Topic: Can you cut the Center-stand cross tube out of the frame?

[Kong]

I was looking at my '77 550k frame with an eye toward weight reduction.  I do not expect to retain the center-stand on the bike and so I have no use for its mounting tube, the one that transverses the frame below the swing arm.  Its a big chunky hunk of metal that must weigh as much as a full grown chimpanzee (tree-loving twerps that they are).

So I'd like to cut the tube out of the frame, and that would be easy enough to do, but then I took a better look at it.  I'm not sure if that tube provides frame stiffness required by the bike or if the engine cases, which mount nearby, provide all the stiffness needed in that area.  So it might be a very bad idea to remove it.  Another possible concern is that it may simply be needed to maintain spacing and stop any crush of the swing-arm bushing were someone to over tighten its axle/bolt.  That said I'm sure 100's of them have been cut out over the years, and so there's probably some history out there too (though my searches haven't disclosed an stories about it).

Anyone got any thoughts on cutting it out?

[nickandkristy02]

i would say if you cut it out that the frame would end up like a pretzel

[wildcatmahone]

Sure you CAN cut it out but which would you rather have a couple pounds shed off or a weakened and flexing frame? Cut out all those banana's your eatin' if you wanna lose some pounds of your machine. SOHC Honda frames need more stiffness not less IMHO.

[swellguy]

With my new 4 into 4 exhaust setup, I had to lose the center stand. It comes of remarkably easy and quickly. I left the two mounting tabs on for now but they do look kind of weird just sitting there. I'm going with a box swingarm so once the stock one comes off I'll cut and grind the tabs off. I can't see any point in going farther than that. I don't know of you even can.

[crazypj]

I

 it might be a very bad idea to remove it. 
 That said I'm sure 100's of them have been cut out over the years, and so there's probably some history out there too (though my searches haven't disclosed an stories about it).

Anyone got any thoughts on cutting it out?

 I think there is a very good reason you haven't found any information, in all probability, NONE have been cut out (or if they have rider hasn't been around long enough to tell anyone it's a bad idea  )
 It's a pretty flexy frame in my experience, you want to weld some bits in in various places

[SilentSteven]

With my new 4 into 4 exhaust setup, I had to lose the center stand. It comes of remarkably easy and quickly. I left the two mounting tabs on for now but they do look kind of weird just sitting there. I'm going with a box swingarm so once the stock one comes off I'll cut and grind the tabs off. I can't see any point in going farther than that. I don't know of you even can.

That's what I did for my 750 K1. I removed the swing arm and the center stand. I then cut off all mounting points and grounded it down so everything is nice and smooth

[scottly]

I would leave the frame member, as well as the center stand tabs. The heavy center stand can easily be replaced for service, and removed when not needed. There are other ways to reduce weight without sacrificing any strength. 

[KeithB]

The cross tube on mine was damaged and weakened by acid from the battery over flow .
When I took the frame to a machinist friend who works on bikes, he could have told me to just cut it out but instead, welded in a new piece.
 I suggest he understood that it should be there.

[crazypj]

That's what I did for my 750 K1. I removed the swing arm and the center stand. I then cut off all mounting points and grounded it down so everything is nice and smooth

 Are you a structural engineer?
 In my experience CB750 is a bit sloppy in handling, removing frame bracing should really 'improve' things 

[Retro Rocket]

That's what I did for my 750 K1. I removed the swing arm and the center stand. I then cut off all mounting points and grounded it down so everything is nice and smooth

 Are you a structural engineer?
 In my experience CB750 is a bit sloppy in handling, removing frame bracing should really 'improve' things 

PJ, i think he is referring to removing the tabs for the stand not the actual brace.....

Mick

[SilentSteven]

PJ, i think he is referring to removing the tabs for the stand not the actual brace.....

Mick

Exactly

[SilentSteven]

Are you a structural engineer?
 In my experience CB750 is a bit sloppy in handling, removing frame bracing should really 'improve' things 

No where in my post did I say I removed the cross tube. FYI I am a structural engineer 

[Don R]

Touche'

[KeithB]

its mounting tube, the one that transverses the frame below the swing arm.  Its a big chunky hunk of metal

Seems pretty clear to me what part he is talking about. Although, it has nothing to do with mounting the stand, it does provide a place for the stand to rest against when it is down. I don't think it was put there just for that purpose.

You can cut off the tabs but I found them handy as  it's quite easy to slip the stand back in place when I wanted to work on the bike , off the side stand.

