Author Topic: 1977 CB750K undergoes full reconstructive surgery (Read 6320 times)

sailah · « **on:** July 17, 2013, 06:51:01 PM »

Hey SOHC forum, n00b here. Thought you might enjoy my latest frankenbike build.

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 forks, radial Brembo brakes from an Aprilia Shiver 750
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-CBR954 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 thinking of 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.

I will be rebuilding the engine but I don't know what shape it's in. I'll do a compression test, hopefully I can get away with the basics.

sailah · « **Reply #1 on:** July 17, 2013, 07:06:27 PM »

Couple of my other projects in various stages of testing...

Ninja 650. KTM 450 EXC front end, EMIG billet triples with damper, KTM 450 swingarm and PDS shock. Fuel system is completely revamped, main tank welded, aluminum subtank mounted under the seat which houses fuel pump. A real riot. Just got this on the road and need the summer of testing before I tear it down for finish work. Also plan a rally fairing for this, have the parts just got distracted...

FZ1, my original frankenbike. KTM 950 front end, back end including wheels, Brembos etc. Ivans Pod filter setup, 140 HP. Gets ahead of itself with a 21" front end. I've put 25k on this bike in the last 2.5 years and it's run great. I would do a lot of things differently if I knew what I knew now. Maybe I will redo things esp the seating, not the most comfortable bike out there but I have done 2000 miles in 4 days a few times.

CBR600F3. I sorta scrapped this bike when I went to the Ninja. It was a little too violent

105HP and 360 lbs fully fueled. I still have a full sumo setup on it, which is a little ridiculous when you think about the efforts to go full circle to put sport bike tires back on it..no one ever accused me of being smart...

Anyways all my builds are on another site if you want to check them out, just thought I would post them up if anyone thought I was crazy enough to actually attempt all this stupid stuff haha

sailah · « **Reply #2 on:** July 17, 2013, 07:12:49 PM »

back to the SOHC...

I got the bike torn down which took almost no time. Blessedly simple and I like that.

I'm using a CBR600 F3 swingarm as a mockup but plan to go to a F4i 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 have a CBR 954 shock on the way from eBay as well as a mint swingarm.

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...

sailah · « **Reply #3 on:** July 17, 2013, 07:17:20 PM »

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 stuff will actually fit back there... I need to be careful adding all this without the motor in the frame make sure I can get it in there.

sailah · « **Reply #4 on:** July 17, 2013, 07:18:18 PM »

Scored (2) KZ1000 wire spoke wheels for $30:D

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.

sailah · « **Reply #5 on:** July 20, 2013, 07:20:34 PM »

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.

sander · « **Reply #6 on:** July 21, 2013, 03:03:38 AM »

Impressive.. You have done some crazy projects! Great fabricating skills by the way, the shock mount looks very well thought out. I'm really looking forward to see the end result!

sailah · « **Reply #7 on:** July 21, 2013, 06:09:43 AM »

Quote from: sander on July 21, 2013, 03:03:38 AM

Impressive.. You have done some crazy projects! Great fabricating skills by the way, the shock mount looks very well thought out. I'm really looking forward to see the end result!

Thanks for the kind words regarding fabricating skills, the FZ1 project was the first time I ever even saw a TIG welder. Taught myself just by doing, and redoing, and redoing and grinding and redoing...haha I very much enjoy the fabricating I wish I did it for a day job.

Since the FZ1 I have acquired a 14x40 lathe, a Lincoln TIG welder (previous was a chicom inverter machine that was actually pretty decent) and loads of tools and tooling. Probably the biggest help has been to have access to a shop that has a waterjet and CAD stations.

For example last night around 9, I started that shock mount. Took my calipers, Sharpie and cardboard over to the bike and started sketching. Threw down my measurements in AutoCad Inventor and five minutes later (actually 15 after I cleared the clog in the waterjet nozzle...) I had the test part in my hand. I knew some dimensions weren't right so I modified the drawing and about 20 minutes later had the main brackets you see. I'll probably revise them again. The side braces were easy, measure, draw, hit GO on the waterjet. I was done with that bracket it 2 hours and it's true to measurements. no way I could do that nice of a job by hand, no way.

There is a lot you can do with basic hand tools, but having access to really pro fab tools and the knowledge to get the best out of said tools, helps. I'm still a beginner using these types of machines, but I try to learn quickly.

BTW, I'm building this at a Tech Shop, if there is one in your area, you should check them out. For the membership costs, you get access to a LOT of tools. Powdercoating booth (6x6x6), waterjet, mills (manual and CNC), lathes, welders, sandblast, ironworker, shear, slip roll, english wheel, planishing hammer, laser, CAD, sewing etc.

sailah · « **Reply #8 on:** July 21, 2013, 06:35:39 AM »

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.

sander · « **Reply #9 on:** July 22, 2013, 02:56:21 AM »

Oke that surprises me, you are talented then! Having access to the right tools definitely helps. I use Inventor all the time at work, it saves me a lot of time when designing constructions.

I have never heard of the Tech Shop concept over here but it sounds promising!

sailah · « **Reply #10 on:** July 22, 2013, 12:30:17 PM »

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.

sailah · « **Reply #11 on:** July 22, 2013, 02:58:25 PM »

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

Had a minor setback today. The KZ1000 wheels came in and the rims are MINT. Beautiful DID 1.85 x 19" shouldered rims. I'm thinking to myself that's a lot of spokes. 48 to be exact. My new Harley hubs are 40...grrrr. Will keep shopping for rims. Might just spring for some from Buchanons.

