Maintenance & Technical > KX500 Aluminum Frame Conversion (AFC)
JFab frame rails breaking
sandblaster:
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.
jBernard:
^ 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?
don46:
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.
kxpegger:
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.
jholt:
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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