73 CL 350 frame welding...


I have the frame stripped and it's ready to go the welder soon. My goal is to stiffen the frame to reduce flex. I will have the welder tig up the seams, but I am also interested in adding stiffeners from the rear spine to the down tubes. Does anyone have pics or dimensions handy or point me in the right direction on where to find this info? The frame will not be detabbed or cut. The bike will be staying essentially stock with a few upgrades like 18" hoops front and rear to utilize better rubber, electronic ignition for reliability, upgraded suspension for better handling and a few other mods to strengthen performance and endurance.



Books, Books, Books, knowledge is within
Wow. Stock frame and its not strong enough? REa;ly unless you are racing it with some huge oversized engine, thats a pretty stiff frame already.



Keep er' Between the ditches
Also, be careful welding up the gussets that are already there. The un-welded ends are there by design. The frame will flex some, its made to and those are often left un-welded by design. The frame will still try to flex like before, and those areas are designed for the movement. Welding them may result in cracked welds.


Active Member
Some of the vintage racers carefully grind down the big weld on the backbone and tig up the seam. They both remove and weld in small segments, the sheet metal backbone is thin. I've seen stiffing gussets at the lower edge of the triangle under the battery box. Here's some info on building a WERA Vintage racer http://www.eurospares.com/framemod.htm


Active Member
This is a race bike where I had a very tiny bit of involvement. http://www.sundialmotosports.com/hondacb350.htm


The original plan is to just weld the seams along the parts of the frame that are stamped to increase rigidity. I have ridden this bike up at Deals Gap and the bike tended to wallow in the turns. I know that this is a combination of things and not just the frame, therefore my goal is to have and better handling CL when all is said and done. I had not planned on welding up any of the gussets. As far at stiffeners that run from the rear of the spine to the rear down tubes, it was in an article that I had read some years back about a frame prepared for racing. There are no engine mods planned at this time, nor will there be until the bike is done and dialed in. After that, some engine mods might be considered.

The idea is to keep it all original, even down to the goofy ass tail light, but to make it so it's more fun in the turns.

Most of my experience lies in more modern sportbikes, therefore I'd like to hear more constructive feedback on mods to make the old CL handle as best as it can.

Thanks Hurc and Rider for the feedback.


New Member
Here’s an option, using a 1” square tubing.


The Limey

Evil English Villain
Is it not stiff enough as standard? Unless you're blowing your wad on top flight Online or WP suspension and super sporty tyres, efforts to reduce frame flex are somewhat pointless.


I'm all about pointlessness. And it was free. Well, a case of beer. But I helped empty the case, so there's that. But the plan is to fit up a quality suspension to it.


Old thread revitalization.

I have a 350 and I’m about to do the same. These guys are nuts that some flexibility is designed in. They are flexible because it’s made of stamped steel and mass produced. My kz1000 would have so much “designed in” flexibility it’s a death trap. It’s called death wobble and no engineer added it.

Stiffen it. No one likes a limp noodle.


Yea, I've had this thing on the Dragon and I know how flimsy it is. Hence the reason I welded the seams. This is a long term project as I've got other brands in the fire to attend to, but one day this thing will be eating sport bikes in the curves even better than it did before. It's going to be original old school looks with modern/updated suspension, wheels, tires and electrical/electronics.


I went with a 71 CB500 front end on mine... staid with factory wheel sizes for now though.

I just finished assembling the engine so next will be some frame welding. Maybe see you up there one day I ride out of Maryville TN some times.


That would be cool. I'll actually be up there first weekend in June with my FZ for a rally. In fact, I'm getting a valve clearance check out of the way and some other maintenance done now while the weather is shit.


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