Ordered the tank, seatpan and numberplate from Airtech today. 5 week leadtime.

sailah · « **Reply #12 on:** July 22, 2013, 04:51:33 PM »

I'm running myself silly trying to figure out rims and sizes.

I am going wire spoke and would like to use shouldered rims.

I think 19" is the preferred rim size F&R correct?

Here's my issue. I bought a pair of 19" KZ1000 wheels with sweet 1.85" DID rims only to find out they were 48 spoke and I need 40.

I'm using a Harley dual disc Sportster hub for the front and same on the rear.

While I want to go 19", couple things pulling me to 18" rims. First tire selection is MUCH better at 18 vs 19. Finding rims in the 19" shouldered variety isn't hard they are just twice as expensive as 18" rims.

Any reason other than authenticity not to go 18? And as far as authentic goes, I'm running a CBR600F4i swingarm, monoshock, flat oil tank under seat, Aprilia USD front forks and 320mm radial brakes so....

Thanks for your suggestions

brandEn · « **Reply #13 on:** July 22, 2013, 05:01:50 PM »

This build is off to the right start!
Subscribed.

sailah · « **Reply #14 on:** July 23, 2013, 04:02:50 PM »

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

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 #$%* 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?

iron_worker · « **Reply #15 on:** July 24, 2013, 06:49:47 AM »

You're really diving into this project and not holding back.

I'm interested!

IW

sander · « **Reply #16 on:** July 24, 2013, 08:17:04 AM »

My swingarm was also an inch too wide, so i just cut the frame and stretched it up.

Bankerdanny · « **Reply #17 on:** July 24, 2013, 09:15:27 AM »

I just Googled Tech Shop, what a great concept. I would LOVE for one to open up in the Chicago area. Sadly the nearest one is in the Detroit area.

Great project.

SF · « **Reply #18 on:** July 24, 2013, 10:33:35 AM »

real cool processes! the end result will be interesting. welldone man!

RAFster122s · « **Reply #19 on:** July 24, 2013, 11:51:12 AM »

Pretty wild bit of work. Outside the box for certain.

Tech Shop would be super to have. In Ontario back in the 90s I used an auto shop open to the public that was quite nice and inexpensive. Had air tools, lifts, fluid disposal, even tools you could check out. With the US litigation and insurance nightmares I don't see it working.

sailah · « **Reply #20 on:** July 24, 2013, 03:12:52 PM »

Thanks guys. I enjoy a challenge and can't seem to leave well enough alone.

The Tech Shop is pretty cool, you really need to see one in action to appreciate the tools you get to use. I've been at the Pittsburgh Tech Shop since it opened. They seem to have done really well esp by encouraging long term membership vs people that want to come in and leave things a mess and abuse the equipment.

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.

Bought a rear Sportster hub so I know what I need to do in the back.

Any suggestions on rims and size? I know 19 is the standard but the tires choices aren't good. 18 is much cheaper, easier to find and tires are much better.

sailah · « **Reply #21 on:** July 24, 2013, 03:15:51 PM »

BTW that swingarm was unused. Totally brand new without a spec of dirt on it. $40 on eBay. Course that was the cheapest part considering the amount of work that went into adapting it. I think it looks great back there though.

SOHC4 Cafe Racer Fan · « **Reply #22 on:** July 24, 2013, 05:18:02 PM »

Piston & Chain in San Francisco is similar to the Tech Shop but limited to people wrenching on their motorcycles -- mostly classics. So many people in the City of SF don't have garage space to work on their rides, so it's a great idea. Plus, the club organizes abundant events including clinics to tech amateurs how to do specific tasks. Nice people, too! I don't live in SF, but I happened upon Piston & Chain during a visit about a half a year ago.

http://www.pistonandchain.com/

sailah · « **Reply #23 on:** July 24, 2013, 05:45:13 PM »

That Piston & Chain is pretty cool. I think Tech Shop is about $100/month. But you get access to WAY more tools. Having a $250k waterjet just waiting for me to use it? Yes please. Full AutoDesk licenses for everything they make. There are $20k worth of licenses on each of the 50 workstations they have here. It's not really geared towards bikes but believe me, there are plenty of bikers here. Just think what a powdercoat job costs on a bike and it's not that hard. They have an oven so big here you could fit 2-3 frames in at once. And a paint booth...

At $100/month there is no way you could afford to buy all the stationary tools they have. I do bring all my own endmills, drill bits, carbides, calipers etc. I basically use their machines but all my own tooling.

Anyways, check out a Tech Shop if they have one close by to you they are rad.

Long day of grinding and filing but I finally got the swingarm installed. It needs some tweaking though. I also plan to plate the outside of the frame to help stiffen it up and will look into bracing down to the crossmember too.

I will probably take a break from the bike for a week I am headed up to Maine for some business so don't get nervous that I bailed on you hehe. I'm also waiting on my buddy with the forks to get back from dirt biking so I want those in hand before I go any further with the rear suspension.

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Author Topic: 1977 CB750K undergoes full reconstructive surgery (Read 6320 times)