#21
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Seized quill stem
On 12 Feb, 19:08, Jobst Brandt wrote:
Instead of offering rhetorical questions, As rethorical as you might have read it, it perhaps deserved a better answer. how about a positive suggestion on how to fix it? That's exactly what I wrote in another, this time quite positive, message. Should I divulgate a picture of a frame that I scorched to free a similarly stuck component? Tell you what. A heat shock also freed a stuck cartridge bottom bracket after two local competent bike mechanics had not been able to remove it. They had given up the effort, feeling the risk of twisting the frame (with the extractor held firm in the vise). Heat waves can do wonders. Sergio Pisa |
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#22
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Seized quill stem
Jobst Brandt wrote:
Heat has no effect on aluminum oxide inside a steel steertube. sergio wrote: You serious, Jobst? Isn't this statement a tad too bold? Well, narrowly, he's right. The aluminum oxide isn't affected at these temperatures but the aluminum stem core does expand, shrink or melt effectively. Jobst notes that the aluminum oxide layer is inert but I don't think that phenomenon has any practical effect in the instant case of a stuck stem. One removes the oxide layer in shards easily with a pick after the stem is out. -- Andrew Muzi www.yellowjersey.org/ Open every day since 1 April, 1971 |
#23
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Seized quill stem
On 12 Feb, 19:46, AMuzi wrote:
Jobst notes that the aluminum oxide layer is inert but I don't think that phenomenon has any practical effect in the instant case of a stuck stem. Pardon me. The shrinkage or expansion, upon cooling or heating below melting point, of any (very thin) layer is minimal compared to the dimensional change of the (relatively massive) components nearby. Was that the message? Why should one negate the fact that the adhesion through the oxide layer gets compromised by the heat shock? Isn't this some relevant effect? Sergio Pisa |
#24
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Seized quill stem
On 12 Feb, 19:54, Jobst Brandt wrote:
Heat waves can do wonders. From my experience that is wishful thinking, rather than fact. I am not sure how solidly your seized parts were attached. Not so according to my experience. For example, I was able to unscrew easily a rather stuck pedal by heating with the flame of a candle. This other time I had to free a seatpost. After struggling with brute force, I tried with the heat: no success. Then I took the thing over to a retired framebuilder, Gino Vanni, an old man who happens to be a friend of mine. I asked him to melt the aluminum out. Before resorting to the flame, ailing Gino grabbed the saddle that was still in place and freed the post. Lesson n.1 for me After heating up I should have waited until cool, better yet if I had cooled it with a 'negative' shock. Sergio Pisa |
#25
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JB FAILED again Seized quill stem
On 12 Feb, 18:08, Jobst Brandt wrote:
Sergio Servadio wrote: Heat has no effect on aluminum oxide inside a steel steertube. You serious, Jobst? Isn't this statement a tad too bold? Instead of offering rhetorical questions, how about a positive suggestion on how to fix it? *I went through the quill stem failure with several Cinelli stems and a steel Ritchey stem Any intelligent rider would have got either some paint or oil in there after the third time. Plugging the bottom of the steerer mitigates the condensation which causes the corrosion (mixed in with salts, possilbly from sweating). before the threadless steertube came along, for which I was glad and have used ever since with no problems and amazingly greater handlebar stiffness. The quill stem rocks around from side-to-side above its expander in the steertube (pumping in fluids) where, in contrast, the threadless stem is ultimately stiff. *A great feeling. Jobst Brandt |
#26
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Seized quill stem
On 12 Feb, 19:14, sergio wrote:
On 12 Feb, 19:54, Jobst Brandt wrote: Heat waves can do wonders. From my experience that is wishful thinking, rather than fact. *I am not sure how solidly your seized parts were attached. Not so according to my experience. For example, I was able to unscrew easily a rather stuck pedal by heating with the flame of a candle. This other time I had to free a seatpost. After struggling with brute force, I tried with the heat: no success. Then I took the thing over to a retired framebuilder, Gino Vanni, an old man who happens to be a friend of mine. I asked him to melt the aluminum out. Before resorting to the flame, ailing Gino grabbed the saddle that was still in place and freed the post. Lesson n.1 for me After heating up I should have waited until cool, better yet if I had cooled it with a 'negative' shock. Sergio Pisa Come to think of it, when releasing the screws on an aging car door, I whacked 'em not only hot, but as they cooled down before they released. They not only released tyhe bond, but were positively free, not anywhere representative of the torque applied (without effect before the heat and cool cycle). |
#27
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Seized quill stem
On 02/12/2010 06:02 PM, Jobst Brandt wrote:
Frank Leake wrote: snip In the true path of RBT, "This ones really stuck, I may need a bigger blowtorch..." Heat has no effect on aluminum oxide inside a steel steertube. As I said, saw the stem off at the top of the steertube and bore it out. You have earned the course in threadless steertubes. Do it. I'm no engineering type, but I would have thought the expansion wotsit between the steel outer and aluminum inner would have been a, to coin a phrase, **** of a lot. The stuck steerer tubes and seat tubes I've had usually give way to a bit of heat. |
#28
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Seized quill stem
On 2010-02-12, Jobst Brandt wrote:
Sergio Servadio wrote: Instead of offering rhetorical questions, how about a positive suggestion on how to fix it? As rhetorical as you might have read it, it perhaps deserved a better answer. That's exactly what I wrote in another, this time quite positive, message. I didn't see how heating aluminum would make it shrink away from the steel steertube or how heat would loosen aluminum oxide that had chemically expanded between the stem and steertube. I think the idea is just that things move a bit relative to each other and that breaks the bond gluing them together, even if you're actually making the part that's on the inside bigger. |
#29
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Seized quill stem
In article
, sergio wrote: On 12 Feb, 18:02, Jobst Brandt wrote: Heat has no effect on aluminum oxide inside a steel steertube. You serious, Jobst? Isn't this statement a tad too bold? Al2O3. Melting point: 2072 deg C. Mostly insoluble. The Al sits at the bottom of a deep electrochemical trench. Fe melting point: 1535 deg C. -- Michael Press |
#30
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JB FAILED again Seized quill stem
Jobst Brandt wrote:
Trevor M. Jeffrey wrote: Heat has no effect on aluminum oxide inside a steel steertube. You serious, Jobst? Isn't this statement a tad too bold? Instead of offering rhetorical questions, how about a positive suggestion on how to fix it? Â I went through the quill stem failure with several Cinelli stems and a steel Ritchey stem before the threadless steertube came along, for which I was glad and have used ever since with no problems and amazingly greater handlebar stiffness. Any intelligent rider would have got either some paint or oil in there after the third time. Plugging the bottom of the steerer mitigates the condensation which causes the corrosion (mixed in with salts, possilbly from sweating). The failure occurs from rider sweat and rain water that has adequate access at the upper end of the aluminum stem, even though lock rings on head bearings were equipped with an O-ring so small that it pumps when the stem swivels from side to side. It does not come in from the bottom, although various frame makers offered plugged forks without any effect believing it came from below. These were a nice gestures, recognizing the effect, but not its cause or solution. The quill stem rocks around from side-to-side above its expander in the steertube (pumping in fluids) where, in contrast, the threadless stem is ultimately stiff. Â A great feeling. The wooden plugs of old were supposed to keep a crown/column crack from killing the rider. In my experience they hold moisture inside the column anyway. -- Andrew Muzi www.yellowjersey.org/ Open every day since 1 April, 1971 |
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