2nd broken frame

Riiight... overstressed & fatigue due to rider "abuse" & error - but I think this topic is about the potential failures attributed to motorizing & not just throwing yourself about w/wild abandon? :p
 
I watched on TV (a show called "Greatest Disasters" or "Worst Disasters" or something) as a pro cyclist was racing down the side of a mountain on a bike with a carbon fiber frame, to set some kind of record, and he somehow broke the bike. And he paid for it, and paid for it, and paid for it, as he went tumbling down. He lived. Bike didn't. And that was carbon fiber.
 
Every body seams to want to go uber fast speeds on these bikes! I know I have. Been lucky so far. Gotta imagine paying for it and paying for it and paying for lol.
 
I saw that Allen. Scarry stuff. Alls I could think was why did he even use that high dollar, low weight frame to begin with? The extra weight of a 1960s steel (American made, God bless the US) wouldn't have made a bit of difference. He was going down hill! lol.

I have a Point Beach and am guessing it is well over 6K miles on it. Has had 2 China girls, a Honda 50cc and now a HF 79cc on her. Frame is still fine. I hope thats not a "yet" Love that dang bike.
 
ok so reading through all these post about the head tubes and drop out and seat post and even the frames near the engine cracking and breaking due to stress. what if its not just the frame cracking? instead the loss of bolts nuts premature faliure of engine. i came across a raleigh beach cruiser frame, stripped it down to bare frame flat blacked it built it back, and installed my skyhawk 66cc. within the first 25miles of break in maybe less, the vibration from the engine has completely broken my drop outs. this was the first. the second was my fenderstays, and because of those my tire. heres where it gets good. after all the repairs from prior vibration curses. rideing my boardtracker style motor bike through the neighborhoods from the shop, when all of the sudden the engine bogs down then dies. hop the curb check out the motor, one of the screws on top of the carb has worked itself out, so everytime i twist the throttle the whole housing for the throttle and choke come up. with my trusty gerber tighten the screw thats left enough to make it home. after that on the way to work about 2 days after that, the engine revs go crazy while slowing down to a stop sign. clutch arm dowel pin comes out, no clutch...got that fixed, going home the same day engine bogs out again. this time the carb itself broke, the ear that the bolt goes through to hold the carb onto the intake mani broke off. :-|| in a rage i strip the engine from that frame and strap it to a chromoly trek frame, holding the carb on with one hand, frame doesnt vibrate as bad as the cruiser....? wtf...
 
You know, as I read posts like Gip's, I'm beginning to see that there seem to be some frames that transmit engine vibes more than others; even taking into account solid engine mounting procedures, they still rattle your teeth, your screws, your bolts, and anything else that can come loose.

Has anybody else noticed that certain bike frames, no matter who builds on them, just vibrate really badly? Or am I jumping to a premature conclusion here?
 
Allen Wrench, this is my second mb. my first was a magna, which it vibrated but not as bad as this cuiser frame. i was reading other post about the gap between the mounting and frame, and also the dampners. on this cruiser frame i though it be a good idea to install pieces of rubber to kind of minimize the vibrations. but i think i did more harm than good. i took the engine off the cruiser frame and installed it on a murray frame, and it doesnt vibrate nearly as bad. i left out the rubber between the frame and engine. now im wondering if that was the problem that i created...?
 
gip said:
Allen Wrench, this is my second mb. my first was a magna, which it vibrated but not as bad as this cuiser frame. i was reading other post about the gap between the mounting and frame, and also the dampners. on this cruiser frame i though it be a good idea to install pieces of rubber to kind of minimize the vibrations. but i think i did more harm than good. i took the engine off the cruiser frame and installed it on a murray frame, and it doesnt vibrate nearly as bad. i left out the rubber between the frame and engine. now im wondering if that was the problem that i created...?
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Read the going consensus over here. http://motorbicycling.com/f6/rubber-not-27364.html
 
