CUT THE FRAME ? 4 heads bolt back on PICTURE only

[Piute]

                                               

[shinyribs]

Interesting.It doesn't exactly look removable,though.I wonder why they did that?It doesn't look extended either.Interesting

[MarkPBG]

Cool, take out 12 screws, remove head, no need to remove block…nice! The kits I've seen don't show pics of the upper bracket pieces. I was wondering how it would work if that one was still welded on. I knew there had to be two more plates! Thanks for the pic!

[TOOLS1]

That looks like the Cycle-X kit. I would just cut the tubes off, and not worry about it. The frames are plenty strong without them.
TOOLS

[Piute]

                I was just pulling up 77 F2 pics and ran across this and plan to do the same.
   A frame for me needs to be as strong as possible I over kill everything,if your going to lighten up the bike may be fine to be weaker but I'm pulling A trailer ,bags,fairing and will have bigger bore one day,weaker no thanks,
 I'll add bigger tubes over like this and just slide,very simple really and no reason not to have it,back on if not that hard or much cash,4 peaces of tubing couple flat peaces and good azzz drill bits/tap,All gets covered don't have to be pretty.


 
                chest has only change of cloths and towel (just looks top heavy)
                 But I've learn to appreciate the use of a trailer,you can stay up right
                               in strong winds and not get blown around
                                            AND BRING JUDOSE

[Re-run]

Don't kid yourself. for light riding, these frames are ok. But if you like to push the bike, the frame does flex quite a bit. A good set of rear shocks and some fork work help a lot to absorb things but the frame isnt that tough, at least not on the sohc. It probably won't fold up on you though.

This frame mod is excellent and I might have to get one some day.

[shinyribs]

Rerun,when i had my frame stripped down to be powdercoated i had it clamped in my vice right behind the steering neck.I could grab it at the swing arm mount location and watch it twist with my bare hands.Yes,the motor being out probably weakens the chassis,but they are really NOT all that rigid,either.Of course there are a lot of guys with cut upper tubes.You know what they say:"The proof is in the pudding". I will be leaving mine,though

[voxonda]

Hey,

I do make these frame kits. Is designed by one of your fellow Americans but I make these, in consultation with him, kits for guys overhere in Europe. In the past there where some simpler solutions although not as strong as this. In this pic both plates should be on the inside of the frame.
It is really something to be considered if you are playing with the thought of cleaning up/powdercoat or paint your frame. Makes working on your top much easier.
 
Even build it on my racer:

In my experience of working on these bikes since the early 70's it is not so much the frame, although there is somethings to desire, but the mounting of the engine in the frame that can be much better.
I designed some reinforcements for that.

[Piute]

  @ Vox yours does look a whole lot cleaner
          thanks for the info every-one,Was / is all A thought and A picture,for now.

[Peterwh]

I don't think the kit adds adds any strength.  I think once the frame is cut, unless you weld the tubes back in, the strength provided by those tubes is lost.  Putting the tubes back with any of these kits is purely cosmetic.  If you are concerned at all about the strength of the frame, I would not use one of these kits.  

[Re-run]

These kits use inserts that go into the frame tubes so the strength at those points is actually greater. The joints are also solid with no flex. The downside is the extra weight but that pales to the advantages.

[voxonda]

Hello peterwh:

Like Re-Run said, this is actually stronger than the standard tubes. Since the tube are actually shorter makes them much stronger against distortion. I run this kit for years now on a bike used mainly on track, ie. hard braking, acceleration and high corner speeds. There is not one sign of distortion or deflection. Never ever had to reset the bolts.
Believe me, if it would not be safe, I wouldn't use it.

Cheers, Rob

[Peterwh]

OK, how would you even begin to analyse the strength of this mod?  FEA is the only way you could get close for such a complex structure.  First, it will provide virtually zero torsional strength.  Second, the tensile strength is reduced to the shear strength of the bolts which, compared to the tube that has been cut, will be minimal.  Most bolted joints actually rely on the frictional force between the mating surfaces for their strength.  If insufficient clamping force can be applied, as is likely to be the case here, then you are reduced to the shear strength of the fasteners, which, as I've said, is nothing like that of the original tube.  Finally, you could never replicate anything like the bending strength of the un-cut tubes.  Sorry but I think these claims are seriously exagerated.  I'm not saying the mod will cause the frame to fail.  I'm saying do not believe that the mod will replicate the original strength of the un-cut tubes.  This mod is just cosmetic.  If you cut the tubes, I would just leave them out.

