Broken AF frame - Do you know of any?

[Motorrad]

Very nice work. That head stay is beef

I wouldn't run stainless hardware there though.

[ylwgtr]

I'm unsure who's questions are for who here but I'll answer just incase there for me....I don't use stainless bolts anywhere....I design my parts to take genuine bolts from either one of the four jap brands...I dummy up with whatever I get my hands on but assemble using OEM bolts,the ones in the pics are s**tty steel ones(not stainless anyway).Also I don't run front headstays on any of the jobs I do

[Motorrad]

I'm unsure who's questions are for who here but I'll answer just incase there for me....I don't use stainless bolts anywhere....I design my parts to take genuine bolts from either one of the four jap brands...I dummy up with whatever I get my hands on but assemble using OEM bolts,the ones in the pics are s**tty steel ones(not stainless anyway).Also I don't run front headstays on any of the jobs I do

Cool.   they look like stainless on my phone...

[mxaniac]

Most stainless fasteners are 18-8, equivalent to a Grade 2 U.S fastener.  Don't confuse stainless fasteners with strength.  You can get very high strength fasteners in stainless but most are not.

[ylwgtr]

I like things looking like the manufacturer built them thats why i like OEM stuff....nothing worse than a dirty unflange hex bolt in my books washer or no washer

[motopunk]

just found this... looks like wrong heat treated and cracked direct at the welds between rails and y-part... 


and this pic from 2009 with the broken honda-frame..there is also a video on youtube, where you could see the bike running and little bit later it was happened... name of the video: 500 2stroke day at apex ..

[mxaniac]

Correct, you want DIN 6921 fasteners in 10.9 or 12.9 grade.

I like things looking like the manufacturer built them thats why i like OEM stuff....nothing worse than a dirty unflange hex bolt in my books washer or no washer

[mxaniac]

I'd like to have some strain gauges and accelerometers on a bike.  Pretty hard to analyse when you don't know what the inputs are.  Head stay comes up again and again, if that is the case I would assume High Cycle Fatigue is the culprit.

just found this... looks like wrong heat treated and cracked direct at the welds between rails and y-part... 


and this pic from 2009 with the broken honda-frame..there is also a video on youtube, where you could see the bike running and little bit later it was happened... name of the video: 500 2stroke day at apex ..

[mxaniac]

So a quick disclaimer, anything I state is merely a subjective opinion and should not be relied upon for anything other than entertainment purposes.  Use of such opinons for any other purpose could result in serious death or injury.  Sorry about the ridiculous disclaimer but the world is what the world is.

I modelled up a crude representation of the KX450f frame with the Y moved up in the configuration I used for my conversion to the KX500 engine.



Based on this model and a very simplistic analysis I've reached the OPINION, which I refer you once again to my disclaimer regarding the appropriate use of, that thin wall square tubing is woefully inadequate even with a very rigid head stay in the region directly below the Y.



I'm unable to submit recommendations due to liabilities so I'll leave you to your own conclusions.

[sandblaster]

Excellent work, thanks for posting!
I agree with your analysis...
I would like to ask you a favor.
Along with the back head stay, could you model in a head stay at the front like the pics below?





It may well be that thicker walled tubing is needed, but I would sure like to see the front head stay with the stress analysis ran on it..

[mxaniac]

It may well be that thicker walled tubing is needed, but I would sure like to see the front head stay with the stress analysis ran on it..

Can you get your engine in and out?  With all the cases on?  If i recall correctly the water pump is always part of the problem getting it out.

[sandblaster]

Never tried it with all the case covers on.
I have tried it as you see it and no problem.
I'll see if I have some extra case covers around and try it.

[jBernard]

awesome job modeling the frame. very impressive!
+1 on adding a front head mount and re-running the stress test. I'm really hoping on that showing some different results and taking some load right below the Y as that seems where most are breaking.
I'm running square tubing on mine  , so making a front mount right now to give me a little insurance. + heat treating it also.

[mxaniac]

For the purposes of discussion only one could surmise the front head stay significantly reduces the stress in the problem area, but not enough to be considered the only fix.

[jBernard]

awesome. thank you for doing that.

odd that by the way the stress is showing, it almost looks like its a shear force between the headstay and the top motor mount. like they are moving separately (headstay mount is moving more forward than the top motor mount).