Such sad news....

All,
After all of your help rebuilding my top end- I finally got the bike back together and was riding for two weeks.
After a long ride I came home and did my normal frame inspection, and found this on my back bone.

Sadly, I need to order a new frame and start from scratch...
My prized pose ration of a bike will have to get a total makeover and a new frame design to prevent this from ever happening again.


I'll keep you posted on the changes I make and the progress of the rebuild.
Why does this always have to happen at the beginning of riding season?!?

Glad you found the break during an inspection and not after a crash.

Yes, better to find it in the driveway. That sucks though.

They've got better frames than that one. You need a double cradle frame. A lot of stress goes into the back bone and with a 90+ HP motor in it, you need all the beef you can get. Sorry to hear this but I'm not surprised.
Steve

Well the normal kz900/1000/1100 all have a double downtube, triple tube backbone frame, should pretty much sum that thought up.

Instead of worrying about swapping frames, take that tank off, get some good pics of the whole bike and see what some of our resident fabricators think should be done (leon usually finds these type of posts) was that a stock 82 frame to start with?

Miller had a S&S frame meant for a Harley. His Honda/Davidson was pushing 130HP. He didn't have any problems but that was in the 70/80's. Those frames were made for go and show.
Steve

That sux. I wonder.. Rather than a complete redesign, if a slightly larger diameter down tube and a much larger diameter backbone and maybe some small gussets at that joint would solve the problem?

I've seen a lot of Choppers come and go. Most are for looking at not riding every day like most of us here. There's a fine line between being too much or too little. Add a extended front end and a hard tail, that frame is taking all the stress and flex. I'm afraid that frame was under designed for the power and weight. Might be able to beef it up some but that would change the look.
Looked great though.
Steve

Wow such a cool bike, love the fuel tank. Sorry to see that.

Could you not replace the top tube with something bigger diameter and fatter wall thickness?

Extra bracing and gussets all round with the frame in a jig, done by a shit hot welder who really knows custom frames?

I think the crack is symptomatic of a highly stressed area, inherent in that extreme frame design.

It's the gooseneck, for sure.
The new frame will be a double downtube.
I hit a big bump, and all the frame tries to do is straighten the single down tube, and it pulls the station bar away from the back bone...

And I should note- this has happened twice before.
Counting the original mockup I have built this bike and torn it down from the ground up 4 times. As in, not once, not twice, not three times- but 4 times!!!
If you point to any bolt- I can tell you the pitch and length of every damn fastener on the rig.
It's great that I can do so- and I've learned so much while doing it.
However- is it necessary? No. Not really.

Only four times? my first big GPz550 project was like that...motor in and out about five times, carbs off about 10 times tuning them. I learned a lot from that, 20 years later I'm a bit better at it now.

Keep at it man. When you dig really deep great things happen where mere mortals would have given up long ago. That bike is very cool.