[KingCustomCycles.com]

Opinions and more opinions, I got one of those............  "An answer, in case anyone is wondering, would look something like; The Honda frame was designed with a 14% modulus of potential twist about the longitudinal axis.  The tube in question adds 4% to the total of that.  Removal of the tube will adversely effect frame rigidity but not to a degree that is outside of expected failure modes." 

I leave that tube in when I hardtail my frames, I use it to anchor my battery tray. 

[Kong]

Opinions and more opinions, I got one of those............  "An answer, in case anyone is wondering, would look something like; The Honda frame was designed with a 14% modulus of potential twist about the longitudinal axis.  The tube in question adds 4% to the total of that.  Removal of the tube will adversely effect frame rigidity but not to a degree that is outside of expected failure modes." 

I leave that tube in when I hardtail my frames, I use it to anchor my battery tray. 

Thank you very much.  I understand that your "answer" is simply an example, but probably close.  As I survey that part of the frame it occurs to me that the engine mounting scheme (the two rear cross bolts) causes it to be the source of rigidity for the entire swing arm area.  I don't think that tube does much of anything for the frame other than maintain the spacing between the lower lateral tubes, (something also roughly accomplished by the engine mounts) which is intimately related to the swing arm mounting.  So I thought if I did cut it out I'd first weld in a much smaller (1/2" square tube) cross brace to hold the spacing constant.  Basically it looked to me like a place where I could cut out a 3 pound tube and replace it with a 0.3 pound tube.

[Really?]

Me no likee flexy frames!!!!  My Venture had frame flex, SCARY, in high speed corners giving me a warble (hinge-like feeling in the center of the bike).  Changed all 6 mounts from rubber to solid (A job not for the faint of heart).  Tightened that old gal up like a fresh virgin.

[BobbyR]

The heaviest part on the bike is usually the rider. Most of us could probably lose a few pounds and leave frame members alone. Without looking at the Honda data no one has a definitive answer. I work in Engineering for a Japanese Company, they are quite clever about multipurposing parts.

[crazypj]

Nowhere in my post did I say I removed the cross tube. FYI I am a structural engineer  

 That's good to know.
 I miss-read your post. I'll hit you up when I need some work done

[KingCustomCycles.com]

After my earlier response, it occured to me that none of the aftermarket frames back in the day had those tubes.  I am with you Kong, Honda later went to basically a frameless design and used the engine as a load bearing part.  Much like any modern sportbike.  I believe that is what Amen, Santee, and Paughco decided also.  The engine mounts provide the rigidity and the tube is heavy to support the weight of the bike on the centerstand and little else.

[Retro Rocket]

After my earlier response, it occured to me that none of the aftermarket frames back in the day had those tubes.  I am with you Kong, Honda later went to basically a frameless design and used the engine as a load bearing part.  Much like any modern sportbike.  I believe that is what Amen, Santee, and Paughco decided also.  The engine mounts provide the rigidity and the tube is heavy to support the weight of the bike on the centerstand and little else.

Where do these people come from !!!!!!!!!!!!  The old Honda frames are made from tubing with less integrity than modern frames and modern frames are built differently, as we have learned a great deal about frame geometry and performance since then. Anyone that is silly enough to take advice from someone that ruins Honda frames by cutting the back end off and turns them into bodgie rigid piles of #$%* doesn't even come close to qualifying to comment on something he has absolutely no idea about. It is simple to come to that conclusion if you know anything at all about frame technology and the reasons for improvements to modern design. That brace is just in front of one of the weakest parts of the Honda frame, the swingarm pivot, so by removing it you are altering {for the worse} the structural rigidity of the frame and there wasn't much of that to begin with. LEAVE THE CROSS BRACE THERE....it wasn't added just for the stand, its part of the overall frame..... On my bikes , this is one area that i reinforce so my bikes handle better, as well as many other spots....

Mick

[mlinder]

Theres' a reason that another tube is welded to the frame just above that on the go-fast bikes made from these frames...

[Retro Rocket]

Theres' a reason that another tube is welded to the frame just above that on the go-fast bikes made from these frames...

Absolutely....

Mick

[BobbyR]

I am not sure our motors were designed to be load bearing. They may augment the frame in bearing the load. I am sure when Honda went frameless studies were done and the cases were redesigned accordingly.

[Roach]

I agree with BobbyR the cases are not the strongest castings that where made in the earlier models