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Very interesting discussion and contributions by folks that know a LOT more than myself.

That said, I'm very interested in the bolt-on brace. I have a white frame free of cracks, and, at this age, not hard on the thing, but I also plan on keeping forever. I'm not terribly interested in stripping the bike down, but some added (or in this case bolt-on) insurance is very intriguing. I'm seeing differing versions on transfer of stress. Is this worthwhile? And if so, where do I get the brace?
 

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Very interesting discussion and contributions by folks that know a LOT more than myself.

That said, I'm very interested in the bolt-on brace. I have a white frame free of cracks, and, at this age, not hard on the thing, but I also plan on keeping forever. I'm not terribly interested in stripping the bike down, but some added (or in this case bolt-on) insurance is very intriguing. I'm seeing differing versions on transfer of stress. Is this worthwhile? And if so, where do I get the brace?
Those BBB Fab braces are $80.00 USD, shipped from UK. I bought mine straight from Steve (the fella who makes them in England) .... here's his eBay ad for the brace ....

LINK = https://www.ebay.com/itm/Ducati-SS-900-750-600-Frame-brace-/153744414592?hash=item23cbe19780

Is it worthwhile? .... Certainly can't hurt!
 

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Not so Neil. People have posted quite a few frame cracks here on braced frames. Frame then cracked at the end of the new brace. The stress riser was moved, but not eliminated. Do a search, don’t take my word for it.
Then they didn't do it properly, can't be bothered searching tbh but betting they put bending loads into the middle of a section & didn't triangulate properly, nuff said.
 

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Then they didn't do it properly, can't be bothered searching tbh but betting they put bending loads into the middle of a section & didn't triangulate properly, nuff said.
So many times I've seen situations where someone didn't know the difference between tensile strengths and column strengths when they design added bracing to an existing space frame. They'd add in cross bracing in a tensile configuration when it should have been in a column situation ... or vice verse. "Just start adding metal, that will work fine!". ?
 

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This is the only motorcycle frame I’ve ever seen crack after the steer head area was braced. I’ve usually seen dirt frames reinforced in the steering head or swingarm area with no issues.
Raked choppers too. Even those spindly Penton and Bultaco frames didn’t crack after being reinforced. Though the welding technique may very well have contributed to the failure, I think the tubing they used should have been chosen based on the welding methods they used, or else the welding method should have changed based on the tubing. Most frames flex, but most frames don’t crack.
 

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This is the only motorcycle frame I’ve ever seen crack after the steer head area was braced. I’ve usually seen dirt frames reinforced in the steering head or swingarm area with no issues.
Raked choppers too. Even those spindly Penton and Bultaco frames didn’t crack after being reinforced. Though the welding technique may very well have contributed to the failure, I think the tubing they used should have been chosen based on the welding methods they used, or else the welding method should have changed based on the tubing. Most frames flex, but most frames don’t crack.
Well, that's what happens when things are engineered down to cost. When the bean counters have say over the engineering department, shit gets stacked on top of shit. And you end up with a large pile of shit. Cracked shit.
 

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i don't think any of what the factory did could be called bracing. more "we're going to put this tank hold down bracket mount here no matter what, and we're going to do it until it works". the fact it's on the bending load surface, not the load centreline, certainly wouldn't help. the cross brace ala the 851/888 frame still allows the head to move to some extent, but like the lower tubes they now can't spread out to the sides, as they would if completely unrestrained.
 

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I was referring to frames people have added extra bracing to that subsequently cracked just beyond the new brace. Just looking at the factory tank mount I would believe the factory thought it was going to strengthen the frame when they designed it. I’ve seen some frames where people redesigned the mount in an attempt to reduce cracking.
 
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So with all of this kicking around of heady reasons about why this, why that, and second guessing what/why the factory did XYZ .... what is the best answer to prevent the problem?

1) - preventing cracking on a frame that is undamaged.

2) - preventing further cracking on a frame that was damaged and repaired.

Just saying the frame was poorly engineered doesn't get us anywhere. We already know that ... the cracked frames shout that loud and clear. What is needed are solutions. I have my own ideas in that regard but hearing what others have to say is more important to me ... I can listen to my own ideas rattle around in my head endlessly .... I'd rather get some new input ... I'm all ears!
 

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So with all of this kicking around of heady reasons about why this, why that, and second guessing what/why the factory did XYZ .... what is the best answer to prevent the problem?

1) - preventing cracking on a frame that is undamaged.

2) - preventing further cracking on a frame that was damaged and repaired.

