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Oil, rim valve hole, rubber disintegration
Ti ~12 year old Specialized Ground Control
Oil source: leaky shock fork. Oil has been dripping out from under the shock boot and down the left fork leg for the past several years (~4 to 5 years?). Oil reached the hub and flowed along the spokes to the rims. Most of the oil flow probably happened over a short period of time and the flow probably decreased or stopped after enough oil was lost. Before I cleaned up the fork and wheel this past week, a thick layer of dirt and oil covered the fork leg and front hub, with a lesser layer on the hub-facing side of the rim. (Yes, I haven't cleaned this bike in years, but I just overhauled the hubs yesterday...)The rim sidewalls were relatively clean being swept by the brake pads. The plastic rim strip covered the spoke holes well, but the valve hole was open to the oil covered hub-facing side of the rim. The first two photos are from one side of the tire, the next two are from the other side. The black patch is where the damage is. The yellow gum rubber (?) is absent from those patches, and when back lit, you can see light between the nylon threads of the casing. (Sorry, no back lit photos, my camera's LCD is broken and I can't adjust the settings very well.) The oil probably got to this part of the tire by flowing down the presta valve of the tube to the interior of the tire. The rest of the tire is pretty dirty and has evidence of oil on the outer "skinwall" part, but it is more of a diffuse damage. http://img200.imageshack.us/img200/7500/img25659fq.jpg http://img200.imageshack.us/img200/5199/img25660ky.jpg http://img200.imageshack.us/img200/5817/img25685hx.jpg http://img200.imageshack.us/img200/9366/img25698mt.jpg How did I happen to notice this damage? Well, the tube just suddenly went flat on me yesterday and when I inspected the tube, I found the leak at the valve base. Then I remembered the Carl/Jobst/Mark discussion on this topic a few weeks ago. The tube is a Performance branded tube with one patch on it. It has been on the bike for years - I don't remember my last flat on this bike, and I haven't lived near a Performance shop in over 6 years. It is possible that this is a defective tube, but it has already survived many years. I haven't had to use a frame pump on this bike in many years, so it wasn't bad pumping technique (I've never damaged a tube using a frame pump anyway). I really can't say if the tube was defective or if oil weakened the tube. Maybe it was a combination of those factors. Here is the tube: http://img200.imageshack.us/img200/3103/img25705yb.jpg |
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Oil, rim valve hole, rubber disintegration
On Tue, 19 Jul 2005 21:15:59 -0800, "Andrew Lee"
whatsupandrewathotmaildotcom wrote: Ti ~12 year old Specialized Ground Control Oil source: leaky shock fork. Oil has been dripping out from under the shock boot and down the left fork leg for the past several years (~4 to 5 years?). Oil reached the hub and flowed along the spokes to the rims. Most of the oil flow probably happened over a short period of time and the flow probably decreased or stopped after enough oil was lost. Before I cleaned up the fork and wheel this past week, a thick layer of dirt and oil covered the fork leg and front hub, with a lesser layer on the hub-facing side of the rim. (Yes, I haven't cleaned this bike in years, but I just overhauled the hubs yesterday...)The rim sidewalls were relatively clean being swept by the brake pads. The plastic rim strip covered the spoke holes well, but the valve hole was open to the oil covered hub-facing side of the rim. The first two photos are from one side of the tire, the next two are from the other side. The black patch is where the damage is. The yellow gum rubber (?) is absent from those patches, and when back lit, you can see light between the nylon threads of the casing. (Sorry, no back lit photos, my camera's LCD is broken and I can't adjust the settings very well.) The oil probably got to this part of the tire by flowing down the presta valve of the tube to the interior of the tire. The rest of the tire is pretty dirty and has evidence of oil on the outer "skinwall" part, but it is more of a diffuse damage. http://img200.imageshack.us/img200/7500/img25659fq.jpg http://img200.imageshack.us/img200/5199/img25660ky.jpg http://img200.imageshack.us/img200/5817/img25685hx.jpg http://img200.imageshack.us/img200/9366/img25698mt.jpg How did I happen to notice this damage? Well, the tube just suddenly went flat on me yesterday and when I inspected the tube, I found the leak at the valve base. Then I remembered the Carl/Jobst/Mark discussion on this topic a few weeks ago. The tube is a Performance branded tube with one patch on it. It has been on the bike for years - I don't remember my last flat on this bike, and I haven't lived near a Performance shop in over 6 years. It is possible that this is a defective tube, but it has already survived many years. I haven't had to use a frame pump on this