How-to | CB750 Rear Frame Loop

Stripping an old bike down to its bare bones looks awesome but can often look unfinished unless few simple modifications are done to complete the look. Of these, fabricating a rear loop is the easiest way to clean up the rear of the bike. It also stiffens it and gives some more options for mounting the fender, tail light, and license plate.

This is a 1979 CB750 frame that came to our shop with the rear already chopped off and needing the rear loop fabricated. Here’s the steps to make that happen:

1. Clean up the frame and remove the extra metal that was used for bulking up the oem pinched frame ends using a chisel and folding it in on itself until it falls out.

2. Measure the inside diameter (ID), outside diameter (OD), and center-to-center width. You’ll need this for the layout of the frame hoop and picking out tubing.

3. Cut 2″ pieces from tubing with the same OD as the ID of the frame. These will be used as slugs between the frame and the new section which helps align and strength the joint. I missed getting a photo of this mocked up in the frame but you get the concept.

4. Using the appropriate die, make a 180 degree bend in the same OD tubing as the frame.

5. Layout out your cuts to fit the frame width and tack it together to check fitment. All butt joints should be beveled to prep for welding.

6. Weld!

7. Clean up the welds using whatever method you prefer. I like to use a flap wheel to do the majority of the work while leaving a small amount proud of the tubing OD to be finished off with hand files in order to get seamless, smooth finish leaving no indication of a joint.

Get in touch with us at Cast & Salvage if you’re looking to get a rear hoop or any other frame modification done on your project bike. We love this stuff.

8 responses to “How-to | CB750 Rear Frame Loop”

  1. Chris f says:

    Ok, now that you posted this we gotta do a swingarm extension, You make it look too easy!

  2. ed says:

    haha. yea…
    make one of those crazy long swing arms, and put it on ricky’s KZ.
    rolling dirty.
    don’t forget the LED lights underneath.

  3. Chris francione says:

    Goddammit Ed I’m serious…you just wait and see. Sans LEDs .

  4. Ben says:

    Yo Chris- I think Alex-the-kid has a nazi helmet with a spike on it, to complete your look.

  5. Adam says:

    Yea, Chris isn’t kidding. We’re extending a swing arm for him in the next few weeks. It’s gonna be sweet

  6. Chris francione says:

    @ben, I’ve already got one… It’s pink!

  7. Jason says:

    What was the diameter of the hoop for the 79 cb750?

  8. Sam says:

    Hey, I have a CB650c with the same annoying downward angle on the frame by the rear shock mounts. Any suggestions for flattening that out, or will you hide it with the seat pan?

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