My frame broke.

Discussion in 'Motorized Bicycle General Discussion' started by a_dam, Jun 9, 2009.

  1. a_dam

    a_dam New Member

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    Did that get your attention? Not as scary as it sounds - no close encounter of the road kind. On my last ride, I noticed a slight rattling or buzzing noise. I had just got into town about seven miles from home. I did a pretty good roadside check of motor mounts, engine components, anything that could be rattling loose. Couldn't find a problem, and I was hoping that my motor wasn't making a death rattle. When it was time to go home, I ran the motor as usual. Same noise - no better - no worse.

    Back home a with a thorough scrutiny I spotted a sneaky little crack all the way through the rear brake mount between the seat stays. I was glad that my motor wasn't causing the noise, but a cracked frame isn't really GREAT news. The stress and vibration of the 2-cycle might have hastened the metal failure. But the motor mounts that I made by brazing pieces of iron plumbing pipe together are doing fine after a couple thousand miles. The frame is a 1973 Continental and it looked pretty beat up when I got it, so maybe there was a weak spot to begin with.

    In the pic below the motor and brake caliper is removed and I've stripped down to bare metal for the welding. My neighbor welded it for me and it looks sturdy now. Since it's all apart, I'm making a better motor mount and will have to repaint the back end. I'll try to take some pics of the interesting parts as I go.
     

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    #1 a_dam, Jun 9, 2009
    Last edited: Jun 9, 2009
  2. reg454

    reg454 New Member

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    well good that it wasent too bad and that you have a guy that can weld it to you. underneath my myspace link is a post to a thread that I made with some mods. Look down to the clutch arm remake it's a good mod and you can make it in about an hour or 30min if you have a piece of billit alum 1/2" thick.
     
  3. 2door

    2door Moderator
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    A-Dam,
    Glad it wasn't more serious and you're on your way back to the road. That's an odd place for the frame to crack. There really doesn't appear to be that much motor induced stress at that point. Like you said, it might have been a weak area originally and just decided it couldn't take the vibes. Good luck. Keep us posted on the repair.
    Tom
     
  4. reg454

    reg454 New Member

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    Thats where your brakes go right, could have been all the stress from stopping from all the dirt trails weeeeeeeeeeeeee.
     
  5. a_dam

    a_dam New Member

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    Wow, has it been 9 days already?

    I've been getting around on leg-power lately, and it really wasn't a bad as I thought it would be. Most of the days had light wind. Yesterday sucked, though. I rode west about 8 miles and the wind was strong from the northwest. Good for coming back home, right? NO. In less than 3 hours it switched on me. Had to fight it again going back. I was so mad. A car was passing me and some young idiot was standing up out of the sunroof and I think he yelled "wanna race?", just as I was yelling "M*F*". I thought they might come back to give me trouble, but wisely didn't.

    Almost done repainting the back half of my bike. I made a new, improved mounting system. It clamps across the seat stays and will really help reinforce the frame. The old system used two separate mounts. I made it that way for a reason, where the rear brake would raise the roller in case of an emergency stop. But I decided against that idea. This new mount is made out of some nice 1" thick aluminum stock.

    I'll have some pics and details to post soon. Going to go apply a few more clear coats now.
     
  6. a_dam

    a_dam New Member

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    Couldn't get online for almost two weeks because of phone service. I'll hold my tongue in case some member works for AT&T.

    The old girl's been back on the road a while now. Frame welded and repainted. New beastly mount. All OK. I said I would take pics, and since I took em, I guess I'll post em.

    Pic 1: Old mounts. I'll call them pivot mounts since the motor actually is bolted to a steel plate and the motor and outboard bearing pivot together. These old pivot mounts show a bolt and nuts going through them just to hold them in the original orientation for laying out the measurements of the new mount. Old mounts were clamped to frame seat stays with 4 hose clamps. (Only using 2 in pic for illustration). The hose clamp system worked fine, but I was never really "proud" of it.

    Pic 2: Size up. Block of aluminum with holes drilled at same angle as seat stays. Getting the spacing and (especially) angle right was tricky. I have a cheap benchtop drill press and 10$ calipers.


    I'm going to upload now and make multiple posts because I still don't trust this phone connection.
     

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  7. a_dam

    a_dam New Member

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    Pic 3: Spacer out. The 3/8 inch threaded pivot rod passes horizontally through mount. I didn't want the steel rod to wear out the aluminum and get sloppy so steel sleaves (spacers) are used; 1/2 OD, 3/8 ID. They'll be J.B welded in. (Never used JB weld in my MB before, but it seems to be a popular item)

    Pic 4: Spacer in. As Ace Ventura would say; "LLLike a glove!"

    Pic 5: Clamped. Skip forward quite a bit. Block has been "split" on band saw to clamp around seat stays. Spacers epoxied in. I let them extrude beyond the edge of the aluminum the thickness of a washer, for better side wear. Then the mount block was drilled and tapped so there are 4 allen-head bolts clamping it to the seat stays with a layer of inner tube rubber for damping.
     

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  8. a_dam

    a_dam New Member

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    Pic 6: With motor rear. Pivot rod is through pivot mount. Friction roller is resting on tire. I don't know if it is my camera or monitor, but to me the colors are too bright and contrast is harsh. In real life things don't look so rusty and dirty. The rear brake, outboard bearing, springs, etc... are still off. But with everything on, especially the roller guard, it's hard to tell what you're looking at.

    Pic 7: With motor side. Hope you can tell how the motor and roller pivots on the tire.


    One more pic: On rack. She's all wrapped up with paper, bags, and saran wrap for the repainting of the back half. I never painted on a frame that wasn't stripped. Maybe as a stupid kid, but even then I think not. Bike rack is homemade from a woodworker's iron pipe clamp and some lumber.
     

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    #8 a_dam, Jul 1, 2009
    Last edited: Jul 1, 2009
  9. PatTheThird

    PatTheThird New Member

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    Wow! Anything worth doing is worth overdoing! I mean that quite seriously.
     
  10. DaveC

    DaveC Member

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    I just wonder what he did for a rear brake. It was a center pull. Today's side pull version could be added by welding the lugs to the down tubes but I'd almost bet the bike was retired from MB service but that's a guess.duh.
     
  11. a_dam

    a_dam New Member

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    This thread was over two years old. Just saw the reply in my inbox.

    I have a rear brake because, as this post was about, the frame boss for the rear brake was rewelded over two years ago.

    It worked well. I'm still motoring on that bike, with that Homelite motor. Going on my fourth year; well over 10 thousand miles.

    I'm glad that it's working without incident and I don't have anything interesting to say about it lately.

    No news is good news!!
     

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