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Attempt at aluminum head tube crack repair.

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Attempt at aluminum head tube crack repair.

Old 05-17-16, 08:01 PM
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Originally Posted by Andrew R Stewart
Well when you decide a path that 100+ years of industrial experience hasn't found to be the best solution what do you expect? Andy
I wasn't around 100 years ago so i wouldn't know.
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Old 05-17-16, 08:13 PM
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It isn't about being a "naysayer". You have asked for opinions on your repair (which I commend you for the effort), and the majority of them, including mine, are that it won't hold. I don't know how many 'pros' are contributing, but if the opinion of it being unsafe keeps coming up, as it does, i would take heed and not just wave them away as naysayers.
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Old 05-17-16, 08:20 PM
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Originally Posted by kennj123
I wasn't around 100 years ago so i wouldn't know.
But you can stand on the shoulders of those who were with good research methods. The world did record history before the interweb was invented by Gore. Andy (who is trying to be kind but firm)
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Old 05-17-16, 08:24 PM
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Originally Posted by d4vide
It isn't about being a "naysayer". You have asked for opinions on your repair (which I commend you for the effort), and the majority of them, including mine, are that it won't hold. I don't know how many 'pros' are contributing, but if the opinion of it being unsafe keeps coming up, as it does, i would take heed and not just wave them away as naysayers.
naysayers say just based on their say so. their seems to be little real info or experience in this field. I guess its up to me to blaze a new trail.
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Old 05-17-16, 08:27 PM
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Indeed... or see a welder
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Old 05-17-16, 08:55 PM
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Originally Posted by kennj123
naysayers say just based on their say so. their seems to be little real info or experience in this field. I guess its up to me to blaze a new trail.
Well, combined together, the responses to your question probably represent a couple centuries of experience with bikes, so there's that.

You could, if you were of an engineering bent, calculate the tensile strength of aluminum alloy at the thickness of the head tube, then compare to the tensile strength of epoxy and mat. (The steel wire is doing nothing, because you've wound it in a spiral.)

But the most practical thing is to simply ride the bike until it either breaks or doesn't. You don't seem to mind the way it looks.

Last edited by jyl; 05-17-16 at 08:58 PM.
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Old 05-17-16, 08:58 PM
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Let's try to separate the wheat from the chafe a bit.

First of all, understand the likely cause, which is corrosion, most likely rusting of the steel cups, which expanded the rube beyond it's limit. It is not related to any stresses, so likely will be self limiting even if you do nothing, though you do want to knock out the cups, and stop the corrosion process (I'd use a zinc based paint).

Secondly it's not likely to be dangerous, because even id the tube splits over it's entire length, where are the fork and headset going to go.

I have similar cracks on my two bikes in Cozumel, the result of a crappy painted steel headset, and the island's high humidity and salt air. I've elected to do nothing, and if and when the tube is split enough that I get headset float (not yet so far), I'll decide whether a repair is warranted.

As for what the OP is doing, the tube has to be under some ring tension to keep the headset tight. So, before reinforcing it, the head cup should be removed, and the tube pulled closed. That way there'll be tension when the cup is pressed back in.

IMO, the best repair would be a steel ring fitted to both ends. Next, would be steel wire wound with as much tension as possible in the type of tight array used to secure fittings to fishing poles. Third, and easiest, though probably shortest lived, would be to remove the cups, clean everything as well as possible, then bond the cups in with high strength adhesive.

Some of the methods can be combined, like wound wire + bonded cups, but there are no assurances, and it's all only a question of slowing a terminal process.
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Old 05-17-16, 09:15 PM
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Originally Posted by jyl
(The steel wire is doing nothing, because you've wound it in a spiral.)
Spiral hurts nothing. wire is set in mat and the epoxy and mat between wire and tube has excellent compression property so load is transfered to wire. wire has excellent tensile property so it won't allow epoxy + mat to split like the head tube did. I've done quite a few fixes with epoxy around my house and on my boat. Its almost as versatile as duct tape. (duct tape saved my life one time so I'm partial to it).

