Project CB690 (KTM 690 engine in a CB550f frame)

[CrabsAndCylinders]

I like it!

Just for curiosity sake though, why use the flexy old cb frame? Why not swap the swinger and modify the ktm frame for the look you're after?

Granted I'm not familiar with the frame layout, but if it were me I'd probably keep the ktm frame and lop off the subframe and rebuild as a twin shock if that's the look you're after

I was wondering the same thing.

[goodoltup]

A proposed solution for the headstock is shown below. There is not a lot of room in the Z direction to allow for bearing cups, so some compromises may have to be made. In the second two pictures the CB headstock is shown in brown. The KTM bearing is shown in black. The bottom bearing cup is relatively straight forward, it locates in the original CB bearing diameter and would be welded in place. The top cup is more troublesome. There is not enough room to make a diameter that centers in the CB cup, so it locates on the outside. A spacer, shown in blue, sits in the original CB cup and provides a bottom surface for the KTM bearing, shown in black, to sit on. Like the bottom cup, the top cup would be welded in place.

[john83]

Very cool stuff!

[goodoltup]

Did some more mocking up of motor in the frame. Some compromises had to be made to make everything work. I didn't want to cut the frame rail, but the alternator cover is just too low. It would push the injector right up into the frame, and the right hand side of the engine would look like it was floating way above the frame rail. So, I cut the frame rail so the motor can sit down in the frame. Something will have to be devised to reconnect that frame rail, I might make a new frame member with a bender to clear the alternator.
The injector just about clears the frame. I will have to machine a new fuel inlet, the original one was removed for the second photo. The original fuel inlet was just too tall.
The new swingarm plates will locate the pivot 70mm forward, and 12mm down. I have mocked up the plates in cardboard, and tomorrow I will CAD them up and start sending out requests for quotation. I would like to get them laser cut if possible, thickness of plate to be determined. 10mm maybe? Too much?

[Pete12]

Have you thought about bolting your new mounting plates to the inside of the existing plates? It is would make installation and alignment very easy. Apologies if this is what you always intended.

[goodoltup]

^^ Hi Pete,
You are right, it would be easier and more efficient to make plates that fit on the inside, or the outside, of the original mounts. But I would be concerned about any movement allowed by the bolt-plate interfaces, I think a weld would be more secure. I guess you could weld the plate to the original mounts, but all in all, I think it would be more attractive to make new mounts and have them welded in.

[Pete12]

^^ Hi Pete,
You are right, it would be easier and more efficient to make plates that fit on the inside, or the outside, of the original mounts. But I would be concerned about any movement allowed by the bolt-plate interfaces, I think a weld would be more secure. I guess you could weld the plate to the original mounts, but all in all, I think it would be more attractive to make new mounts and have them welded in.

Very true, it would look a lot more professional making the whole new mounting. Great project, by the way, looking forward to seeing the end result.

[goodoltup]

Moving ahead slowly. I got quotes from tube benders for the frame member that will be welded in place to clear the alternator cover. I also got quotes on laser-cut and water-jet swingarm and engine mount plates. All very reasonable.

[XS750AU]

Hi, if you don't mind sharing. What do you consider as reasonable?

Sent from my SM-G900I using DO THE TON mobile app

[hooligan998]

Very interesting project.  I'm in.