# Fixing a seat tube crack in an Al frame



## mmorra (Dec 28, 2004)

I have an Al Javelin Amarone frame built I believe in 2005. There is a small crack starting at the slot in the seat tube just below the seat post clamp area. I have attached an image. The frame requires a 32.4 mm post, so my plan was to use a seat post shim to convert it to a 27.2, thus giving me some extra support and metal in the cracked area. Hopefully this will prevent the crack from getting bigger. I am also thinking about using JB Weld to cement the shim in the frame. I know that this will be permanent, but I thought I could better prevent additional cracking if the shim and tube were fused together with JB Weld. Anyone have other ideas? I don't know how well welding the crack would work. The Al is pretty thin. My experience with Al frames indicates that this problem will probably get worse if I don't do something. I bought this frame used, so I don't know its history or anything about how the crack got started. All advice appreciated.


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## cxwrench (Nov 9, 2004)

i would bet that jb welding the shim in will probably work pretty well...and you've really got nothing to lose, right? probably last for years


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## ziscwg (Apr 19, 2010)

My neighbor does welding and one time I asked him about welding a cracked Al bike frame. He laughed and said, "Unless you're an expert and know exactly what type of Al you are working with, it's a lost cause. You'll do more damage than repair."

So, IMHO, your shim idea sounds possible. Although, I'm not sure if welding or brazing the shim in place is the best idea. Maybe a strong epoxy?


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## danl1 (Jul 23, 2005)

ziscwg said:


> My neighbor does welding and one time I asked him about welding a cracked Al bike frame. He laughed and said, "Unless you're and expert and know exactly what type of Al you are working with, it's a lost cause. You'll do more damage than repair."
> 
> So, IMHO, your shim idea sounds possible. Although, I'm not sure if welding or brazing the shim in place is the best idea. Maybe a strong epoxy?


JB Weld is an epoxy. 

Plan sounds reasonable, but I'd recommend _not _using epoxy around the whole of the shim, but only away from the clamping slot. You'd want the two materials to be able to move relative to one another for clamping effectiveness. That's also another interface to corrode which you won't be able to protect with grease, so as a solution it's probably somewhat short-lived. If it's not going to see too much weather, it may last a few years.


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## ziscwg (Apr 19, 2010)

danl1 said:


> JB Weld is an epoxy.
> 
> Plan sounds reasonable, but I'd recommend _not _using epoxy around the whole of the shim, but only away from the clamping slot. You'd want the two materials to be able to move relative to one another for clamping effectiveness. That's also another interface to corrode which you won't be able to protect with grease, so as a solution it's probably somewhat short-lived. If it's not going to see too much weather, it may last a few years.


Sorry, Im not familiar with JB weld. When OP said "cement to the frame" I thought he meant it figuratively, not literally.

It would be nice to know how this works out.


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## DaveG (Feb 4, 2004)

How much did you pay for this frame? I can't help noticing that several cracks are forming. Maybe your idea would work for a while. I'd check the frame very carefully all over before I'd ride it. If it was inexpensive, I would just toss it


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## Touch0Gray (May 29, 2003)

you know..I would carefully scrape away the paint to see how the metal REALLY looks underneath


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## mmorra (Dec 28, 2004)

*JB Weld*



ziscwg said:


> Sorry, Im not familiar with JB weld. When OP said "cement to the frame" I thought he meant it figuratively, not literally.
> 
> It would be nice to know how this works out.



I have used JB Weld on a loose headset in a Bridgetstone MB1 mountain bike steel frame and it has held for several years. Don't ever plan to get them out though, because they are really stuck. It beats tossing the frame in the scrap heap.


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## mmorra (Dec 28, 2004)

*price and cracks*



DaveG said:


> How much did you pay for this frame? I can't help noticing that several cracks are forming. Maybe your idea would work for a while. I'd check the frame very carefully all over before I'd ride it. If it was inexpensive, I would just toss it


The other cracks appear to be just the paint. The one noted actually shows on the inside of the seat tube. I paid $200 for the frame on ebay.


