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#51
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Horst link bending forces
On Tue, 06 Feb 2018 07:32:50 -0800, Joerg wrote:
On 2018-02-05 21:20, dave wrote: On Sun, 04 Feb 2018 09:59:47 -0800, Joerg wrote: snip I've seen injuries with fork failures (TK being a prime example) and with early Al MTB front-end failures. I saw some front-ends detach, although after big impacts that would have ejected the rider in any event. I'm not in the know with MTBs, but it seems that suspension failures would just result in a crippled bike rather than a crippled rider. It depends. If my rear shock detached the bike would bottom out. The posterior mount of that loosened twice, last time on Wednesday, but now I learned the symptoms and carry a 2nd 5mm Allen wrench in a pocket so I can check tightness once in a while without having to unpack the tool kit. Maybe the application of some thread lock may be beneficial. Loctite didn't help. This is on the side of the upper Horst link part that flexes when braking hard. It happens on steep stretches of trail. Though usually only every few hundred miles so a 5mm Allen wrench carried in a quickly accessible pocket is fine. You just have to watch for the symptoms before something down there eats itself. Still. It shouldn't be undoing itself. There are several grades of thread lock available. Maybe up the goop strength or investigate different fasteners. Checking every couple of hundred miles is fine till it comes out 50 after the last check. Good luck with that. -- davethedave |
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#52
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Horst link bending forces
On 2018-02-06 11:21, dave wrote:
On Tue, 06 Feb 2018 07:32:50 -0800, Joerg wrote: On 2018-02-05 21:20, dave wrote: On Sun, 04 Feb 2018 09:59:47 -0800, Joerg wrote: snip I've seen injuries with fork failures (TK being a prime example) and with early Al MTB front-end failures. I saw some front-ends detach, although after big impacts that would have ejected the rider in any event. I'm not in the know with MTBs, but it seems that suspension failures would just result in a crippled bike rather than a crippled rider. It depends. If my rear shock detached the bike would bottom out. The posterior mount of that loosened twice, last time on Wednesday, but now I learned the symptoms and carry a 2nd 5mm Allen wrench in a pocket so I can check tightness once in a while without having to unpack the tool kit. Maybe the application of some thread lock may be beneficial. Loctite didn't help. This is on the side of the upper Horst link part that flexes when braking hard. It happens on steep stretches of trail. Though usually only every few hundred miles so a 5mm Allen wrench carried in a quickly accessible pocket is fine. You just have to watch for the symptoms before something down there eats itself. Still. It shouldn't be undoing itself. There are several grades of thread lock available. Maybe up the goop strength or investigate different fasteners. Checking every couple of hundred miles is fine till it comes out 50 after the last check. Good luck with that. Yes, seems I have to either find better Loctite or have a better set of parts machined for the rear shock pivot. Having to use wrenches a lot happens to other riders as well, the ones that put a lot of miles on their MTBs. Though no complaints since the MTB affords me a lot more fun per mile than the road bike does. Nice scenery, no cars, no Diesel stench, technically interesting rides and I get to meet many animals. -- Regards, Joerg http://www.analogconsultants.com/ |
#53
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Horst link bending forces
Joerg wrote:
On 2018-02-01 11:26, jbeattie wrote: Yes, everything breaks after enough fatigue cycles, particularly aluminum -- which has no fatigue threshold. Even small amplitude fatigue cycles will affect aluminum. It will break. Not necessarily. Next time you fly sit right behind a wing and watch closely what happens at rotation time (when the pilot pulls up and the aircraft becomes airborne). The wing will bend so much that its tip is now several feet higher than it was in its resting state. In turbulent weather it'll then continue to flex up and down like he https://www.youtube.com/watch?v=tr5qkjlE77Y https://www.youtube.com/watch?v=NYsFk4I14N8 Yet these aircraft have a service life of 30 years. And then typically get sold to the freight dogs or lesser devloped countries for another 30 years or so. Do the structural parts of the wing really last that long, or do they get replaced during service? I know nothing about aircraft. It's aluminum. My question is whether the typical upper Host link strut on a MTB can take similar dynamic stresses and for how long. If Boeing made them I'd have no doubt but Boeing does not build MTBs. The aircraft wing flexing is pretty low frequency compared with hammering a bike down a cobblestone road. It does much fewer load cycles per unit time. robert |
