Noob mistake

Alright guys. Here's the short of it. I cut the rear subframe out of my 80 CB750 F. In the process of cutting the old factory wrapped 1 inch horizontal tubing loose, I sliced into the 1 1/4 rear down tube with the grinder on both sides. The cuts are each about 2 inches long and the frame is otherwise in great condition. My question is can I weld the seams shut or do I have to buy another frame? The cuts are near a bend so sleeving the inside doesn't seem to be an option. The is about the point where the new horizontal rear subframe bars will tie in and they will be gusseted. I also considered running a piece of 1 inch tubing between the affected areas but I am afraid to much rigidity may cause more harm than good.

In case you're wondering why I didn't just hoop the rear end, I've switched to a Hondamatic tank. This tank mounts with a slight upward angle and created a slight peak from the back of the tank to the back of the frame. I also want to create a bit of rake and get the frame up off the tire just a bit more.

I would weld that up. In a second. But that's me.

Don't know how good you are with a welder. So your results might vary...


Too much rigidity, in a 70's steel cradle frame. LOL.

That was the plan jcw. I've got the old subframe for a test mule so the plan was to try it on a section there and then do some destructive testing and grind it out to check penetration. I think I'll stick with that plan. Thanks for the input!

Practice, practice, practice.

This can be welded, but I'm thinking that you likely don't have the experience (yet) to do a proper and safe job of it because if you did, you would have known not to have got into this situation. Structural chassis welding on a bike frame needs a trained hand, so have a pro help you out until you get there yourself. For future alterations, try a lot less grinding and a lot more filing. That's right with hand files. That is what the most skilled folks do. Hand filing is very fast and extremely precise - sort of exactly like an angle grinder isn't - even in experienced hands. Here is an example: These were holes butchered into the frame by a previous owner and welded up. This took maybe a little more than 5 minutes of hand work. Absolutely flawless results very easily obtained, and an average person will develop the skill very quickly as it is very intuitive. And since you remove material relatively slowly mistakes are few. As a rule, I remove major items with a saws-all or hand hack saw, then grind fairly close with an angle grinder, and finish up with hand files. These welds only needed hand filing. You can see how this looked after painting in the build thread at the bottom.

As much as it hurts my pride Mobius you are correct. In fact, for the subframe assembly I was going to cut, notch, fit and tack everything into place and leave final welding to a friend who is capable. Now he just has a bit more to do. (Good thing beer is cheap lol)

I was more worried about structural integrity in the long term in regard to the tubing itself. However, from what I've read Dom is pretty receptive to mig welding.

Ill remember what you said about hand filing. Thanks for the guidance.