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Poor student, broken frame, can the BB be welded?

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Poor student, broken frame, can the BB be welded?

Old 06-15-13, 03:19 PM
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bp944
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Poor student, broken frame, can the BB be welded?

I put almost all my money into this bike and just finished getting it painted. Turns out the BB of the frame is cracked. I've read a lot of previous posts on this subject and it doesn't look good for me. I know aluminum is very difficult to weld and this is not a good place to have a crack welded. I just can't afford a new frame right now. Its a older felt b2 frame that is really light with a custom paint job. I was going to turn it into a beast of a commuter bike. Is there anyway its salvageable? The crack isn't too long (1.5cm or about 9 threads) but it might keep cracking. What type of welder would have the skills to do something this structural and yet precise? Could I get it TIG welded and then have it re-tapped? I'm pretty desperate here. I live in the Minneapolis area if anyone knows a person or business in particular.







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Old 06-15-13, 03:32 PM
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I do know aluminum is difficult to weld. But, assuming it is safe to repair, I would grind the paint off the area, cut a channel where the crack is, forming a V, then fill it in with weld. Get connected with someone who knows what they are doing when it comes to welding. Talk to a frame builder. Maybe this should go in that forum.
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Old 06-15-13, 03:44 PM
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I could weld it. Worth a try.
I wonder what caused it. Looks like it started at the edge and spread inward.
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Old 06-15-13, 03:45 PM
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Welding on one side of tube will inherently cause it to be out of round, trying to true and re-thread will be challenging at best. A frame replacement and swapping you components would be the least expensive IMHO.
Check with a frame builder as suggested above and GOOD LUCK.
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Old 06-15-13, 03:49 PM
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While looking the pictures again, had a thought about an interference fit sleeve over the offending area.
This may be the least expensive.
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Old 06-15-13, 03:59 PM
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If mine, i would try to fix it for the challenge (free labor for myself). But no idea what someone would charge. Nashbar has frames for $99 sometimes.
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Last edited by Homebrew01; 06-16-13 at 11:30 AM.
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Old 06-16-13, 10:23 AM
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There's a few custom frame builders in the cities and I've been trying to get a hold of them. Its the weekend so I'll probably have to try during the week. I do know that cheap frames can be found but I just dropped $200 in paint alone so I'd rather not toss it just yet.

Prikaus: What is an interface fit sleeve?
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Old 06-16-13, 11:01 AM
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Interference sleeve would be a ring of like metal with an inside diameter slightly smaller than the outside diameter if the bottom bracket,
heat the sleeve to fit over and it will reinforce the area
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Old 06-16-13, 11:03 AM
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By interference fit sleeve, I think he/she is suggesting something like a steel ring that fits tightly around the outside of the BB shell to prevent it from expanding, and thus the crack should not get worse, and it would be usable as-is.
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Old 06-16-13, 11:11 AM
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Originally Posted by bp944 View Post
...I do know that cheap frames can be found but I just dropped $200 in paint alone so I'd rather not toss it just yet...
Frankly, it doesn't matter how much you spent on the paint. At this point, the paint is going to have to be ground down to weld the frame so the paint job is shot. Either way, even the cheapest frame is still more useable than the one you currently have. The suggestion to use a Nashbar frame isn't a terrible idea. At $99.99 regularly, they can be had on pretty much any given holiday sale for 20% off. A good weld would probably run you about that without the assurance that the weld will actually work. My $0.02
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Old 06-16-13, 12:19 PM
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I think I would just drill a small hole at the end of the crack to stop it from propagating and locktite the BB in with a hard set locktite, ride it like I stole it and keep an eye on it. It's probably not worth it to do a proper repair on AL.
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Old 06-16-13, 12:25 PM
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Cotact Frankthewelder over in C&V FTW is a legendary...
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Old 06-16-13, 12:38 PM
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Originally Posted by Homebrew01 View Post
By interference fit sleeve, I think he/she is suggesting something like a steel ring that fits tightly around the outside of the BB shell to prevent it from expanding, and thus the crack should not get worse, and it would be usable as-is.
"HE" says, that is correct sir
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Old 06-16-13, 01:11 PM
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JB weld and a hose clamp





...but honestly, I'd just find another frame and cut your losses.
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Old 06-16-13, 01:30 PM
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Agreed with the Nashbar frame. Sucks, but... that's a very tricky area to fix.
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Old 06-16-13, 01:49 PM
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Don't think a sleeve will work as the weld bead from the chainstay goes to the edge of the BB shell, so you can't really get a ring around there very easily.
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Old 06-16-13, 03:41 PM
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I agree; a new frame is the best option. An interference ring might buy you some time, but it's no guarantee against failure at an inopportune moment. Welding would be tricky, would likely distort the shell and certainly bugger the threads. You'd be looking at the cost of re-tapping and re-facing the shell on top of whatever the welding sets you back. It wouldn't take much to bump up against the price of a new Nashbar frame.
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Old 06-16-13, 05:20 PM
  #18  
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I'm trying to figure out why the OP wasted money on getting a "beast of a commuter bike" painted.

