JFab frame rails breaking

[jholt]

I dont know exactly what really caused it but I just didn't have time to repair and try again so last night I sold it.  It was alot fun but I think I will stick to a stock machine for a while.

[suicyde]

^ do you know exactly where it broke?
i cant say ive seen a stock frame rail ever brake. obviously they are forming them in a less stressful way and probably heat treating after welding. something to consider since i'm surprised no one has gotten injured yet. pretty scary.

It broke just below the gusset, above the engine mount. it was vibrating like crazy, thats how he knew it broke. When the engine shifted, it broke the exhaust pipe as well. Not sure how or why, but he said the scariest part of that bike for him, was the false neutrals the bike had in third. it would skip out of gear under hard acceleration in third, then jump back in. when the frame broke, it was just the final nail. He still talks about it, misses it sometimes. Im not sure if braking the down tubes could cause a wreck, but it is still a cause for concern.

[KXDINO]

Just seen another cr500af snap in half on facebook ,that a few now.It seem to stem from the modified frame?A few extra gusset to be on the safe side might save a trip to the hospital.I had a yamy it175j break at the front downtube ,would have kept riding it to until someone pointed it out,that model was known for that,we pushed it back together and welded and gusset the area without further promblems.So for piece of mind i would strengthen this area;s

[Starky307]

This why it broke.

This headstay design had no strength in it. You must use a 3 point triangle system to make it rigid or else it will allow the motor to rotate on the swingarm.

[brooksie]

I'm right in the process of getting my frame done very soon (250F). So thanks for posting this failure.

Regarding the break, I've never liked the idea of welding the front mounts directly to the frame rails. I''ve insisted on having tubes welded through the rails and then mounting the engine with plates. It's more complicated and time consuming, but I only want to do the job once.
Also, I'm going to re-use the original top motor mount which had to be cut off to get the engine in. It will have to be shortened but I really like the triangular bracing for rigidity.
As previoulsy mentioned, I think that's where the problem started with your failure.

[maddoggy]

i can't believe that jfab never replied with his thoughts as to why these rails broke. JFAB?? this site has gone to heck

[jBernard]

everytime i called him trying to buy stuff he sounded insanely busy. i understand that making mx parts for forum guys is what he does on the side, but a simple 'hey, swamped right now, probably not going to be able to do anything for several months right now' would be more understandable than  'sure, i'll call you back next week when i get frame rails bent up' then never does.  again, nothing against the guy, seems very nice but i'm sure getting on the forums while he is up to his neck in fab work isnt on the top of his priority list.

[don46]

check out this youtube video, this guy seems to believe the headstay (which many of you pointed out) is the culprit, and after listening to his logic it does semm somewhat sound. I do believe there are harmonic vibrations at work as well, but maybe there is something to the headstay, his is super beefy and also multi point attached.

http://www.youtube.com/watch?v=zgJTHBQO4bM&list=UUbcAUzRKwwsnUu183ATJ_Aw&index=1&feature=plcp

[Motorrad]

everytime i called him trying to buy stuff he sounded insanely busy. i understand that making mx parts for forum guys is what he does on the side, but a simple 'hey, swamped right now, probably not going to be able to do anything for several months right now' would be more understandable than  'sure, i'll call you back next week when i get frame rails bent up' then never does.  again, nothing against the guy, seems very nice but i'm sure getting on the forums while he is up to his neck in fab work isnt on the top of his priority list.

You nailed it.  If you all read the first post of any of his for sale threads.  He specifically requests to be called at the shop since he is swamped..

Sorry you feel that way maddoggy.  But I have to disagree.  As we have sorted some of the frosted flakes out of our bowl of cheerios.  Everyone here currently is here because they love the K5, from guys just looking to change the oil, to some darn good tuners...

[maddoggy]

i'm not trying to beat the guy up about his rails. i highly doubt that the problem had anything to do with jfabs rail construction. pretty clear that it is a bike design torque issue. just thinking that as a businessman he would want to post up his opinion. i know he logs on and must have seen this thread. 

[maddoggy]

check out this youtube video, this guy seems to believe the headstay (which many of you pointed out) is the culprit, and after listening to his logic it does semm somewhat sound. I do believe there are harmonic vibrations at work as well, but maybe there is something to the headstay, his is super beefy and also multi point attached.

http://www.youtube.com/watch?v=zgJTHBQO4bM&list=UUbcAUzRKwwsnUu183ATJ_Aw&index=1&feature=plcp

i was thinking about dons post, specifically the part about harmonics. this may sound stupid but have any of you conversion guys ever considered using a dampener on your frames? i was thinking of the kind that compound archery shooters use. not sure exactly how to use it, but in theory it would arrest the harmonic vibrations generated in the frame. just a very rough thought.

[maddoggy]

nothing?? guess it's another of my stupid ideas

[kxpegger]

nothing?? guess it's another of my stupid ideas

I would think that JFAB might want to explore this issue and make a comment but I personally don't think his rails had anything to do with this failure. The head stay to the frame connection was improperly designed by the OP IMO. If you scrutinize the pictures you can see the flaw.

[sandblaster]

nothing?? guess it's another of my stupid ideas

I don't think your idea is stupid.
However, I'm working on a different idea to see if I experience any problems.
If it works, I'll post what I did.

[Motorrad]

nothing?? guess it's another of my stupid ideas

actually maddoggy... I have been thinking about this since you posted it..    looking at my buddys $$$$$$$$$$$$ compound bows.    (he is a sponsored shooter)..    trying to think up a way to graft it over to the bike world...


so another stupid idea ... NO..     somthign that has had me thinking for several weeks.... YES!     YOU ARE IN MY HEAD

also been looking at my "specialized Roubaix"   bicycle..  that is designed to race the cobble stone streets of france..     with dampers molded into the frame..       trying to think of a way to move that over as well..