CB750k Street Tracker

I know, you are probably thinking WTF dude, finish your other 3 builds.

Well, there's an answer for that, and it starts like this.

"Hi, my name is Peter, and I have a bike problem..."

The Ninja is barely out of the gate with 200 miles on the build and I'm starting another project. This one has been in the works for awhile. Ever since I saw this pic, I was in love. It's a tribute to the Bubba Shobert RS750





I will be departing from the standard tracker a bit.

As I have yet to buy a part this is all subject to extreme revision

Front end-Aprilia RSVR Mille forks, radial Brembo brakes
Front Wheel-KZ1000 wire spoke wheel. Custom carriers for discs. 1.85"x19 rim
Tank-Airtech Streamlining RS750 tank
Seat-Airtech Streamlining RS750 seat
Tail-Airtech Streamlining RS750 tail
Swingarm-CBR600F4i swingarm
Rear wheel-KZ1000 with custom carrier (not sure this is going to work, might need to go $$$ and get a A&A racing knockoff hub)
Rear suspension-CBR600F4i shock and linkage

So I will be monoshocking this bike and I am excited to do it. Part of me wants to go traditional as I have a hawt set of Paioli piggyback shocks I have been dying to use. But I like to screw around. Same for the front. I toyed around with not using a front brake then decided that 640mm of stopping power was really what I wanted.

I plan to eliminate the oil tank from it's current location and see where else it can go. I've seen some creative places for it under the seat, sideways in the frame, under the motor like the RS750 had. I like that back triangle open course the DOHC motors had no oil tank...



I will probably have to get custom triples made, although this will depend on how the front end feels. I would like to keep this a reasonable build and not some super high bling, money no object type build. I am using the Aprilia front end as a local riding buddy had it over at his house last week when I went to help him move a gun safe. I had the CB750 in the truck, conveniently, as I had just gone to pick it up. Held the forks up next to the bike and said, "Yeah, I can make that work..."

Famous last words.

And here's our lovely lady. 1977 CB750k. Miles unknown, although I have heard it run from the seller who started it with no header and a donor gas tank. Runs good. He pried $300 from my hands for this beauty and then another $50 escaped my pocket for a mint 4-1 header (model unknown but looks like a Kook's to my untrained eye)



I plan to start tearing it up and having my usual fun. Expect mistakes to be made, choices you would not have made and everything else involved in a fun project.

Yep, I never figured you staying away from these deep hands on progects.Not that you should. you're honing your skills, figuring the possibilities, and making cool stuff, and keeping the rest of us entertained. Could be worse.

My wife confronted me about my 2 wheeled addiction, said I spent too much time , reading about them , working on them and riding them.

So , I say, "You're right. I'm going to give them a break and find some new hobbies. I'm going with Drinking, Gambleing and Running around with loose women. It'll be great , whole new avenues to explore !

She said, "Just keep your mind on the bikes. "

Yeah I think my wife has finally come to that conclusion as well. She knows where she can find me...

Got the bike stripped down, not that there was a lot on it anyhow...I think I'm going to wait until I have a couple more hands for the engine removal, bastard is heavy. Quick peek at the internals shows a motor in relatively good kit.

I just dragged a rust bucket Edsel home. :huh

It keeps me out of trouble.

Curious to see how you do the mono shock, Sailah. Thinking of doing the same to my 490 powered tracker.

I'm using a CBR600 F3 swingarm as a mockup but plan to go to a F4 swingarm as they are aluminum. The linkage on the CBR is above the swingarm which gives me the raked shock look that I like. Both swingarms are a red c hair away from fitting right in the CB750 frame.

I stripped the frame down and shaved off a bunch of brackets I don't want anymore. Got the mockup swingarm in there, fits with just a slight shave to the bearing spacers, maybe 1mm. I just threw on a CBRf3 shock and linkage. Need to spend time to make sure I get the linkage right as I don't have anyway to measure it since my CBR frame is highly modified.





I'm also considering cutting the red tube and replacing it with the blue tube just to make things interesting, but not sure I will.



I designed out some frame bracing triangles that I was going to cut on the waterjet but then the machine decided it didn't like me so I need to wait a few days let it cool off...

I'm sure the Aprilia RSV 1000 Mille didn't have radial brakes it was only fitted on the 06 onwards RSV1000R?

I do love these older Honda 4 bangers they need to bring back a smaller CB aircooled 4.

If I score another Ninja cheap enough, I was thinking about a tracker build

You are most likely correct, I know it has radial brakes and it's an aprilia might even be a tuono for all I know. I do know the forks are hot with the gold anodized finish though

Check VFT.org for the A/A wheel. They came up fairly often.

Cleaned up the frame and prepped a few things to get ready for the new aluminum CBR swingarm and shock that are inbound.

You are looking at the underside of the top frame rail junction



Cut out a plate that will have the shock mount arms welded to it and to the top diagonal tube





Gussets were added to the frame



The CBR shock is raked really far forward in a stock bike. I'm going to cut some 3/16" plate arms similar to what I did on the Ninja. These arms will be welded to that flat plate above and also tie into the downtube. To keep them from flexing I will add some DOM tube spacers at 29.5mm.

The arms will be gusseted to the vertical tubes with some fancy ass design I whip up and will be braced down below with tubing to the swingarm area. This is all off the top of my head and will be subject to extreme revision based on the scientific calculation that none of that shit will actually fit back there... I need to be careful adding all this stuff without the motor in the frame make sure I can get it in there.

