Author Topic: '81 CB750KZ Brat  (Read 5894 times)

Offline xb33bsa

  • Posts: 7726
Re: '81 CB750KZ Brat
« Reply #10 on: Dec 18, 2015, 22:53:38 »
great diagram and as you can see look at the top one a stright line is between the 3 axis this is what determines how much chain slack you must have and is what the oem spec goes by
because as the wheel travels above or belo this straight line the chain becomes looser because the rear axle is getting closer to the cs sprocket
so if the stock spec is say 1-1/4" slack while on the centerstand this is because when the wheel comes up to the 3 axis staright line it will be near dead tight
dropping the swingarm creates more slack that cannot be adjusted out because you will break something i hope this was a good splainin
dropping the swingarm only 1" could easily create an extra 1-1/2" slack that you cannot do anything about
except a roller tensioner
this all is a very easy thing to actually observe put the bike up on centerstand unhook shocks and move swingarm thru travel
all new motorcycles (evenj street bikes )ever since the early 80's or so have had a gearbox re-design to put the c/s sprocket as close to the swinger pivot as is posasible in order to have as little chain slack variation as is possible and the other bonus has also been the ability to use a longer swingarm without stretching wheelbase win win
this change all started in motocross, during the long travel suspension revelution era 1974-1980

Offline Nilrog

  • Posts: 10
Re: '81 CB750KZ Brat
« Reply #11 on: Jan 04, 2016, 10:13:14 »
The added chain slack and swing angle will also most likely cause the chain to hit the frame coming off the front sprocket and the swing arm entering.

Offline Kezert

  • Posts: 9
Re: '81 CB750KZ Brat
« Reply #12 on: Jan 04, 2016, 13:45:10 »
Thanks for the support guys. Gonna make new shock risers and maybe some kind of roll tensioner.

Did a lot of work on the bike in the last couple weeks.

Read on the webs that CBR600 coils would be a great upgrade for the bike so I bought some. Coils came off a running bike and measured good on the multimeter.
You can use the original brackets from the CB750, you just have to drill a hole with thread in the frame to make them fit.
Or you could fabricate new brackets but thats a hell of a lot more work.

Also further assembled the engine.

Mounted the fenders, lights and the speedo.
Had to bend the headlight & speedo brackets a bit to fit.
Brackets will get a tan soon.

For the front turn signals I designed a simple bracket and got it cut so that they fit on the lower steering stem.
And I'm mounting the rear turn signals on the round bit of metal behind the rear shocks.
Had to buy some M12x1,25 thread for signals to make them fit, the original thread ends that came with the turn signals were too short.
Got on the lathe and drilled a hole in the thread for the wires.

Assembled the front brakes with brand new pistons and rubber rings.

Test fitted the exhaust and some other things.

Next up is wiring!

« Last Edit: Aug 02, 2018, 08:35:36 by Kezert »

Offline SilkySmooth750

  • Posts: 173
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    • 1979 CB750 "Silky"
Re: '81 CB750KZ Brat
« Reply #13 on: Feb 19, 2016, 12:48:26 »
Great progress!  I really liked your front blinker mount idea, very original!

Offline generalyen

  • Posts: 78
Re: '81 CB750KZ Brat
« Reply #14 on: Feb 20, 2016, 13:32:15 »
The bike us looking great, keep up the good work. Let me know if your ass slides around on seat when you really get on the throttle.  I've always wondered if that would be an issue on these brat bench seats.

Offline Kezert

  • Posts: 9
Re: '81 CB750KZ Brat
« Reply #15 on: Feb 22, 2016, 13:41:43 »
Thanks guys. Time for an update.
I honestly forgot to make some quality pictures off the process the last couple of weeks.
But here is what I've been doing the last couple of weeks.
PS; Haha, I'll let you know generalyen.

Bike is completely re-wired now with new Lithium Shorai battery, lights, flasher relay, handlebar controls,
starter button + ignition switch relocated in tank, Acewell speedometer, CBR coils etc. Got some little things left to do.

I used waterproof connectors and braided line where possible for a nice clean look.

Painted the exhaust and made a bracket for the Supertrapp muffler.

Installed the grips, clutch cable and gas cable. Brake system assembeld and bleeded. The choke has a new place on the steering stem plate.

I wasn't happy with the brown saddle so I turned it into a black leather saddle.
Made a new tank bolt to secure it to the frame. Takes little space in height so the saddle will fit nicely above it.

Tank has been sprayed. Here is a picture of how far I am now with the bike.

I need to do some small things like bracket for the brake lines, install buttons in tank, spray the emblems, make a chain guard thing, etc.
I'll keep you updated. Let me know what you think.

« Last Edit: Feb 24, 2016, 17:24:35 by Kezert »

Offline RichRoberts44

  • Posts: 40
Re: '81 CB750KZ Brat
« Reply #16 on: Feb 25, 2016, 09:08:48 »
Was the seat made custom or bought from somewhere?

Offline Kezert

  • Posts: 9
Re: '81 CB750KZ Brat
« Reply #17 on: Feb 25, 2016, 11:27:28 »
Seat was custom made

Offline Tune-A-Fishİ

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  • Posts: 6844
  • BOTM LOSER Proudly Deplorable
Re: '81 CB750KZ Brat
« Reply #18 on: Feb 25, 2016, 11:52:31 »
Needs a tire hugger unless it's a show bike.
"I didn't come here and I ain't leavin"  Willie Nelson

"love hard, live fast, die fun" Kacey Musgraves

"Like a Wreckin Ball!" Eric Church

Offline canyoncarver

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Re: '81 CB750KZ Brat
« Reply #19 on: Feb 25, 2016, 13:47:14 »
Needs a tire hugger unless it's a show bike.

Yep, something back there would be good.