Just saying the frame was poorly engineered doesn't get us anywhere. We already know that ... the cracked frames shout that loud and clear. What is needed are solutions. I have my own ideas in that regard but hearing what others have to say is more important to me ... I can listen to my own ideas rattle around in my head endlessly .... I'd rather get some new input ... I'm all ears!
well, in post #8 i said

" i would remove the bosses welded to the frame that the tank hold down bracket mounts to, to allow the frame to flex as it wants to, and make another bracket to hold the tank down. i welded a threaded boss to the back of the steering head (down lower) on my 93 frame to fix a tank hold down bracket. "
 

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What is the frame made of? I was under the impression that it was made with chromoly, but is that right?
 

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I noticed the exact same thing in the front end feel first ride out after making the modifications to my frame Apexdc.

The frame felt more solid and unified and the steering felt overall more precise. I also noticed a bit more road feel up through the bars too. My hands felt more connected to what my front tire was doing.

I have to admit the bracing that you've added to your frame looks so much cleaner and nicer and factory than what I did to mine. Well done sir.
Thanks so much. I wish I could take more credit, but I know a REALLY good welder. That helps.

I have had the bike almost twenty years now and will never sell it. Decided to do a full restoration a couple of years ago. It was my first try at this level, but took my time and had huge fun with it.

These are great bikes! Not state of the art any more, but in another twenty years, they will still be cool old Italian motorcycles.
 

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well, in post #8 i said

" i would remove the bosses welded to the frame that the tank hold down bracket mounts to, to allow the frame to flex as it wants to, and make another bracket to hold the tank down. i welded a threaded boss to the back of the steering head (down lower) on my 93 frame to fix a tank hold down bracket. "
Apologies .... I obviously missed that.

However that seems to be countering what others in this very thread have said ... including Member *Stoshmonster's solutions, as well as what Member *Apexdc hod done to his frame.

There does not seem to be a consensus about what the best way to deal with the issue is. My own perspective on it is to either install the bolt-on brace, or to bronze weld in bracing rather than welding any further cross members or bracing in. That would add strength while at the same time permitting flex ... much different from welding (as in fusing metal) in reinforcement.

Just yet one more opinion on the matter.
 

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My guess on why they crack is that if the bike is coming down from a wheelie and lands relatively hard, the top of the steering head would try to pivot to the back of the bike. This force would try to move the frame apart at the point where the normal brace was eliminated and hence, the crack. If the brace is there, the steering head would not be as free to rotate.

Just my theory....
 

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My guess on why they crack is that if the bike is coming down from a wheelie and lands relatively hard, the top of the steering head would try to pivot to the back of the bike. This force would try to move the frame apart at the point where the normal brace was eliminated and hence, the crack. If the brace is there, the steering head would not be as free to rotate.

Just my theory....
Same forces are applied under hard braking with the front brake, only difference being the bottom of the headstock is pushed back ... a wheelie landing pushes the bottom of the headstock forward. Both actions try to move the headstock around, creating stress on the area.
 

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Same forces are applied under hard braking with the front brake, only difference being the bottom of the headstock is pushed back ... a wheelie landing pushes the bottom of the headstock forward. Both actions try to move the headstock around, creating stress on the area.
Very true. Braking would be trying to bring the top frame tubes together. Both actions over time would be flexing the area around the headstock back and forth. Not good for sure.
 

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What is the frame made of? I was under the impression that it was made with chromoly, but is that right?
That’s my understanding too, but you have to realize chromoly is a family of alloys, not just one. Same with “stainless steel”. The various alloys have different properties. The wrong alloy may have been chosen, or at least one that was not optimum for the job. The supplier of the raw material may not have provided steel that was free of NMI, non metallic inclusions. In other words, dirt in the steel which later starts a crack. On top of that, the biggest problem could be the tubing manufacturing process. Stress could have been introduced into the tubing and not properly relieved, that later resulted in failure.
 

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we did quite a lot of frame repalcements under warranty. i think we did one 750, no 600. all of them have similar soft fork springs, but the 900 showa adj forks have much more high speed compression damping, more engine torque to load and unload the front end, but the same front brake.package as the 94> 750. albeit with an arguably increased need for hard braking compared to the 750 due to the increased performance.

in the uk desmodue series, where 600ss got twin discs and typical race use, they cracked consistantly too i'm told.

if there wasn't the airbox access issue, you'd just weld in a top cross bar like an 851. as per apexdc's in post #29.
 
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