my poor bike

[don46]

Not my intent to piss you off, just offer what little knowledge I  have. yours is the most catastrophic failure I have ever seen. I have seen cracks but never a frame that has snapped in half. Part of the issue is that most people aren't jumping the 500's regularly. I suspect that your frame was not heat treated after welding, and that perhaps the aluminum integrity was compromised. I wouldn't give up on your project, but I would use the radiused tubing and I would probably gusset that area, and lastly I would heat treat it. Lets be realistic, these bikes are jumped, cashed and crashed in the original form with nary a frame failure, so they are up to the task if we do it right.

In one of my other post I also mentioned the harmonics, maybe there is something with the 250 that we don't see with the 500

[LundMx]

i did not heat treat my KX500af because i could not find any info on it/ i.e. temperature and duration of treating, also since the engine cradle in 90% of these builds are the only part fabricated, wouldn't gusseting be just as effective however just not as visually striking? for that matter, how much time was on the bike since the conversion? the aluminum i used looks similar as yours  we have put probably 9 hrs of testing on mine as of yesterday and i inspected after riding still no visual signs of fatigue. i might try gusseting as a fail safe at this point

[KXDINO]

Kawasaki would of release there first kx450 in 05 if it was not for frame failure so they soughted the bugs out first ,06 was pretty good ,but i have seen a 250f ,i think broken in half ,loose engine bolts ,loose steering stem does not help either ,i saw a kx250 04 2 banger crack at the top spars ,tank and seat juntion witch i put down as loose bolts ,i saw a pro frame 97 i think had a small crack at top shock mount but that had a zillion miles and jumps on it.Now yamaha s have had many frames crack all alloy ones to ,late models as well,yz 450 comes to mind ,front downtube ,this was in mxa mag ,it was a manufacture fault ,plus the 2 stroke model i saw had a massive crack where top tube meets the side tube ,another place is down neer the footpegs.If the factorys have trouble ,imagine the poor guy trying to do these mods are having ?Extra gussit guys and correct technique and materials is needed .I remember the 1980 kxs had frame breakage in a big way ,and you could get a gassit kit to solve the promblem as well as a another frame with a different part number most likely the same frame with the gassit all ready installed maybe?The 81 kx seem to be ok.

[cmotodad]

I do some work at a heat treating-forging facility. I spoke to the manager and with all the inserts and different types of materials (on Honda frames the castings are different materials than the rails and Y) it would be very difficult to heat treat a frame. He mentioned something about stress relieve but it could change too much of the material characteristics. Just passing along what I was told.

[cmotodad]

After looking at the photos again,what if we plug welded solid inserts in the rails where the rails weld to the frame top and bottom? Seems like the cracks we have are always just below the welded areas.

[LundMx]

That would look cleaner than gusseting, however hacking it back apart to do that doesnt sound like much fun   

[cmotodad]

I was thinking of anyone doing a new conversion

[motopunk]

thats what i say again again and again... welding aluminium frames is not as half as easy as welding steel frames.. 

the right heat treating is important in all cases of welding to get the perfekt stability . in case of no or wrong heat treating it will break like glass right beside the welds , where the molecular chains still not arranged properly.
 the same can also happen with steel when it was not welded properly, resulting in too many stress material left and right of the weld.
with heat treating before and after the welding you will allow the molecular chains to arrange properly, to make flexible material. cause when the molecules sitting too close together, the material is too stiff at this point and breaks sometime. that's the whole secret.

[brooksie]

I think gusseting will just move the problem. You'll still have huge heat cycles concentrated in the weld areas, except now you'll have more welds/more heat cycles. It seems this type of failure won't show up until it fails, which is typical of cycle fatigue.

[LundMx]

well than what is the right answer to this? since no one seems to know the temperature and duration of the heat treating and guesseting will only move the problem then what? sh*t can the square tubing and start over with radius tubing? or even a delta box tubing~ if obtainable

[LundMx]

for that matter i will email Aj and see if he can shed any light on this matter. i.e. the heat treating process

[LundMx]

http://www.speedymetals.com/ps-2498-170-1-sq-6061-t6511-aluminum-extruded.aspx

this is what i used. not sure if it's all the same

[LundMx]

not hijacking this thread, but i wonder how hexagon tubing would work? http://www.speedymetals.com/ps-2402-53-1-x-0-hex-6061-t6511-aluminum-extruded.aspx

[jBernard]

you used solid 1" square rod?

[LundMx]

Nope, didnt notice it was solid