Skyhawk GT2-A Frame Fail

Discussion in 'General Questions' started by Timbone, May 23, 2015.

  1. Timbone

    Timbone Active Member

    After Thursday's commute home on the motorbike, something didn't feel right just as I got off the bike. I did a simple flex test and, yes, the Skyhawk Aluminum frame was flexing. Flexing too much at that..

    It took a few minutes but I finally found a crack that traveled half way around the downtube, just below the bottom weld of the in frame gas tank.

    Here are my options as I see them:

    Could simply buy a new frame: $120-150.

    Could buy a new bicycle and move all the stuff over. I have more than enough parts! $40-150.

    Could try to find a welder to weld a new aluminum support piece. $20-60.

    I am working on finding a decent tig welder because my other option has failed. I had a plan:

    I have some propane so I went to Harbor Freight and picked up some of those alumalloy rods as I have used them in the past with good results. My idea was to braze the rod into the crack, grind it down and then braze an aluminum collar around the area to bulk it up.

    This was a fail. The aluminum rod melted but rolled right off the base metal. Attempts to braze the aluminum collar over the crack failed, too. The rod adhered nicely to the aluminum collar, but it would not braze the piece to the bike frame. I thought it was going to but it just wouldn't. I hda scrubbed and cleaned the entire area very well. I figure there must be some kind of alloy in the aluminum bike frame.

    Anyway, a good welder could fix this up in a hurry.

  2. troyg

    troyg Member

    AL and MAB's don't mix, for long. Even welded it's too dangerous, if possible go steel.
  3. butre

    butre Well-Known Member

    the problem with the gt2a frames is that there's no bracing to keep that aluminum piece from shaking around, so they tend to break right where you described. you need to have gussets welded to the pedestal or you need to buy one of bikebobber's miami mod mounts, but unfortunately bikebobber isn't doing business anymore. I believe you can still get clones of his design from mzmiami on ebay
  4. butre

    butre Well-Known Member

    Timbone likes this.
  5. Large Filipino

    Large Filipino New Member

    The GT2A already has the pedestal mount. I really would like to see a pic of this crack if you can Timbone.
  6. butre

    butre Well-Known Member

    the pedestal is the problem, it's unsupported and causes frame cracks. you need to gusset it or use miami mod mounts
  7. Large Filipino

    Large Filipino New Member

    Oh okay. I get it now.
    Following this because I bought the same frame.
  8. butre

    butre Well-Known Member

    I've got the same frame too, gonna switch to something else when it cracks. for now it looks cool as hell though
  9. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

    That is not where he said this frame failed.

    Aluminum framed Felts never crack.

    There is no comparison between these Chinese frames and a Felt.

    The aluminum feels thin and they probably don't heat treat the welds

    There are other quality made aluminum frames too.
  10. Timbone

    Timbone Active Member

    Good reading! Actually, I created my own bomb proof motor mounts out of steel and worked around the pedestal mount. That thing is designed to fail.

    The more serious problem I am confronting is a crack failure far up the downtube, just below the bottom weld on the gas tank. Looks like the crack started out of the weld on the inside and has worked a little over half way around. This frame is unrideable now.

    I'll put up a pic of this tomorrow. I cleaned the damaged area carefully but the alumalloy rod would not take to it. There must be some kind of annealing in the aluminum that prevented brazing.

    I am convinced that a decent TIG welder could fix this up and give this frame another year's life. Gotta find him, though! I can TIG weld, but I don't have the equipment.
  11. Timbone

    Timbone Active Member

    Here's the picture of the frame crack:


    It's in one of the worst places possible.

    I talked to a TIG welder. he told me he could probably rig a temporary repair but, being that the aluminum is seriously compromised, he figured new cracks would start appearing.
    Large Filipino likes this.
  12. KCvale

    KCvale Motorized Bicycle Vendor

    There are also knock-off GT2A frames, gasbike has been selling them for over 2 years.

    The real Grubee Skyhawk frame can't be found there, Don won't sell to them and took them off the official China Gas registered Skyhawk distributer list for stealing his designs and getting cheap knock-off's made but still using his known brand name on them.

    I don't know if the real deal is any better than a knock-off or not, but they had to save money somewhere to undercut the price.

    Just on a side note, there is a new fat tire disc brake equipped GT2A frame coming this year that will take 26" x 3" wheels ;-}
  13. Timbone

    Timbone Active Member

    You guys never asked what I did. I have effected a repair that is holding.

    I tried to braze alumalloy into the damaged area / crack. Complete fail.

    I am not gonna waste a penny to have a TIG welder TRY to fix this.

    I went to Lowe's and bought some Fiber Fix. This is a resin soaked material that clings intensely to metals costing about $7. I followed the directions and wrapped the hell out of the downtube on and around the damaged area. The frame is rigid again, and I've successfully ridden my moto about 30 miles. This stuff is tough!

    Of course, I am extremely conscious of the damage and I am inspecting this area before, during and after every ride.

    I think I have saved myself plenty of time to find a new frame for my next, best build yet. It has to be perfect. I am going to be picky!
  14. butre

    butre Well-Known Member

    that's pretty good, I never thought of just fiberglassing the crack. that might be a good cheap solution for the pedestal mount too
  15. The_Aleman

    The_Aleman Active Member

    My first build was on a Schwinn Alloy Seven, which was a 6061 T6 aluminum version of the classic 1955 cantilever Schwinn design.

    My frame cracked in the very same place, and I found it the same way OP did. Bike felt loose all of a sudden, so I stopped and had a look.

    Sadness. I ended up moving everything, wheels included, to a new frame. A steel frame.

    It is my belief that aluminum frames are generally unsuitable for MaBing in the long term, especially with a chinagirl. Aluminum frames fatigue much quicker than steel.

    One thing's for sure: I never liked any of Grubee's bike frames. They remind me of older Hyundais and Kias: they look okay, but upon further study are rather shoddy.
  16. KCvale

    KCvale Motorized Bicycle Vendor

    Nice solution.

    I'd bet that Caswell epoxy sealant would do the same thing maybe even without a fiberglass mesh for strength, that Caswell just flat amazed me with it's tenacity to permanently bond to anything and after a couple of days of curing be incredibly strong all on it's own.
  17. The_Aleman

    The_Aleman Active Member

    Good luck with that.
  18. Timbone

    Timbone Active Member

    I know that Trek, among other bicycle manufacturers, had sold numerous models using composite frames of aluminum and carbon. Probably still making them.

    This got me to thinking: TIG welding requires real skill and expensive equipment. Mig welding on steel tubes is super tricky.

    With resin joints, you could really build anything in terms of a frame very inexpensively. I am accumulating a lot of parts and materials. Just picked up a pristine old Schwinn frame off a curb. Time for experiments!