Ordered up the swingarm, shock and scored (2) KZ1000 wire spoke wheels for $30

Built an oil tank to sit in front of the wheel. Not sure I like it. I was trying to keep that triangle open but I'm thinking that might be tough. It's about 3.2 quarts according to CAD. I had to smack the sides in to get it to fit and clear the shock. I might redo this once I get the actual shock and linkage in.

Mocked up the upper shock mount. I made these parts out of scrap, the real parts will be 3/16" plate for the main rails and will join the downtube with their extra width.

I'll have to grind the plate to fit around the tube brazes









I have the new CBR 954 shock mocked up. Only thing left is to secure the lower dogbone. I'll wait on that until I have my aluminum swingarm and the mockup wheels to make sure it's going to be good on ride height. I suspect I'll have to modify the real plates once I get those in place.

I made some progress on the wheel situation. I have some KZ1000 wheels coming but I am going to most likely use Harley Sportster hubs for the front and rear. The rear should be easy to get right by using a sportster hub and brake rotor



The front is going to be slightly harder as the rotors I wanted to use were 320mm and 6 bolt. The is no easy way to machine an adapter from 5 lug to 6 but I remembered a GSXR rotor I have in the parts bin that was a 5 lug. I believe early Hayabusas use 5 lug 320mm rotos and that will be much easier to machine adapters for. So I think that is the direction I will go.



Any and all comments and concerns welcomed.

Cool build, I'm in.

designed the rotor spacer for the Hayabusa rotors to the Harley hub. Inventor moves between inches and mm so easily, made this in about 2 minutes and same amount of time on the WJ I'll have a aluminum adapter. I suspect I'll need to use the lathe to get the thickness I need for the rotors to line up with the Aprilia/Brembo radial calipers. I want to leave the front Aprilia fork setup stock becuase I also have a Shiver 750 wheel that I can bolt on if I want to go with a set of sticky tires.

Got the dogbone mount done. Had a major brain malfunction and made a previous version that essentially had the dogbone in a straight line, hard to explain but it bound up the entire linkage. I went to cycle the swingarm and nuthin'. Took me a second to realize what I did so it meant I needed to move the mount point much further away from the frame crossmember. I wasn't happy about the mount just attached to the one crossmember especially with the forces applied by that link in tension so I ran another crossmember on the bottom of the frame.

The frame mounts I designed up and cut on the waterjet. I will be making them from heavier plate once I verify that I get the correct sag. With the swingarm about as "neutral" as I can guess, I have 305mm between shock mounts. The CBR954 shock is 295. So I will most likely redesign the top mount I showed above and drop it down and back to make up the 10mm. I suspect I will have to further refine the mounts and sag once I get the front end mocked up to ensure the rake on the forks is correct.





The Duro 4.00 19" tire I plan to use is 27.4" OD which is almost exactly what a front 21" dirt tire is. So this is pretty darn close to what it will look like but the 19" will have more sidewall.

Decided to redo the oil tank as I did not like the chunky version I made earlier.

I cut out the crossmember between the frame rails. This mockup is 0.080" steel as that what was laying on the waterjet. I plan to do the real version from aluminum.



Here's about what it will look like. The thin end is 1" inside dimension and I get 3.25 quarts



Top will be drilled and tapped into the frame rails

I'm not sure what happened to me today but I think I made a serious mistake:eek1

I got my sweet swingarm in the mail and measured the width. 10.25"

The width of the opening...9.25"


Scroll down only if you aren't squeamish...











































I set up the frame in the mill to bore the mounts to 30mm. It was a pretty exciting cut as the frame doesn't have a lot of rigidity





Then I rough sectioned out the frame with a cutoff wheel



The plan is to plate the inside using the 30mm bores on the outside as an index and the swingarm bolt holding everything in line. I will then plate the outside with a much larger plate to help tie in various motor mounts etc. It was a bitch to draw this frame plate and many revisions.



I'm seriously considering doing the back end of the bike from scratch at this point. It's a lot of work to fit things to the hacked up frame and if I was free to redo it, I think I can draw things out and weld them up straight without having to deal with what is there. Your thoughts?

My thoughts....I wish I had your work space and tools.

^^haha yeah it's pretty nice.

I resumed on the frame mods. Spent all day grinding and mostly filing away to get the 10.25" clearance I needed for the swingarm. It was a LONG day. Made some pivot bosses as well.

Haven't welded anything yet just got things lined up





The wheel is the right diameter but not the wheel I'll be using. The bike is sitting a bit low right now, esp with no sag. I'll wait to change the mounts until I get the forks mounted to ensure I don't box myself in with the rake angle.



Got my sportster hub in (first Harley part I have ever bought...) Why the hell do they use tapered roller bearings? I had to weld a fat bead on the inner races to get them to drop out. I made up an adapter to bolt the hub to so I can chuck it in the lathe. The plan is to machine out the hub for 47mm OD bearings that way I can press in some metric bearings with a 25mm ID for the Aprilia axle. The hub has about a 45mm bore right now. It also seriously heavy. I'll need to weld it and then face it again. Fun project. I used the same CAD file for the rotor adapters from the Sportster hub to 320mm Suzuki rotors.

Coool