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## Kerry Irons (Feb 25, 2002)

*Toast*



DaveG said:


> How much did you pay for this frame? I can't help noticing that several cracks are forming. Maybe your idea would work for a while. I'd check the frame very carefully all over before I'd ride it. If it was inexpensive, I would just toss it


I agree. Stick a fork in it - it's done. The OP can ride it if he wants, JB Weld or not, but I would be inspecting that thing after every ride and have a spare frame in the basement ready to do a parts swap.


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## laffeaux (Dec 12, 2001)

I had a similar crack, but in a steel frame. I had it repaired by a frame builder, and it's held up fine. He welded on an insert to cover the crack and reinforce it. Aluminum is a bit tricker, as it may require heat treating afterward, but if you really want to keep the frame consider a professional repair.

Here's what the repair looked like:

<img src="https://www.eandsweb.com/bikes/pics/mtbr/DSC01827.JPG">


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## gr8blues (Nov 20, 2009)

You know I have jb welded everything you can think of and it is magic stuff, Give it a try just like you said, what have you got to loose? Alu frames are pretty cheap so if it looks even a little bit sketchy after you ride it, trash it and buy another one. When bonding clean and sanded is the secret.


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## Touch0Gray (May 29, 2003)

surgically clean......the sanding will give you a bit of mechanical bond as well as a polar bond on the molecular level. I would do the final clean with acetone before gluing. You got nothing to lose by trying except your time and the materials...I like repairing stuff that is not repairable...that is pretty much how I make my living!


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## Cbookman (Jul 2, 2009)

Drill a small hole at the very end of the crack first to stop it from growing larger. 

I wouldn't use JB weld. In fact, I hate that sh1t. It's a garbage epoxy that people think works wonders. 

Follow T0G's advice - use something like 80-120 grit to give the epoxy more surface area for bonding, and do the same with the seat post shim. 


Any autobody repair supplier has a bunch of epoxy systems that will make the seatpost shim a permanent replacement. Just make sure you put a slot in the shim to enable some clamping force to be applied before you set the shim in place. While at the autobody place grabbing the epoxy, grab some wax and grease remover too for the cleaning part. 


And remember - longer cure times = stronger bond.


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## Mr. Versatile (Nov 24, 2005)

mmorra said:


> The other cracks appear to be just the paint. The one noted actually shows on the inside of the seat tube. I paid $200 for the frame on ebay.


I'm not so sure about that. Nobody ever wants to hear this, but if were my frame I'd start looking for another one right away.


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## been200mph (May 28, 2004)

Devcon or Z-Spar Splash Zone would be the two possible epoxy choices I'd use before JB Weld; as the previous poster alluded to being not that good.


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## blakcloud (Apr 13, 2006)

An alternative would be to have the frame professionally repaired. Though I don't know his work I have gone to his website and he does repair aluminum frames.

http://www.eagleoneresearch.com/BicycleRepair.htm 

This is just another option open to you.


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## mmorra (Dec 28, 2004)

*Fixed*

Here are some images of what I did to the frame. So far so good, but it hasn't seen a lot of use yet. What I noticed about the epoxy is that it is very hard and brittle upon drying, so it is not a filler. JB Weld is much more flexible and seems to be a better filler than glue. I picked the slowest drying metal epoxy I could find.

I roughed up all the surfaces with emory cloth and drilled a hole at the end of the crack. I didn't see any other cracks on the inside of the seat tube. I used a commercially available shim. The one issue I had to watch was epoxy accumulation at the bottom of the shim when I inserted it. The shim accumulated epoxy at the leading edge and I had to make sure and clean it off, or it would block the seatpost and not allow it to extend below the bottom of the shim. 

Time will tell if this holds. Thanks for all the advice. Matt


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