Maintenance & Technical > KX500 Aluminum Frame Conversion (AFC)

JFab frame rails breaking

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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:

--- Quote from: jBernard on July 12, 2012, 06:22:51 AM ---^ 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.


--- End quote ---
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:

--- Quote from: jholt on July 11, 2012, 02:35:54 AM ---

--- End quote ---

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.

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