Last edited by kennj123; 05-17-16 at 10:08 PM.
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Old 05-17-16, 10:07 PM
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Originally Posted by FBinNY
Let's try to separate the wheat from the chafe a bit.

First of all, understand the likely cause, which is corrosion, most likely rusting of the steel cups, which expanded the rube beyond it's limit. It is not related to any stresses, so likely will be self limiting even if you do nothing, though you do want to knock out the cups, and stop the corrosion process (I'd use a zinc based paint).

Secondly it's not likely to be dangerous, because even id the tube splits over it's entire length, where are the fork and headset going to go.

I have similar cracks on my two bikes in Cozumel, the result of a crappy painted steel headset, and the island's high humidity and salt air. I've elected to do nothing, and if and when the tube is split enough that I get headset float (not yet so far), I'll decide whether a repair is warranted.

As for what the OP is doing, the tube has to be under some ring tension to keep the headset tight. So, before reinforcing it, the head cup should be removed, and the tube pulled closed. That way there'll be tension when the cup is pressed back in.

IMO, the best repair would be a steel ring fitted to both ends. Next, would be steel wire wound with as much tension as possible in the type of tight array used to secure fittings to fishing poles. Third, and easiest, though probably shortest lived, would be to remove the cups, clean everything as well as possible, then bond the cups in with high strength adhesive.

Some of the methods can be combined, like wound wire + bonded cups, but there are no assurances, and it's all only a question of slowing a terminal process.
I just didn't want to spend much money on it or time. I only paid 125$ for the bike then another 30$ on new tires. LBS said doing anything on their end would be too expensive compared to bike value and likely hood of them fixing anything. Thats why I decided on a hail mary before i tossed the bike and bought something else. Personally I give the repair 80+ probablity of success over next 2 years of moderate usage. I have 2 other bikes I use quite a bit as well.
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Old 05-17-16, 10:22 PM
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If you did not drill a smalls top hole at the end of the crack it will keep growing even under your bodge Job.

Dont think its fixed . keep shopping for a replacement Bike ..
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Old 05-17-16, 10:36 PM
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Its not the right way to make a repair. All you did was cover up the problem. Sadly your defenses have no real basis in repair or mechanical stability.

You did what you wanted to do, so get on the bike and ride. If you encounter the same thing again, please pass on that purchase and continue looking for a bike that doesnt have safety defects.

-SP
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Old 05-17-16, 10:46 PM
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Normally, the frame would be trashed. The epoxy isn't going to work. If I was intent on keeping the frame, I would've given AlumiWeld a try. Check it out on YouTube.

Aluminum repair kits, repair aluminum by welding with a Propane Torch - Alumiweld

Clean the paint coating off the head tube, v the crack with a Die Grinder or Dremel Tool and drill the end of the crack. Then apply the AlumiWeld with a propane torch. Use a file and abrasive paper to clean up the surface and then refinish the head tube.

I think it would be a better fix than epoxy. And, you should be able to keep an eye on it to see if it cracks again. Otherwise, look for a replacement frame on eBay or locate a frame builder that could replace the head tube.

Frame Repairs - Head tubes | GripSport

https://www.bikeframerepair.com/


That epoxy fix is foolish.

Last edited by tgolden; 05-17-16 at 11:13 PM.
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Old 05-17-16, 10:52 PM
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Originally Posted by kennj123
Lots of naysayers here. I did an experiment on a piece electrical conduit and tried to bend it and the strength was excellent.
The problem is that a headtube takes a LOT of POUNDING. That's upward forces being applied to that headtube from the fork. The lower headset cup is most likely an overly tight fit in some way and that's what caused the crack to start in the first place.

Drilling small holes at the end of a crack is STANDARD OPERATING PROCEEDURE to insure that the crak doesn't get bigger. That small round hole is called a STRESS RELIEVER and you don't have them. Also, your repair has done NOTHING to strengthen the INSIDE of that head tube.

To put it another way. You haven't REPAIRED THE PROBLEM YOU'VE SIMPLY COVERED IT UP! The way it is now it could fail without warning or giving visual clues that the crack is getting better.

