Topic: CB750 project - is this subframe good?

[macvit7906]

Honest opinions and criticism is welcome!

I'll start off this build thread with the sub frame I've been working on. Over the course of the past year I've been learning how to weld (MIG), notch and bend tubes, etc.

The sub frame is almost done with the exception of the shock mounts.
I've highlighted where I put gussets for added strength.

The tubing used is cold rolled DOM steel tube with 0.12" thick wall and the gussets are either 1/4" of 3/8" thick steel

How does it look?!
More importantly, will it be strong enough? I'm pretty confident in my welds.
Any other recommended gusseting?

[macvit7906]

Has anyone here modified their sub-frame?

[macvit7906]

That is massively stronger than stock. Stock wall thickness is 0.063. Yes, I've modified many subframes, even made bolt-on aluminum ones.

The only thing you need to absolutely confirm is shock travel to the seat section. Remove the rear shock spring, compress shock completely to check for interference/contact. If none, you're good (reassemble shock). If conflict, resolve it.

Great thanks. I guess I went a little crazy with gussets.

I do not have shocks yet. Im about to order a set of YSS shocks, ordering a length based on 3 1/2" of clearance between tire and seat section. That good? 

[macvit7906]

I have no way to make that determination. What size tire? What length overall on the shock? Where is rider's weight relative to the shock? Has the shock angle changed from stock? Etc., etc.

Best you can do is install it when you get without the spring, run the test I described, then "spring" it based upon the results.

All good. YSS helped me determine the travel without springs is 3.4" - so that's how much clearance I need

[754]

Well sort of, alway best to check with springs off the shocks.
 You over built, heavy, not always better, thicker gussets tend to promote cracking as  vibrations concentrate at them, rather than pass thru....so far as I have learned..

[macvit7906]

Well sort of, alway best to check with springs off the shocks.
 You over built, heavy, not always better, thicker Gus sets tend to promote cracking as  vibrations concentrate at them, rather than pass thru....so far as I have learned..

Makes sense. Too late now 

The large gussets are all 1/4" thick. I figured since I moved the down tube from the shock mounts to such an increased angle, it could use the extra strength. I'll be sure to keep my eye on the gussets after im riding. Thanks!

[754]

It likely wont break, just pointing out bigger is not always better.. but it is heavier.