Cracked steel seat tube. What are my options?

andref
andref Posts: 5
edited November 2015 in Workshop
I recently bought an older(1984) steel racer frame with the idea of building up a winter commuter bicycle off an auction site. The seller was slightly less than honest about the condition of the frame and upon bringing it back home I noticed a fairly large crack just below the seat clamp. I should have looked closer while collecting the frame but I was in a hurry so I missed it.

The crack itself does not look super dangerous and I think that with a long seat post it should be safe to use the frame. However painting the frame in its current condition is out of the question since the paint would crack and start peeling off in short order.

2eyj41g.jpg

Options? The way I seee it I have three.

1. Run a weld over the crack. This is perhaps not the best solution since the crack lies near the seat lug.
2. Braze some filler metal into the crack. Would delamination of the filler metal and steel be an issue in this case?
3. Change out the entire seat tube. I want to avoid this as much as I can since this is the most labour intensive option.

Looking forward to what everyone have to say!

Comments

  • ugo.santalucia
    ugo.santalucia Posts: 28,243
    The tube needs to be replaced, which in a lugged frame is possible... chances are the cost will exceed that of buying an other frame on Ebay though
    left the forum March 2023
  • andref
    andref Posts: 5
    ugo: I should mention that the inner surface of the tube is unblemished which means that a piece of metal has delaminated from the outer surface of the tube and that could mean that the crack has not significantly weakened the frame.

    In this case, why would filling in the crack using brazing not be appropriate? As I understand, under the right conditions a brazed crack can be nearly as strong as one that has been welded. Also, Since this crack is high up on the seat tube a longer seat post should not unduly load the cracked zone.
  • Bobbinogs
    Bobbinogs Posts: 4,841
    I think you are trying to convince yourself that patching this is ok and are kind of hoping that enough people will agree.

    I'm afraid I agree with Ugo though, that looks like a write off to me but, if you feel the frame might be really worth it, then it might be worth trying to contact a frame builder to see what a decent swap out would cost...but I would start looking for another frame as the probable plan A...
  • Monty Dog
    Monty Dog Posts: 20,614
    Tube replacement is about £100/tube plus the cost of powder-coat. The crack is in a high-stress area - there's no radius at the bottom of the seatpost slot which has probably led to a stress-concentration crack - brazing probably won't prevent this from carrying-on. Pressed seatcollar lugs shows this isn't a high-end frame - £100 will buy you a half-decent used steel frame that doesn't come with all the aggro.
    Make mine an Italian, with Campagnolo on the side..
  • andref
    andref Posts: 5
    [url=http://www.bikeradar.com/forums/viewtopic.php?p=19729760#p19729760]Bobbinogs[/url] wrote:
    I think you are trying to convince yourself that patching this is ok and are kind of hoping that enough people will agree.

    I'm afraid I agree with Ugo though, that looks like a write off to me but, if you feel the frame might be really worth it, then it might be worth trying to contact a frame builder to see what a decent swap out would cost...but I would start looking for another frame as the probable plan A...

    haha. is that how I sound? :D I'm just new to bicycle repair and I would like to give the frame a fair chance. However it's fairly clear to me now that the frame is not really worth saving and that a new second hand frame is probably the way to go. Thanks for the comment!
  • andref
    andref Posts: 5
    [url=http://www.bikeradar.com/forums/viewtopic.php?p=19729770#p19729770]Monty Dog[/url] wrote:
    Tube replacement is about £100/tube plus the cost of powder-coat. The crack is in a high-stress area - there's no radius at the bottom of the seatpost slot which has probably led to a stress-concentration crack - brazing probably won't prevent this from carrying-on. Pressed seatcollar lugs shows this isn't a high-end frame - £100 will buy you a half-decent used steel frame that doesn't come with all the aggro.

    That sounds spot on. The frame is from an old Swedish bike and probably cost £300-400 new. Might make a nice wallhanger though. Thanks for the comment!
  • me-109
    me-109 Posts: 1,915
    If it's meant to be a cheap winter hack, what have you got to lose? Keep it cheap. Get a fab shop or mate to blast it and run a quick weld over it. The lug will still flex because you won't be filling the expansion slot. Deburr the inside yourself with files, Dremels, etc and give a 'cheap' spray over with some cans. Use, abuse and check every so often.
  • rolf_f
    rolf_f Posts: 16,015
    [url=http://www.bikeradar.com/forums/viewtopic.php?p=19730329#p19730329]Me-109[/url] wrote:
    If it's meant to be a cheap winter hack, what have you got to lose? Keep it cheap. Get a fab shop or mate to blast it and run a quick weld over it. The lug will still flex because you won't be filling the expansion slot. Deburr the inside yourself with files, Dremels, etc and give a 'cheap' spray over with some cans. Use, abuse and check every so often.

    Or maybe a metal collar around the top of the seat tube below the lug? If this was a Parisien commuter hack then you'd get some funny looks if you suggested scrapping the frame based on that!
    Faster than a tent.......
  • crankycrank
    crankycrank Posts: 1,830
    Hard to tell for sure from the photo but it looks like a crack is starting where the right seat stay is joined at the seat clamp lug. :shock:
  • me-109
    me-109 Posts: 1,915
    [url=http://www.bikeradar.com/forums/viewtopic.php?p=19730481#p19730481]crankycrank[/url] wrote:
    Hard to tell for sure from the photo but it looks like a crack is starting where the right seat stay is joined at the seat clamp lug. :shock:
    Good spot! Looks like a second crack at that joint.
  • keezx
    keezx Posts: 1,322
    Frame can be ridden safely with a seatpost of sufficient length and collar clamp around the cracked area.
    Any serious money will be a waste.
  • mattsccm
    mattsccm Posts: 409
    Get your seatpin set right then dog a jubilee clip around it nice and tight. Maybe 2.

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