Maintenance & Technical > KX500 Aluminum Frame Conversion (AFC)
my poor bike
jBernard:
this is surprising, ive seen some pretty smart people say the lower cradle(rails) hold very little weight, and most of the rigidity is between the headstay and the swingarm bolt.
if it broke below the Y, is it right on the weld? that may indicate a bad bond between Y and new frame rails.
mxaniac:
mxaniac:
Angled breaks would indicate tension in AL. The straight across breaks are right past the weld beads indicates either lower strength material properties or stress concentration from the weld beads (or high shear forces). Since the left side didn't even break near the weld I would guess material properties at the actual weld were fine.
I think it's all in the motor mounts. Too stiff without enough flex in the remaining material. Bending creates tension and compression, not any appreciable shear.
jBernard:
thanks for the pics. thats a real interesting break, and looks like youre right in how it broke. looks like the engine got pulled backwards and just seperated itself and the rails from the static Y.
what does your headstay look like? it almost looks like the engine tried to move back 3/4" violently, cant really see how it did that with a solid headstay mount enough for it to straight shear off like the pictures show.
who did your heat treating? not to knock them or say they had anything to do with this, just i only have 1 source so far and they are $$$.
sandblaster:
Because a few people had problems breaking their frame rails I wanted to be sure I understood where the transfer of energy was taking place at.
Here is a rough diagram of where the mounting points are in relation to the frame.
As you can see, when coming down hard on a jump the force is transferred in a radial motion pivoting on the 17mm swing arm pivot pin.
So, the rear head stay must be in line as much as possible with the direction of the force to prevent the engine from rotating forward and putting the frame rails under tension.
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