KX Riders
Maintenance & Technical => KX500 Aluminum Frame Conversion (AFC) => Topic started by: jholt on July 09, 2012, 01:46:45 AM
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Any one having any issues with lower frame rails breaking on their 500af. Mine broke this weekend while racing motocross, they broke about two inches down from the "Y" section.
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Do you A/F guys heat treat your frames after welding?
Did the frame rails break at a weld, or close to a bend?
Do you have photos?
I don't have an A/F bike, but I'm curious anyway.
Thanks!
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Mine was built by Service Honda. Don't know what their process is but I've beat the snot out of mine in the Nevada desert and no issues yet (4 years). I know welding aluminum is a tricky business. The metal has to be cleaned spotless and from what I have read it needs to be pre-heated to avoid bittleness and hardness while welding. There's also the type of aluminum, rod filler and amperage while welding to consider. A lot of welders can make it look pretty without really knowing what they are doing.
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I bent my own rails out of 6061 if i remember right and had them welded about 6 months ago now. Now Im no A motocrosser but I did have my cousin who is race it a couple of weekends ago at one of the roughest track here in michigan and no problems and Ive rode a few enduros and harescrambles with the same results and I did not heat treat the frame
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(http://i135.photobucket.com/albums/q156/holtre1/KX500031.jpg~original)
(http://i135.photobucket.com/albums/q156/holtre1/KX500030.jpg~original)
(http://i135.photobucket.com/albums/q156/holtre1/KX500029.jpg~original)
Did not heat treat they broke right above front motor mount and right below the upper bend I have motocrossed this bike for about 3-4 months
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Just thinking out loud here.... I'm wondering if when the motor mounts were positioned if perhaps too much of the weight was positioned on the carriage and not enough on the head.
It seems to me that a balance should be maintained.
I'm getting ready to build my engine mounts for my AF and had considered this a possible problem.
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^ i agree with the above.
looks like the weight of the motor tried to torque back and basically pulled the bottom rail section away from the top/yoke.
do you have an upper headstay mount to help distribute some of the weight?
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I don't know about weight, the motor is positioned through the swingarm bolt, and two sets on the cases, I also wouldn't want the head to be supporting a significant amount of weight as it may cause some distortion to the head causing it to leak. I believe jholt said they broke right above the upper motor mount, so the frame should have been supported at the Y and at the upper mount, to me it would seem that the failure was more of a structural issue, ie vibration, break at the end of a weld or perhaps wrong material. The first one I built I had a crack, re-engineered and no further problems, the second one was like the first redesign and no problems.
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It looks like your frame rails curve inward and were directly welded to the main spar but it is hard to tell from the pictures. If this is the case I think you lose some structural integrity because it's a longer distance for the frame rails to try and support. More leverage torsion, compression, lateral and strain forces work hardening the metal and causing fatigue stress on the rails. Just my guess? Here's a pic of how SH did it on mine.
(http://i155.photobucket.com/albums/s301/peteegger/KX500AFFrameRails.jpg~original)
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(http://i135.photobucket.com/albums/q156/holtre1/2011KX500Build038.jpg~original)
(http://i135.photobucket.com/albums/q156/holtre1/2011KX500Build032.jpg~original)
here are a couple of pics of the head stay and how the "Y" section was welded together. I did it like the original 08 kx 450 frame was the only difference is its 3 inches longer than stock.
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On my bike I used the same style headstay mount as yours accept added a extra tab linking the round cross shaft to the lower engine mount bolt holes.The reason for this was looking at it made me think the motor would pull down in the frame with nothing stopping it from rolling forward. Just my .02
If you look on the last page of my build it shows a pic
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After looking at your pictures I'm convinced that it is your headstay design that put to much stress on the frame rails. It is not a straight tight pull. It is a scissor that will allow forward and down movement of the engine. I would post a pic of how they did my SH but to get a good view I would have to pull the tank. Anyway they welded a very beefy mount to the cross spar of the frame not the perimeter frame tabs that the 450 engine used. The way SH did it there is absolutely no way the engine can rock forward and down unless the head stay of the cylinder head breaks or the frame cross spar or weld breaks. This area was very well over engineered by SH. I'll try to get you a pic tomorrow as it is about 120F degrees in the garage right now and I'm not in the mood to set up the portable swamp cooler. I live in Vegas!
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My brother in law broke his service honda frame as well, he is a pro class mx'er. that af got manhandled, and it didn't hold up. It got patched up, and sold off.
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^ 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.
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The tubing looks kind of thin does it not? I like what ktm does,4130 and lighter than any aluminum jap frame out there;plus there more room to work on where carby goes etc.
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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.
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^ 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.
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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
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(http://i135.photobucket.com/albums/q156/holtre1/2011KX500Build038.jpg)
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.
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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.
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i can't believe that jfab never replied with his thoughts as to why these rails broke. JFAB????? this site has gone to heck
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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.
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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
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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...
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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. :|
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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.
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nothing???????? guess it's another of my stupid ideas
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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.
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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.
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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! 8-) 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..
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I wonder if JFab is going the way of Stewart......
This post has been active over a month with no reply from him ????
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as noted before, guy is super busy and i doubt he is ignoring this thread if he has seen it by any chance.
there are to many other factors to put blame on jfabs rails. yoke design, welding expertise, swingarm thru bolt squareness, head bracket design to frame, ect.
people bend aluminum tubing every day and put structural loads on it. jfab's rails arent bent with any crazy angle, so i'd be looking to other stresses as the culprit as of now.