bike in many years, so it wasn't bad pumping technique (I've never damaged a tube using a frame pump anyway). I really can't say if the tube was defective or if oil weakened the tube. Maybe it was a combination of those factors. Here is the tube: http://img200.imageshack.us/img200/3103/img25705yb.jpg Dear Andrew, If oil had gotten onto the inner tube, I'd expect it to feel softer and to look shiny and darker than the surrounding dry rubber--the rubber soaks up oil and loses tensile strength. Cut two chunks of inner tube, dunk one in oil for a few days, and you'll see what I mean--the oil-soaked tube feels and looks quite different. I don't see any traces of oil on your tube, nor any sign of oil on the valve stem itself--in fact, there's rust where it meets the tube: http://img200.imageshack.us/img200/3103/img25705yb.jpg If the leak is right at the base, I'd wonder a little about the effect of the rust on a 6-year-old tube. The damage to the tire sidewall is another matter, but again there doesn't seem to be any corresponding oily patch of inner tube. I'd be pleased to see signs of oil damaging an inner tube (well, sorry for you, but pleased in a ghoulish way), but to me your tube looks dry and untouched by oil. The light shining through the oily patch on the tire is interesting, probably something along the lines of the Homer Simpson diet test as prescribed by Dr. Nick: "And remember, if you're not sure about something, rub it against a piece of paper. If the paper turns clear, it's your window to weight gain." http://www.httpcity.com/ronq/simp/comedy.html It looks as if the oil dripped directly from shock to sidewall and spread out, rather than hitting the rim, oozing through the valve hole, and spreading onto the tire. Again, there's no apparent oil path from the rim to the nicely rounded dark smear on the inside of the tire sideway. Because it's unlikely that the valve-hole area just happened to be right under the leaky shock all the time, I wonder if the pictures actually show a non-oil related problem. The dark smears on the inside might be where the thickened rubber bulge of valve-area acted like a motorcycle-rim security-bolt. That is, the smears may show where the stiffened rubber patch around the valve-stem was causing a little trouble. Carl Fogel |
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Oil, rim valve hole, rubber disintegration
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Oil, rim valve hole, rubber disintegration
"Andrew Lee" whatsupandrewathotmaildotcom wrote:
wrote: If oil had gotten onto the inner tube, I'd expect it to feel softer and to look shiny and darker than the surrounding dry rubber--the rubber soaks up oil and loses tensile strength. Cut two chunks of inner tube, dunk one in oil for a few days, and you'll see what I mean--the oil-soaked tube feels and looks quite different. I wonder what kind of physical (visual) evidence a single drop of oil getting on that section of the tube would leave. Would it be as obvious as a tube soaked in oil for days? I really don't know - I suppose there's a test called for there somewhere... ;-) Unfortunately the only real-world test would require dripping a drop of oil or two on my own bike's stem, and seeing if I have to stop to change a flat due to a stem base failure. :-( Maybe I'll do that after it cools off - it's no fun changing a tube when the temperature is in triple digits! Mark Hickey Habanero Cycles http://www.habcycles.com Home of the $695 ti frame Good point. I wasn't thinking about how an oiled tube would be different. There is an irregular shaped bump in the rubber surrounding the valve that got me thinking that something might have happened to the rubber, but looking at another (good) tube now, I see something similar. But the good tube has much better support around the base of the valve. I think this might be one of those defective tubes that Jobst talked about. It has just been handled gingerly enough that it lasted so long. I'd be pleased to see signs of oil damaging an inner tube (well, sorry for you, but pleased in a ghoulish way), but to me your tube looks dry and untouched by oil. Yes, darn for you. I wish that I could say that I was able to tear the tube up into bits with my bare fingers at the valve... Because it's unlikely that the valve-hole area just happened to be right under the leaky shock all the time, I wonder if the pictures actually show a non-oil related problem. The dark smears on the inside might be where the thickened rubber bulge of valve-area acted like a motorcycle-rim security-bolt. That is, the smears may show where the stiffened rubber patch around the valve-stem was causing a little trouble. Good call, I think. The patches are shaped like the stiffened rubber patch of the the tube. So, maybe this says something about the difficulty of actually getting oil on a tube and weakening it enough to cause problems? There was quite a bit of oily residue on this rim, more than I imagine would be left on a rim from oiling nipple seats. |
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