#54
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Horst link bending forces
Emanuel Berg wrote:
When everything brakes because of abuse and lack of maintenance, she will not care one bit, except for when it brakes to the point that she cannot use it - then there will be sudden PANIC because how will she now get to the university, shop for clothes, her boyfriend, etc.??? That (and many other) boys will scramble to fix the bike for her. Fact is that the urban young women who ride all those "vintage" bikes these days get sold junk for too much money. Especially the brakes need lots of maintenance to function acceptably, and the frame-mounted friction shifters are so inconvenient to use that the chain often stays in the unsightly left-right (small-small) constellation. Also the old frames tend to be quite large, and compact handlebars didn't exist back then, which makes for an awkward riding position. Since aesthetics is all this is about one SHOULD care about posture and proper chain alignment. robert |
#55
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Horst link bending forces
On 2018-02-06 12:13, Robert Latest wrote:
Joerg wrote: On 2018-02-01 11:26, jbeattie wrote: Yes, everything breaks after enough fatigue cycles, particularly aluminum -- which has no fatigue threshold. Even small amplitude fatigue cycles will affect aluminum. It will break. Not necessarily. Next time you fly sit right behind a wing and watch closely what happens at rotation time (when the pilot pulls up and the aircraft becomes airborne). The wing will bend so much that its tip is now several feet higher than it was in its resting state. In turbulent weather it'll then continue to flex up and down like he https://www.youtube.com/watch?v=tr5qkjlE77Y https://www.youtube.com/watch?v=NYsFk4I14N8 Yet these aircraft have a service life of 30 years. And then typically get sold to the freight dogs or lesser devloped countries for another 30 years or so. Do the structural parts of the wing really last that long, or do they get replaced during service? I know nothing about aircraft. They get repaired when corrosion, cracks or other deficiencies are found and replaced after a structural damage event such as a landing where a wing made ground contact like he https://www.youtube.com/watch?v=trrUkKUyhl4 Otherwise not AFAIK. It's aluminum. My question is whether the typical upper Host link strut on a MTB can take similar dynamic stresses and for how long. If Boeing made them I'd have no doubt but Boeing does not build MTBs. The aircraft wing flexing is pretty low frequency compared with hammering a bike down a cobblestone road. It does much fewer load cycles per unit time. Not really. Look at the 2nd video. That's a lot more flexing per minute than a full-suspension MTB could ever do. On Horst-Link MTB any serious flexing only happens during hard braking and hard upright cornering (where you have a foot on the ground). Cobblestones cause a rattle of the whole bike but not much flexing. In fact, my MTB runs over such roads with the comfort of a Lincoln Towncar or a Citroen DS21. Very different story on the road bike but that's so stiff that not much can flex. What does flex on the road bike is the front end which begins a slight shimmy somewhere above 30mph. So I try to avoid that speed range or hold on tight while going through it on a downhill stretch. At 40mph and above the shimmy stops. -- Regards, Joerg http://www.analogconsultants.com/ |
#56
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Horst link bending forces
On Tue, 06 Feb 2018 07:32:50 -0800, Joerg
wrote: On 2018-02-05 21:20, dave wrote: On Sun, 04 Feb 2018 09:59:47 -0800, Joerg wrote: snip I've seen injuries with fork failures (TK being a prime example) and with early Al MTB front-end failures. I saw some front-ends detach, although after big impacts that would have ejected the rider in any event. I'm not in the know with MTBs, but it seems that suspension failures would just result in a crippled bike rather than a crippled rider. It depends. If my rear shock detached the bike would bottom out. The posterior mount of that loosened twice, last time on Wednesday, but now I learned the symptoms and carry a 2nd 5mm Allen wrench in a pocket so I can check tightness once in a while without having to unpack the tool kit. Maybe the application of some thread lock may be beneficial. Loctite didn't help. This is on the side of the upper Horst link part that flexes when braking hard. It happens on steep stretches of trail. Though usually only every few hundred miles so a 5mm Allen wrench carried in a quickly accessible pocket is fine. You just have to watch for the symptoms before something down there eats itself. When a fastener is used where there is movement in the joint a pinned fastener is usually used. See https://tinyurl.com/ybrca92g -- Cheers, John B. |
