posted February 2, 2009 kcnc part are machined in china, now my limited knowlegde of material quality control leads me to suspect that there could have been a cold joint or a flaw in the original billit the stem was machined from... hard to notice unless ultra sonic or radiographic testing is done before the material is machined... use it don't use it...
Johan Bornman Posted February 3, 2009 Posted February 3, 2009 kcnc part are machined in china' date=' now my limited knowlegde of material quality control leads me to suspect that there could have been a cold joint or a flaw in the original billit the stem was machined from... hard to notice unless ultra sonic or radiographic testing is done before the material is machined... use it don't use it...[/quote'] I'll use it. Only forged critical parts for me, thank you.
Red Zone Posted February 3, 2009 Posted February 3, 2009 kcnc part are machined in china' date=' now my limited knowlegde of material quality control leads me to suspect that there could have been a cold joint or a flaw in the original billit the stem was machined from... hard to notice unless ultra sonic or radiographic testing is done before the material is machined... use it don't use it...[/quote'] I'll use it. Only forged critical parts for me, thank you. Why, I would have thought that a part machined from a single billet of material would have been stronger than a forged part, please explain
daggavis Posted February 3, 2009 Posted February 3, 2009 That is why I like the BBB stems I use on my Tandems. The torque specification is clearly printed on them. JB, does that mean i'm skating on thin ice here with the 2 bolt Easton EA70 stem I have put on my BMC? I don't think EA70 qualifies as weight weenie stuff but is it a proper, strong stem? I looked at the KCNC Fly Ride which was cheaper but somehow I didn't trust it and decided to go with easton... Regards
daggavis Posted February 3, 2009 Posted February 3, 2009 Weird, I wanted to qoute on your 1st post regarding 4 bolt stem designs..somehow pulled in Big H's quote..
Lilo Posted February 3, 2009 Posted February 3, 2009 Sjoe Faan. Eks bly jo pa is oraait!! Stu vi hom groete
ridesleeprepeat Posted February 3, 2009 Posted February 3, 2009 forging is used for a lot of suspension links. forging allows parts to be more resilient by inducing an amount of metal hardening throught the forging process...
Bos Posted February 3, 2009 Posted February 3, 2009 Making sence there Moose, thanks... From What I know forging is a process which forces a "block" of metal into a mould/shape/cavity by sheer force, It can be done while hot or cold (right moose?) what I figure is that the" allignment" of the particles would change as it the shape changes and flow with the new shape of the Item. thereafter the part goes through heat treatment which heats the part to temperatures just below melting and then the part is cooled down again, this "relaxes" the stresses as the particles can re alighn themselves to some extent. CNC, being like a piece of wood that is sculpted to make the stem, seems solid, but the "grain" still makes it strong in one direction more so then other.. My stem is getting a good check this aavy..Sorry for the Hijack Fanie Sterkte vir jou Pa se recovery.
pedal Posted February 3, 2009 Posted February 3, 2009 Fanie, Sorry to hear this sad news about your Dad, hope he is well and not too sore.
RodTi Posted February 3, 2009 Posted February 3, 2009 Geez Fanie - speedy recovery for your dad!! This has grabbed my attention. I ride with that exact same stem - and I'm no lightweight!! What's the consensus now?? Take off the KCNC weightweenie goeters - or trust that that was but one bad piece out of thousands??
Bos Posted February 3, 2009 Posted February 3, 2009 I think we should all Inspect our stuff more regularly.. Mountainbikers keep stuff clean so you can see cracks. One can see stressmarks before cracks and/or faliure if carefully inspected.(I always just grab the bike I admit) Fatugue/stressmarks would show up as what could look like a layer of paint that is comming off, or slight difference in colour around a bolt or down the weld. otherwise slight"wrincles" is also a big warning. but hey, To be sure, How much Is he really saving with that stem? And this does bring the KCNC question up again...I wonder how well they QC their stuff before shipping ? Big companies "should" test stuff from every batch..but who knows If this happens..but It should be more likely than small guys
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