Topic: CB750 First Build

[calj737]

Simple - yep, the factory tubing is pretty darn thin. It's like 0.016 wall thickness. Good news is that you probably haven't destroyed the structural integrity, but it does need to be welded back. Any competent welder can TIG it back or even MIG it back and fill the spot. Having the ability to see the wall thickness will help them avoid using too much heat and burning through during the repair.

Don't fret, metal is easy to fix. Once welded, it will be stronger than when it left the factory.

But; be mindful when de-tabbing the bike. The tubing is thin. Don't bear down too hard with a grinder to make it smooth. Get it close, then use a less coarse pad to smoothe out. Or you will eat through or flatten the tubing.

[754]

.60 -.62 a lot of it..

[Simple]

As of late, I have gotten the frame and swingarm blasted.  I have started to strip the frame of some of the excess metal but have run into an issue.  I screwed up a bit and put a hole in the back side of the frame pipe where one of the passenger "tranglular" set mounts was.  Only after I made the mistake did I realize the thickness of the tubing was so minimal.  I know, this was a newb move and avoidable with some more research.  My question is though how should I go about fixing this?  I will most likely have someone else do the welding as I don't have the proper equipment nor trust my welding skill.  Maybe I can get some pics to give you a better idea.  Thanks for any comments, I'm at a little bit of a stand still...

When you say triangular are you talking about the gusset plates? How big is the hole? Pix would be great if you have any. I know now that the frame is supposed to have some breather holes by the gusset plates and then at the lowest points by the engine mount brackets on the down tube (see page 4 of my build thread for details). I may be completely off here, but if you were only grinding, you may have just unclogged one of the holes. Hard to tell (for me) without the pix though...

No, I'm talking about the "passenger peg" brackets or mounts.  After I cut them off I was grinding those spots clean.  My mistake was that I used a side grinder instead of a disc sander to get the frame metal smooth again.    I will try and get a picture yet for a better idea but I haven't been to my shop in a while.

[Simple]

Simple - yep, the factory tubing is pretty darn thin. It's like 0.016 wall thickness. Good news is that you probably haven't destroyed the structural integrity, but it does need to be welded back. Any competent welder can TIG it back or even MIG it back and fill the spot. Having the ability to see the wall thickness will help them avoid using too much heat and burning through during the repair.

Don't fret, metal is easy to fix. Once welded, it will be stronger than when it left the factory.

But; be mindful when de-tabbing the bike. The tubing is thin. Don't bear down too hard with a grinder to make it smooth. Get it close, then use a less coarse pad to smoothe out. Or you will eat through or flatten the tubing.

I am sure I am not the first one to do this...  Unfortunately I had to learn this lesson the hard way.  Do you think that just filling in the hole with weld will suffice?  I thought maybe I should have this part cut out and replaced with a new piece...  I want to do it right though and have it just as strong as before if possible.  Standby for pictures.

[Simple]

I got to ask..
 Is the red bike in the background, an old carnival piece? Or maybe a Ridley?

The little pocket bike?? I'm not sure, not mine.  It was supposed to get a weed trimmer motor transplant or something but the project was never finished, haha.

[calj737]

If the hole is not that large, then it can be filled. Probably need a pico give a valid opinion.

[Simple]

Here are those pics regarding the frame mishaps.  Any input from the fabrication pros would be well appreciated on how I should go about fixing this.  obviously I want the frame to be strong for my build and want to get this fixed the right way, thanks guys...

[Simple]

Also something to note, when I was taking off the rear peg brackets using the side grinder, where I was grinding has a wavy feel along the pipe  .  My thought is to maybe just have the whole sections cut and replaced...

I don't know though.

[calj737]

Other than the hole, I don't see other damage. The welds above (shock gusset) and below look in tact. That brace is really important if you are riding 2-up. From the picture, it can be filled and ground smooth again.

If you can't weld it, then whomever does can double-check the rest of the frame for other damage. But that area is not a place likely to rust. Generally occurs at the bottom where moisture can be trapped and sits, or the frame sits in contact with the ground for extended periods while abandoned.

[minenone]

Hi, what happened to that 16" rear wheel of yours? I'm looking for one for my '74 CB750.

Best, Mika