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Dents in the top tube

Old 04-14-19, 06:54 PM
  #26  
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Can a dent in an aluminum tube be rolled out?
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Old 04-14-19, 07:05 PM
  #27  
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I rode a Trek 6500 Alpha ZX as a daily, year-round commuter for about 8 years. It had a serious (big and deep) dent in the top tube that never affected anything. I remember being nervous about it for several months, than never thought about it again.
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Old 04-21-19, 11:29 AM
  #28  
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As mentioned, earlier, I am not a fan of a dented frame set, however; the seller dropped the price on my newest Cyclops from $1500.00 CND to $600.00 CND, when the dents were noticed. The dents (very small) do bother me but the bike is my Canadian rider and aesthetics come second on my riders...
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Old 04-21-19, 11:45 AM
  #29  
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Bikes with a dent or two are the fast ones.
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Old 04-21-19, 02:35 PM
  #30  
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It needs a bullet hole for real street cred.
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Old 04-21-19, 06:22 PM
  #31  
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Originally Posted by T-Mar View Post
The reliability of a dent is a function of the size of the dent, particularly the width and sharpness of any crease. Sharp creases significantly increase the probability of failure. It won't asplode but it may buckle under loads that normally wouldn't affect it. Of course, the thinner the tubing, the more susceptible it is. Frame blocks are a popular shop tool for removing dents because they reduce the size of the dents and crease, reducing the probability of failure, though at the expense of the paint finish.

As an extreme but easily demonstrable example of how a dent impacts the structural strength of a tube, get an undamaged aluminum soda pop can. Try to buckle it by pushing inwards on the ends. Or try bending it. It's not easy to do. However, if you use your thumb to put a small dent with a crease into the side of the can, the loads required to buckle the can drop significantly. Dents have the same effect on a bicycle tube. However, it's very hard to predict the new, reduced load limit. Moderate dents may be fine for everyday use but could cause the tube to buckle under a bigger impact, such as hitting a curb or pothole. It's impossible to predict.
The stress in the middle of a bicycle frame tube (where dents occur) is minimal. I've yet to see a frame buckle due to a dent. You're more likely to have a frame break from something you can't see, such as incomplete brazing at a lug or bottom bracket.
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Last edited by gugie; 04-29-19 at 11:40 AM.
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Old 04-22-19, 06:33 AM
  #32  
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You may not have seen such failures but I have. While there is less stress in the non-butted, middle sections of the tube, dents lower the stress that the frame can tolerate without buckling. While it's impossible to predict the new load limit and when/if the frame will fail, it will fail at lower load than one with virgin condition tubes.

BTW, in my experience, the most common frame builder related failures are due to overheated joints.

Last edited by T-Mar; 04-22-19 at 06:38 AM.
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Old 04-29-19, 11:03 AM
  #33  
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For the record, I stripped the seafoam green bike I asked about on April 7th. Felt rather uneasy about it, and not like I don't own other good bikes.
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Old 04-29-19, 11:19 AM
  #34  
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Originally Posted by Slightspeed View Post
It needs a bullet hole for real street cred.
What was that, a .22? The HPx would have taken it, no problem.
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Old 04-29-19, 11:30 AM
  #35  
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Originally Posted by Gary Fountain View Post
I know you're not asking how to fix the dents but small dents can be repaired with bodyfiller and a file to bring it back to round but the best way to fill the hole is to remove the paint from the area and bronze fill the dent but this takes some nerve and skill so a hole isn't blown into the tube with the 'Oxy' torch. Either way, the tube will need re-painting.

I wouldn't use bronze to fill a dent. The temperatures you need to get to are significantly higher than silver-based filler, the tube is pretty thin right there to start with, and I'd be worried about putting a hole in it. I've had 100% success rounding the tube out using aluminum frame blocks and grease as best possible, cleaning and filling the remaining small dent with 50% silver with a tiny flame, and just melting the filler so it stays proud of the dent. Fine file and sand it smooth.



frame blocks and grease, roll it back and forth to remove most of the dent



Silver filled dents
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Old 04-29-19, 11:44 AM
  #36  
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Originally Posted by T-Mar View Post
You may not have seen such failures but I have. While there is less stress in the non-butted, middle sections of the tube, dents lower the stress that the frame can tolerate without buckling. While it's impossible to predict the new load limit and when/if the frame will fail, it will fail at lower load than one with virgin condition tubes.

BTW, in my experience, the most common frame builder related failures are due to overheated joints.
Pix or it didn't happen?

I've seen some crappy production frames where there's a signficant braze "miss". The relatively thick lugs used on a lot of them possibly make up for that. Thin tubing and lugs are more likely to have the "cooked tubes" syndrome.
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Old 05-01-19, 08:09 AM
  #37  
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Originally Posted by gugie View Post
Pix or it didn't happen?
I figured the probability of your response invoking the "no pics" rebuttal would be about 99.7%.
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