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Author Topic: 1981 CB750K Project Superleggera  (Read 5386 times)

Offline omgwtfbbq!

  • Posts: 69
Re: 1981 CB750K Project Superleggera
« Reply #60 on: Nov 12, 2016, 14:58:04 »
I am in for this! Very exciting! Supreme work thus far, bbq

Supercool and great work envious of this build love the modern add on's ime in to the finish keep up the good work bud

Thanks guys! I hope to get her running again by the end of the year, then start in on the cosmetic mods (carbon and all that).

Offline omgwtfbbq!

  • Posts: 69
Re: 1981 CB750K Project Superleggera
« Reply #61 on: Nov 15, 2016, 15:56:52 »
Snapped a quick pic of the clearance test. Definitely recommend you engage your safety squints when doing this with harbor freight ratchet straps.


Good news is the wheel cleared everything just fine. Don't know what setups guys are running where clearance is a problem, I could run a straight hoop and not hit the tire.

Offline coyote13

  • Posts: 1057
Re: 1981 CB750K Project Superleggera
« Reply #62 on: Nov 15, 2016, 16:06:01 »
Most guys (who don't know better) run a hoop straight off the line of the seat frame rail and end it right over the top of the tire.  If you draw that straight line in your picture it would be touching not just the tire but the RIM.  Yours looks like it would clear with a hoop because your rear frame rails kick up instead of continuing on a straight line.
Half the fun's in the get there...

Offline omgwtfbbq!

  • Posts: 69
Re: 1981 CB750K Project Superleggera
« Reply #63 on: Nov 15, 2016, 18:13:42 »
Yours looks like it would clear with a hoop because your rear frame rails kick up instead of continuing on a straight line.

Right, I forgot the older bikes don't have the kickup in the frame that the DOHC bikes have. That makes a lot of sense.

Offline bikeWillem

  • Posts: 22
  • Suzuki FTW
Re: 1981 CB750K Project Superleggera
« Reply #64 on: Dec 08, 2016, 09:37:07 »
Nice bike, I like the modern vision of a light caferacer. Mine has a USD fork as well  :D

Offline omgwtfbbq!

  • Posts: 69
Re: 1981 CB750K Project Superleggera
« Reply #65 on: Dec 14, 2016, 03:37:52 »
Little more progress today, cut the excess bits off my upper triple and drilled/tapped the hole to mount my new gauges.

At the start with some of the implements of destruction. I plan on running RFID ignition so I don't need all the bits for the OE ignition cylinder anymore. Yay weight reduction.


Big chunks cut off with the cutoff disc, now onto the grinding wheel for the meat of whats left.


Got a bit tired of grinding and decided to drill and tap the hole for the gauge mount. Finally found a 17/64s bit and tapped it M8x1.25.


And then got back to smoothing things out with the air sander. 50 grit to get the last the grinder left, and a scotch brite pad to smooth everything off.


The only thing left now was to toss it on the bike and see how it looked. I'm very happy with the placement of the gauges and now all I need for this is some more appropriate hardware.



The last major piece I'm missing now is the hoop. Does anyone make premade hoops for the DOHCs? I can't seem to find one that is the right size (7.75" diameter) and my pipe bender only goes down to 9". Once I get a hoop welded on she'll be going back together finally.
« Last Edit: Dec 14, 2016, 03:45:14 by omgwtfbbq! »

Offline omgwtfbbq!

  • Posts: 69
Re: 1981 CB750K Project Superleggera
« Reply #66 on: Dec 29, 2016, 12:09:59 »
Little more progress. Finally got a rear hoop, cut it down, welded it on, refinished the frame and painted the swingarm to match. Today the goal is reassembly!

Test fit after cutting the hoop down


Staring deep into the pretty blue light


Didn't blow any holes in it!


After the final round of paint



Offline CrabsAndCylinders

  • Site Supporter
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  • Posts: 994
  • Careful With That Axe Eugene
Re: 1981 CB750K Project Superleggera
« Reply #67 on: Dec 29, 2016, 14:21:49 »
I usually prefer aluminium swing arms polished up but this one looks great all black and glossy.

Lighter, Quicker, Faster.
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Offline omgwtfbbq!

  • Posts: 69
Re: 1981 CB750K Project Superleggera
« Reply #68 on: Dec 29, 2016, 23:37:44 »
I usually prefer aluminium swing arms polished up but this one looks great all black and glossy.

Yeah I like the polished look usually, but after putting it together I'm glad I went with black too.



Offline omgwtfbbq!

  • Posts: 69
Re: 1981 CB750K Project Superleggera
« Reply #69 on: Jan 08, 2017, 02:46:16 »
A few more minor updates while I await delivery of my new rear sprocket:

Finished my wiring diagram!


What an enormous pain that was, but hopefully it'll save some headache later. I've finally ordered all the connectors I need to build a new harness so the bike might actually run again soon.

On my breaks from doing wiring diagrams I stripped and sprayed my tank:


The tank is temporary, but I figured I'd mess with it anyway because I'm not looking forward to the work I'm probably gonna have to do to get a chain on this thing.


Offline omgwtfbbq!

  • Posts: 69
Re: 1981 CB750K Project Superleggera
« Reply #71 on: Jan 08, 2017, 12:53:57 »
Love it. Especially now that it has decent tires and not the all-seasons it came with from the dealership.

Offline omgwtfbbq!

  • Posts: 69
Re: 1981 CB750K Project Superleggera
« Reply #72 on: Jan 11, 2017, 14:37:49 »
Rear sprocket came in!


This thing is a featherweight. Full 7075-T6 47 tooth 520 sprocket, not the fanciest one they sell but with the high wear rate I'm not willing to spend $80+ every time I need a new one.


Dreading the work ahead I decided to buy a front sprocket on the assumption I'd need to machine it anyway. My local race shop had one in stock for an '04-'12 CBR1000RR.

If you're unaware, every Honda (post 79 at least) uses the same output shaft spline, so it's trivial to mount any sprocket. I needed about a 530-sprocket width offset to get the front in line with the new rear, and since I was able to find no offset sprockets for the DOHC CB750 I had resigned myself to having to fabricate something.

Welllllllll I popped the CBR sprocket out and noticed that it was offset rather far to the inner side. But since sprockets are round they work the same backwards, so I flipped it around and popped my chain on to see how much more I needed to push it out.

Bam! Super super happy with the fitment, super glad I don't have to turn the teeth off the stock sprocket to make it into a spacer.  8)

With that sorted I broke the chain to length and almost made an expensive mistake when I broke it a link shorter than intended.


Luckily it still falls within the adjustment range of the swingarm and I don't have to run two master links like a buddy of mine who bought a bigger rear sprocket and broke his new chain to match the old length  ;D

So now all that's left is to get my carbs back from my buddy who needed a set to get her bike running for an event a couple months back, then a quick harness build once my connectors come in.

Friday I plan on laying up a carbon fiber electric tray/fender for the rear to hold everything that will be hiding under the seat so look for pics of that process this weekend!

Offline Cookie

  • Posts: 380
  • God help the child who grows out of everything
Re: 1981 CB750K Project Superleggera
« Reply #73 on: Jan 11, 2017, 14:54:43 »
That's awesome, bbq looking good!
"I fear the day that technology will surpass our human interaction. The world will have a generation of IDIOTS."

Offline johnu

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Re: 1981 CB750K Project Superleggera
« Reply #74 on: Jan 11, 2017, 16:31:18 »
You got lucky with that sprocket for sure :)  I had to do what you were planing and turn the teeth off of an old sprocket then weld a new one to that to get the offset on my T500.  Bike is looking good :)