Especially if money is tight.

Bikes are tools not jewels. Function is the only goal.

I guess this is a live and learn moment.

Should have spent the paint money on something else.
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Old 06-16-13, 08:53 PM
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another vote for a nashbar frame.
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Old 06-16-13, 08:56 PM
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Originally Posted by Dean V View Post
Don't think a sleeve will work as the weld bead from the chainstay goes to the edge of the BB shell, so you can't really get a ring around there very easily.
Bit of grinding required, but if money's tight it's worth a shot.

Somebody said a hose clamp and JB Weld and I know it was meant to be a joke, but...honestly, that's not the worst idea I've heard.
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Old 06-16-13, 09:16 PM
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Originally Posted by popeye View Post
I think I would just drill a small hole at the end of the crack to stop it from propagating and locktite the BB in with a hard set locktite, ride it like I stole it and keep an eye on it. It's probably not worth it to do a proper repair on AL.
+1

In addition to what PopEye said, make sure you use a sharp drill bit, Preferably smaller than 1/8". 1/16" would probably be best. Use WD-40 or Tap-Magic AL for a cutting oil. Use a small counter bore to de-burr/chamfer the edge of the hole. Also, take a look at the inside of the BB/DT weld area before doing any drilling to see which tubes/welds are affected by the crack.

Save up for another frame, and don't bother getting it painted this time.

Regarding repair by weld, welding aluminum isn't so difficult. You can use old BB cups to hold the shell in round (and then a big wrench to get them out). Unfortunately, the caveat is that when you do a repair weld to an aluminum frame, you ruin the tempering. Welding usually brings the temper down to T4. Bringing it back up to T6 requires you to heat the frame for several hours at different temperatures, first to reduce the whole frame back to T4 and then back up to T6. I have a friend who's done it (for new frame/tubes, not for repair) with AL 7005. AL 6061 tempering is more time intensive and you need to be more precise. Your Felt is probably 7005, but it'll be hard for you to tell now after removing the decals. Thats also important for matching your filler rod to the base metal.

If you don't temper the frame after welding, you'll likely bend or crack it again. AL loses its temper very quickly because its so conductive. A skilled welder might be able to put some kind of heat sink (AL stock, wet rags, etc) around the work so that the heat affected zone is as small as possible, and you skip the tempering.

Regarding custom paint jobs for commuters... If its supposed to be a sleeper, just stick to the original, hopefully beat-up paint and put a bunch of skateboard/punk/vegan/redneck/indie themed stickers all over it. Then no one will touch it because:

1 its ugly
2 they know you're hardcare because of your sweet stickers
3 they know you're REALLY hardcore because you ride a bike with a cracked bottom bracket. Metal.

Last edited by Sean Gordon; 06-16-13 at 09:25 PM.
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Old 06-16-13, 09:24 PM
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Originally Posted by ahsposo View Post
I'm trying to figure out why the OP wasted money on getting a "beast of a commuter bike" painted.

Especially if money is tight.

Bikes are tools not jewels. Function is the only goal.

I guess this is a live and learn moment.

Should have spent the paint money on something else.
Some people do enjoy having pretty bikes, and that's entirely reasonable.

However, not typically on a commuter, no.
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Old 06-16-13, 09:44 PM
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Aluminum fails catastrophically

I wouldn't trust an aluminum frame that had even one visible crack. Unlike steel frames, aluminum frames often fail catastrophically - all at once rather than slowly break apart. Can you be sure that there aren't any other problems with the frame now that it is covered with a nice coat of new paint? I rode behind a teenager who was riding a pretty fancy aluminum frame MTB on a paved road. He ended up in a heap with the front wheel and half the frame under him and the rest of the bike to the side. He had no warning the frame was about to self destruct. I don't hesitate to ride a 20 year old aluminum MTB but do check it over occasionally.

Last edited by VegasTriker; 06-16-13 at 09:47 PM.
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Old 06-17-13, 12:55 AM
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Clean the area up good and wrap hemp all around the BB area with epoxy resin. Could use fibreglass or carbon unidirectional instead.
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Old 06-17-13, 05:33 AM
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Originally Posted by Dean V View Post
Clean the area up good and wrap hemp all around the BB area with epoxy resin. Could use fibreglass or carbon unidirectional instead.
Or smoke the hemp
A lot of good advise here OP.
Could drill just a small hole at the end of the crack to mitigate further propagation.
Hose clamp + JB Weld is a good one

If you apply JB Weld, make sure you groove the crack for best surface area and adhesion...same principle as welding.

If me, I would look for replacement frame I believe but a hose clamp + JB Weld would likely hold good enough.

With all this stuff, there is some risk, so you have to assess what that risk would be. Having the BB fail or crack greater may not be a catastrophic failure all said. It also depends on your strength and riding style. As a commuter it may last for a while.

Good luck.
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