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I'm with you jBernard.
As a business owner I know that responding to every potential complaint can be tedious and time consuming.
I'm certain that this thread has been on his mind but think about it this way.
What can he say that will prove or disprove the concerns raised here?
Have you ever heard of any of his frame conversions failing?
I haven't, but like many others I chose to try it myself because I was too cheap to pay for a first class job and I wanted to see if someone as inept as me could do it.
Remember he does not make the basic material.
All he does is cut it and bend it.
It is up to you to know what you are doing and do your own engineering (Not WAG engineering).
If you run a stress analysis on the material you will see that it is more then enough material to handle the load providing that the load is correctly divided on it's mounting points and providing the head stay is properly engineered.
From the pics I saw there are problems with that design.
I'm not sure that comparing this situation to that of Stewart is really relevant.
I'd like Stewart to sign up under a different name so he can provide his technical expertise but, I would not buy from him :-)
I will be doing another conversion after I get my current one done and I will buy another set from Jfab :-o
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I'm with Sandblaster, there was/is nothing wrong with the frame rails. It was the design of the headstay that caused that failure.
I don't know jfab nor have I ever had contact with him. I can't stand seeing an internet flaming or lynch mob in action when there is absolutely no need for it.
Can someone put this thread to bed, I think it is terrible that there are people trying to put blame towards the person who bent the rails and not that of the person who didn't know what they were doing when they made the head stay.
Rant over.
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I wasn't going to post on this topic but in the end I see a good person being slammed. there was nothing wrong with the frame rails, there are many people on this site using them. What does that mean, it means that the installer failed to make a proper installation. What is it that those of you keep saying where is Jfab want him to say? he bent rails and the consumer installed them, so figure out what your problem is and fix it. It is so easy to right away blame somebody else for our mistakes. I think that it is a matter of time and you will see more break, not because they are weak but improperly installed. I had a set fail (not Jfab's) and upon reflection I re-designed my installation and haven't had one problem (I did a 250 and a 500). Remember the 500 vibrates alot, how many have broken mounts on their steel framed bikes, so the AL will probably break as well unless you have a well balanced motor.
So lets stop asking where Jfab is and fix the underlying problem, and when you do let the rest of us know how you did it so we can re-enforce our designs.
have a good day!
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I wasn't going to post on this topic but in the end I see a good person being slammed. there was nothing wrong with the frame rails, there are many people on this site using them. What does that mean, it means that the installer failed to make a proper installation. What is it that those of you keep saying where is Jfab want him to say? he bent rails and the consumer installed them, so figure out what your problem is and fix it. It is so easy to right away blame somebody else for our mistakes. I think that it is a matter of time and you will see more break, not because they are weak but improperly installed. I had a set fail (not Jfab's) and upon reflection I re-designed my installation and haven't had one problem (I did a 250 and a 500). Remember the 500 vibrates alot, how many have broken mounts on their steel framed bikes, so the AL will probably break as well unless you have a well balanced motor.
So lets stop asking where Jfab is and fix the underlying problem, and when you do let the rest of us know how you did it so we can re-enforce our designs.
have a good day!
I have made a AF my self with some advice from Jfab and AJ Wagner from service Honda. Frame braking is always on my mind (especially now) but if it does. It's my problem. This these is like the prox, wossner, wiseco piston topics. Give the product you used the fauld, not who installed it. Jerry Jfab has been "away" for a wile like me, maybe even longer because of to much work and others.
I trunned my crank with zero tollorance when I rebuild my engine this summer.
Helped allot with vibrations. And also remember that we do things that wasn't ment to be. Kawasaki R&D for months, we once and than race it!!!!
Dutchie
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Like everyone said... the rails arnt to fault.
Jerry even told us he would be away for a while. as his shop had #1 priority. Not like he slithered off into the bushes, he told us!!
I debated removing him from the vendors at that time, but my conclusion was..
why ?
you can call him on the phone, and he answers, and provides his product that way... if I removed him, then no one would know of these products, that make their AF conversions that much easyer..
I know if I was doing one, Id want to know about some guy like Jerry providing parts. even if I had to pick up a phone to get them, not just send a PM.
have any of you actually called him and asked him about them breaking?
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i don't blame jfab one bit for the rail failure, i would just like to see his input and what his advice would be. does he already have measurements and proven angles in mind? just a quick, hey this is what i think happened and here is what i would do differently on the design.
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FWIW, I know I won't hesitate to buy and use his rails when I start my conversion.
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i don't blame jfab one bit for the rail failure, i would just like to see his input and what his advice would be. does he already have measurements and proven angles in mind? just a quick, hey this is what i think happened and here is what i would do differently on the design.
Exactly...I don't care how "busy" he is. He is on this site almost daily. I'm not saying his rails are bad, i'm sure it was a bad install. ....but based on the lack of any response why would any one feel comfortable doing business with him?
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daily?
just for clarification last time he was on this site was over 2 wks ago and it was at 1AM.
i think you may be putting to much emphasis on JFabs rails for this guys complete build. Jfab just bends the aluminum rails. and from what i know about bending square tube, he has a pretty nice machine to have the radii looking like that, so its definitely not a hack job.
jfab doesnt make the motor mounts, he doesnt make the headstay, he doesnt make the yoke, he doesnt weld, he doesnt fit, he doesnt give instructions on the fab work. we havent singled out what the issue was that caused the problem, so calling out 1 particular thing is jumping the gun a bit i think.