[Piute]

 Peterwh ""I would just leave them out. "" you do that

 Piute "" I believe something is better then nothing ""
   
                       ""                                                                                      ""
                           I live by Faith it wasn't just given to me I worked hard at it
                             and believe that there is more to life then just living it .
                          when you find what that is you hang on to it and any Lil bit
                             gives you strength.learn it and how to live it ...
                                                                                                Piute...

[Re-run]

Peter, the tubing is thin walled steel. Match that against grade 8 bolts and see which is stronger. Bet the bolts win by far. Second, this kit INSERTS into the existing tubes with SOLID metal. It is then bolted, with 2 bolts, into the tubing, after you have to whack it in with a mallet. From there, you use 2 bolts at EACH joint.
I know you do not want to believe this but the kit is much stronger than the tubes that got removed.

Vox knows his stuff on things like this, he runs a dry clutch on the 750 among other things. I think even a well done turbo kit. I also know the guy that designed the kit he runs and others that use this kit. It has never failed. In basis of fact, it is a strong kit.

[voxonda]

Peter,

As everyone else you are intitled to your opinion. If you would look into the construction you would see that nothing is exagerated. Second of all I take that personally and it offends me even a little bit.
There has been done some severe testing, and is a ongoing process, before I decided to replicate these kit and offer them through my site.
I believe in this kit, and so do many others. If one does not, fine with me.

Cheers, Rob

[Peterwh]

If you have to whack the inserts in with a mallet, how do you remove the rails subsequently?

[Peterwh]

Voxonda, would you be prepared to share your stress analysis and calculations. I would be very interested to see how you approached it as it's a very complex structure.  

What do you think prompted the original Engineers to put those bars in?  I suspect they were concerned about torsion as the frame flexed around the cross section and this prompted them to over engineer it to provide a wide margin of safety.

[Re-run]

Peter, the frame flexed already. It was not perfect when it was designed but was probably the best they could do...in 1969. Compared to todays frames, it would be considered barely adequate.

As for whacking it, you do not need to remove the parts. You have an insert that goes into each end of the tubes, something like 2 inches or so into each end and they get bolted in. Then you bolt the ends of these inserts together. The inserts are solid metal and so much stronger than the hollow tubes they replaced.

I would put Jesus himself on a bike with the frame kit.

As Vox said, you can certainly have your opinion but I can tell you that not a single 1 of these frame kits has failed. Adding one of these will not turn a cb into the motorcycle equivalent of a ford edsel.

[Peterwh]

Rerun, I really don't mean to offend anyone and I'm sorry if i have.  I just think this is an interesting mechanical structure.  I also think I'm being misunderstood here. I'm not saying I think a bike with this mod will fail.  Im not even saying it will be anywhere close to failing.  I'm saying that, as a Mechanical Engineer, I think a frame with the mod will be weaker than a frame without the mod.  I'm saying that I wouldn't even know how to go about analysing the strength of the frame with the mod without an FEA model because it's such a complex space frame subject to very complex forces.  I'm saying that if the maker of the mod has had a go at analysing the forces and strength of the frame with the mod I would be interested to see the analysis and calculations and how he/she went about it.  

Clearly the original engineers had something in mind when they designed the frame because, to my mind, this particular part of the frame looks very much like an after-thought to address a particular issue and they designed what is a very stiff space frame in this area, particularly noting the use of the bracket that connects the main tube to the lower two tubes.  It looks to me as if the bracket was an attempt to introduce a lot of torsional stiffness.  Why did they feel they needed to do this?

Call me conservative if you wish but I personally, would be very cautious about cutting those tubes unless I understood the strength changes that would result and without understanding what was in the designer's mind.

Regarding the strength of the original materials, the frame is constructed from DOM tube.  The cold working in the DOM process imparts a lot of additional tensile strength and I think you would maybe be surprised at how strong they are compared to, say, ERW tube.  Do we know the chemical specification of the tube eg 1010 (which I doubt), 1012, 1020 (which I suspect), etc.  If someone knows that, I can easily get the tensile strength.  You have to also remember that the bolts used in the mod are in shear (unless you  can get sufficient friction between the inserts and the frame tubes) whereas the tube is in compression/tension/torsion, which makes a big difference.  I don't think you can assume the mod has very much torsional strength at all because of the bolted design.