I think I saw that in the "How to properly mount a china-girl" thread Allen. "cause if it is a sloppy union, stuff shakes lose.
 
captainrichhill said:
I found two cracks in my Wal-Mart Point Beach which I really love. Anyone else have broken frames from the vibrations I guess? I don't know if I should be looking for a NEW frame/bike of try to get this one welded up. The other crack is a the weld where the seatpost passes the backbone.
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That's not a crack that's a complete fracture through and through. take it back to Wally world and complain, that is a fabrication error not from vibration
 
Jumpa said:
That's not a crack that's a complete fracture through and through. take it back to Wally world and complain, that is a fabrication error not from vibration
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Actually it's not its an engineering error. Aluminum is alloyed with magnesium and silicon to make it strong. That is what the 6061 numbers mean. It work hardens and get's brittle over time. Vibration and bumps all speed up the process. And it always seems to fail at the edge of a weld. A cantilever frame should be a spring from the axle all the way to the head but where it welds to the seat post it's not a spring anymore its just like putting your knee in the middle of a stick and pulling on both ends. It's gonna fail at the end of a weld everytime. It's even worse on those Panama jacks where they welded a tube in the middle of the seat stay to to rear rack. You load the rack with some weight and hit a bump guess where its going to break? Right at the edge of the weld on that rack support. I've repaired this stuff thousands of times on headache racks for trucks, irrigation equipment, all kinds of aluminum stuff the weld won't break the aluminum will. Damping the shock might help like on a full suspension bike frame but eventually that's where it will fail. If it fails. I hate aluminum imo its total garbage. You don't see aluminum motorcycle frames around do you? There is a reason for that.

But in fairness I don't think engineers thought the bicycles they designed were gonna get motors stuck on them either so really when we jump curbs, and hit potholes at thirty miles an hour with a case of suds on the back rack its sort of our fault for pushing the envelope too far. A heavier steel frame is really needed for this stuff or else you get what you get. Just pay attention and look it over often and take it easy.
 
An aluminum frame that copies a steel design for aesthetics such as a cantilever cruiser, I can see as being flawed as little concession was made to utilize the materials differing attributes - steel is more flexible, yet rigidity isn't inherently bad, that debate - which is "better" for bicycle frames, is one that's raged on w/o resolution for quite some time with no sign of ending, particularly if you include composites.

I would hazard that it's not so much the material, but it's actual quality and the engineering behind it's use, the "strongest" alloy in the world won't make up for oversights in those areas - even the engineering "oversights" that may well not be accidental as the strongest, most rigid materials are most often used with bikes that are also designed to be as light as possible - and it's that sacrifice, integrity vs weight, that has resulted in many a failure, far more so than can be attributed to the material alone.

You don't see aluminum motorcycle frames around do you? There is a reason for that.
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In fact, not only are aluminum motorcycle frames commonplace, the disagreement over which is "better" is so long-standing as to be almost a cliche, with the Japanese preferring the twin spar aluminum frames for their superbikes with Ducati being one of the few stalwarts holding out with the more traditional steel...

In the end I suspect more than anything it's important to go with something you prefer and feel safe with, ensuring only that the quality of manufacture is up to the demands of the materials used *shrug* the least expensive box store bicycles aren't usually the best examples of material utilization, engineering & design lol ;)
 
Current, supercharged, top of the line Corvettes have an aluminum frame. (Base Corvette has a steel frame). Aluminum can be strong enough for any application, but it requires the right design, metallurgy and plenty of dinero.
 
Of course aluminum can be great stuff. I have an aluminum frame schwinn mountain bike I love to ride. It's light and quick. Do I have any illusions of it being a quality tough frame? Nope. One good thwack and its toast. I know that. Would I hang a motor on it? Nope. I don't think they bothered much with heat treating the frame and then selling the whole bike to me for 150 bucks. It's probably made out of the same beer cans I emptied six months ago. Now those were some good cans. I'll get my moneys worth in fun out of it but toss it when its done and not give it a second thought.
 
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