This is NOT naysaying, it's advice given with experience.

Cheers
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Old 05-17-16, 11:01 PM
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Weld the crack and put a collar on the headtube.



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Old 05-17-16, 11:38 PM
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Originally Posted by kennj123

And what is all the concern about how the bike looks anyway. Do you guys pickup a lot of chicks with your really nice bikes?

...all the damn time. It's almost embarrassing at this point.
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Old 05-17-16, 11:42 PM
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Originally Posted by tgolden
Normally, the frame would be trashed. The epoxy isn't going to work. If I was intent on keeping the frame, I would've given AlumiWeld a try. Check it out on YouTube.

Aluminum repair kits, repair aluminum by welding with a Propane Torch - Alumiweld

Clean the paint coating off the head tube, v the crack with a Die Grinder or Dremel Tool and drill the end of the crack. Then apply the AlumiWeld with a propane torch. Use a file and abrasive paper to clean up the surface and then refinish the head tube.

I think it would be a better fix than epoxy. And, you should be able to keep an eye on it to see if it cracks again. Otherwise, look for a replacement frame on eBay or locate a frame builder that could replace the head tube.
Exactly what I did with an old aluminum frame made of Columbus Altec 2 with a 1" crack coming from the bottom of my headtube. Also drilled a hole at the end of the crack before grinding a V the length of the crack. I was ready to trash the frame but had some of these alu propane rods on hand. Piled on a little extra material for strength and decided to use the bike for short errands while waiting for it to start cracking again. 1k miles later it's still holding and has taken some good hits from potholes and my 200lb arse. I wrapped a wet cotton towel around the headtube, top and downtubes to keep from melting the rest of the frame. Fortunately the headset cups fit perfectly after the repair so no distortion occurred. Be very careful not to get the alu too hot or you will liquefy your frame. Of course your results may vary but I had very good results with this.
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Old 05-17-16, 11:51 PM
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.
...heat treating welded aluminum alloy bicycle frames
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Old 05-18-16, 12:11 AM
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Technically, AlumiWeld isn't welding; it's brazing. The difference between welding and brazing is that welding melts the base metal where brazing doesn't. I'm not sure if brazing would require heat treating on series 6000 aluminum alloys; probably not, because you're only heating the base metal to 730° F.
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Old 05-18-16, 12:25 AM
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Originally Posted by kennj123
Spiral hurts nothing. wire is set in mat and the epoxy and mat between wire and tube has excellent compression property so load is transfered to wire. wire has excellent tensile property so it won't allow epoxy + mat to split like the head tube did. I've done quite a few fixes with epoxy around my house and on my boat. Its almost as versatile as duct tape. (duct tape saved my life one time so I'm partial to it).
If the goal is to stop the head tube from actually splitting i.e. expanding a lot (like to stop the crack from opening wide), then the wire and epoxy might work. But the crack only expands the tube by a very tiny amount - the tube's circumference at the crack is maybe 0.2 mm larger than it originally was.

Consider the impact force on a headset when a 150-200 lb rider and 20-30 lb bike hit a pothole or similar at speed. It's a lot - sometimes enough to brinnel, i.e. dent, a hardened steel bearing race, which is far, far stronger than a thin steel wire and a little epoxy.

Versus that force, a couple spiral wraps of wire over some fiberglass mat and some epoxy isn't going to be resistant enough to prevent 0.2 mm of expansion, and thus the crack lengthening. I realize it is steel wire, but steel is elastic. Attach a couple hundred pound weight to that wire and drop it from some height, the wire will stretch even if it doesn't break. Just 0.2 mm of stretch will be enough for the crack to lengthen.

Maybe you'll baby the bike enough, or ride it seldom enough, that this won't be an issue. Maybe the crack was only due to corrosion, and not to applied force. So maybe the crack won't get worse, or maybe it will. But the wrap won't make a difference either way.