#57
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Horst link bending forces
On 6 Feb 2018 20:13:10 GMT, Robert Latest wrote:
Joerg wrote: On 2018-02-01 11:26, jbeattie wrote: Yes, everything breaks after enough fatigue cycles, particularly aluminum -- which has no fatigue threshold. Even small amplitude fatigue cycles will affect aluminum. It will break. Not necessarily. Next time you fly sit right behind a wing and watch closely what happens at rotation time (when the pilot pulls up and the aircraft becomes airborne). The wing will bend so much that its tip is now several feet higher than it was in its resting state. In turbulent weather it'll then continue to flex up and down like he https://www.youtube.com/watch?v=tr5qkjlE77Y https://www.youtube.com/watch?v=NYsFk4I14N8 Yet these aircraft have a service life of 30 years. And then typically get sold to the freight dogs or lesser devloped countries for another 30 years or so. Do the structural parts of the wing really last that long, or do they get replaced during service? I know nothing about aircraft. In Vietnam I worked on a DC-3 (gun ship) that was nearly as old as I was and there was no evidence that there had been any major maintenance or replacement done on the aircraft. It's aluminum. My question is whether the typical upper Host link strut on a MTB can take similar dynamic stresses and for how long. If Boeing made them I'd have no doubt but Boeing does not build MTBs. The aircraft wing flexing is pretty low frequency compared with hammering a bike down a cobblestone road. It does much fewer load cycles per unit time. robert -- Cheers, John B. |
#58
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Horst link bending forces
On 2/1/2018 3:38 PM, Joerg wrote:
Yet these aircraft have a service life of 30 years. And then typically get sold to the freight dogs or lesser devloped countries for another 30 years or so. It's not years, it's cycles, as Aloha 243 demonstrated. https://www.aerotime.aero/upload/content-assets/images/aloha%201.jpg. |
#59
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Horst link bending forces
On 2018-02-07 06:44, sms wrote:
On 2/1/2018 3:38 PM, Joerg wrote: Yet these aircraft have a service life of 30 years. And then typically get sold to the freight dogs or lesser devloped countries for another 30 years or so. It's not years, it's cycles, as Aloha 243 demonstrated. https://www.aerotime.aero/upload/content-assets/images/aloha%201.jpg. Could have been a materials defect but this is what I'd like to avoid and why I posted my question. https://en.wikipedia.org/wiki/Aloha_Airlines_Flight_243 Quote "During an interview, passenger Gayle Yamamoto told investigators that she had noticed a crack in the fuselage upon boarding, but did not notify anyone". Now that I don't understand. Whenever I see something unusual or potentially defective on an aircraft I notify someone from the crew. That has happened more than once. -- Regards, Joerg http://www.analogconsultants.com/ |
#60
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Horst link bending forces
On 2018-02-06 18:24, John B. wrote:
On Tue, 06 Feb 2018 07:32:50 -0800, Joerg wrote: On 2018-02-05 21:20, dave wrote: On Sun, 04 Feb 2018 09:59:47 -0800, Joerg wrote: snip I've seen injuries with fork failures (TK being a prime example) and with early Al MTB front-end failures. I saw some front-ends detach, although after big impacts that would have ejected the rider in any event. I'm not in the know with MTBs, but it seems that suspension failures would just result in a crippled bike rather than a crippled rider. It depends. If my rear shock detached the bike would bottom out. The posterior mount of that loosened twice, last time on Wednesday, but now I learned the symptoms and carry a 2nd 5mm Allen wrench in a pocket so I can check tightness once in a while without having to unpack the tool kit. Maybe the application of some thread lock may be beneficial. Loctite didn't help. This is on the side of the upper Horst link part that flexes when braking hard. It happens on steep stretches of trail. Though usually only every few hundred miles so a 5mm Allen wrench carried in a quickly accessible pocket is fine. You just have to watch for the symptoms before something down there eats itself. When a fastener is used where there is movement in the joint a pinned fastener is usually used. See https://tinyurl.com/ybrca92g That's how I would have done it but designers haven't. At least there should be a locking nut. Some day I might re-do that linkage in a more secure fashion. Not easy, the heads of the screws are sunk into recesses because serious leg injury could otherwise happen. -- Regards, Joerg http://www.analogconsultants.com/ |
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