Last edited by jyl; 05-18-16 at 12:31 AM.
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Old 05-18-16, 12:52 AM
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Originally Posted by jyl
Attach a couple hundred pound weight to that wire and drop it from some height, the wire will stretch even if it doesn't break. Just 0.2 mm of stretch will be enough for the crack to lengthen.
that experiment is not applicable. The wire is a twisted strand with lots of surface area and well anchored in the epoxy. The tiny amount of the wire just over where the crack is propagating would have to stretch the .2mm or tear. More likely the bond between the aluminum and epoxy isn't good enough and the aluminum tube implodes from the stress. I did an experiment with a piece of electrical conduit and thats how it failed. But the surface was much harder and I didn't make it nearly as rough as I was able to make the aluminum.

As for the hole to stop the crack propagation:
https://www.quora.com/Is-it-possible...ke-it-stronger
Tan Zheng Jie mentioned drilling holes to prevent crack propagation. Although it is done on shop floors, it is just a quick fix and reduces overall load bearing capability (as he has pointed out). Welding would be a better option and it actually adds material to the structure.

Also, I was worried I would have to take the fork off and drill into an empty head tube to be able to drill deep enough to make the hole round, or risk damaging what was in the head tube. I just didn't feel like wasting the time. I felt the surface prep of the aluminum was so good the epoxy would spread the stress over a very large area and dissipate it.


As f
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Old 05-18-16, 01:22 AM
  #46  
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Epoxy resin tensile strength is about 4,000-8,000 psi, depending on source. What's the cross section of the epoxy layer that is securing the wire over the crack area, maybe 0.05 sq inch?

How much force was required to produce the crack? Aluminum alloy tensile strength is about 40,000 psi.

I am not sure how you did the experiment with conduit. Sounds like you wrapped some steel conduit in wire and epoxy and bent it to failure. Suppose you had taken that piece, placed a hardened steel expander cone in the open end, and hit it dozens of blows with a couple hundred lb hammer. Then see whether the end expanded even 0.2 mm. That's more similar to headset/headtube forces.

Last edited by jyl; 05-18-16 at 01:28 AM.
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Old 05-18-16, 02:00 AM
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The epoxy fix is a fool's errand. Consider the loads the head tube is subjected to and the material specs for epoxy, and compare that to AlumiWeld, brazing, or welding.

No matter what method of repair you consider, the end of the crack needs to be drilled to have any hope of arresting the propagation.
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Old 05-18-16, 02:46 AM
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Originally Posted by jyl
Epoxy resin tensile strength is about 4,000-8,000 psi, depending on source. What's the cross section of the epoxy layer that is securing the wire over the crack area, maybe 0.05 sq inch?

How much force was required to produce the crack? Aluminum alloy tensile strength is about 40,000 psi.
Hence the reason i put the stranded wire on there two. steel has 3x the tensile property of aluminum.
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Old 05-18-16, 02:55 AM
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Originally Posted by tgolden
The epoxy fix is a fool's errand. Consider the loads the head tube is subjected to and the material specs for epoxy, and compare that to AlumiWeld, brazing, or welding.

No matter what method of repair you consider, the end of the crack needs to be drilled to have any hope of arresting the propagation.

it comes down to how well the epoxy adheres to the aluminum. I was very happy with the rough surface i created and I'm very optimistic. The epoxy/mat/wire will spread the stress over a large area so the hole is irrelevant.
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Old 05-18-16, 03:33 AM
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Originally Posted by kennj123
it comes down to how well the epoxy adheres to the aluminum. I was very happy with the rough surface i created and I'm very optimistic. The epoxy/mat/wire will spread the stress over a large area so the hole is irrelevant.
You couldn't be more wrong. It's obvious you don't have any background in engineering, metal working, or machine maintenance. It's not a matter of how well the epoxy adheres to the aluminum. The crack will continue to propagate. And, now that you've concealed the failure from view, you've set yourself up for a sudden catastrophic head tube failure.

In addition to the fix I indicated previously, I would then measure the outside diameter of the head tube bottom and top with a good micrometer and have a machine shop fabricate a collar of series 7000 aluminum as indicated in cobba's post and have it pressed on and then brazed as well.

If you think your fix is adequate, you should show the engineering analysis.

Last edited by tgolden; 05-18-16 at 03:16 PM.
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