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Author Topic: CB750F3 cafe build  (Read 13725 times)

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Offline KJ790

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CB750F3 cafe build
« on: November 01, 2011, 03:58:57 PM »
Thought I would start a thread documenting my build as I go. I picked up these 2 1978 CB750F3's the other day and I decided I want to build one into a cafe racer as a winter project. My plan is to go through the motor, bore it to an 836cc, port the head, and put in new valve guides (as well as cam chain and other necessary parts). I want to go with a black and white theme, but I'm still deciding on what should be black and what should be white.

The bike:





Dis-assembly begins:

« Last Edit: August 29, 2013, 06:24:17 PM by KJ790 »
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The most dangerous part of a motorcycle is the nut that connects the handlebars to the footpegs.

Offline Rigid

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Re: CB750F3 cafe build
« Reply #1 on: November 01, 2011, 04:03:24 PM »
Get them running and do the tune-up before you do anything else.  You need to know what you are dealing with as far as condition.  Do not assume engines are bad no matter how long they were inactive.  Looks like fun :-)
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Offline KJ790

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Re: CB750F3 cafe build
« Reply #2 on: November 01, 2011, 04:19:02 PM »
Yeah, I already got this one running, it runs pretty good despite not being started in over 5 years. After pulling the exhaust I see that I have at least one leaking valve seal, and I know that the stock valve guides on these bikes were notorious for having problems. I've built quite a few race engines and I just can't help trying to get a little more power out of everything I buy. I will do all of the engine work other than the boring myself. I think if I clean up the head a little and deshroud the valves it should run pretty good. I don't want to make it too unreliable, so I am not going to go crazy with this motor.
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Offline MCRider

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Re: CB750F3 cafe build
« Reply #3 on: November 01, 2011, 04:35:49 PM »
I think reliability is directly linked to RPM. If you build it to be used in the stock rpm ranges, making power between 5000 to 8000 RPM, it will last as long as a stocker, nearly, IMO.

My experience is with 2 836s and one 888. The 888 was by far the better machine logging 50,000 hard miles. had to park it for oil leaks, but it never burned a drop that I could tell. 

That was fun. Sigh.
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Offline brandEn

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Re: CB750F3 cafe build
« Reply #4 on: November 01, 2011, 05:59:14 PM »
Score! Two F3's!
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Offline KJ790

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Re: CB750F3 cafe build
« Reply #5 on: November 02, 2011, 03:46:02 PM »
It was unseasonably warm today, so I thought I would take advantage of it and get a little paint work done. The tank was in pretty rough shape on the outside, but is spotless on the inside:



After a lot of sanding, a little taping, a little bondo in some of the dents, and a lot more sanding... I finally got a good primer base on it:





I gave the side covers the same treatment. One of them was cracked a little so I used a little fiberglass to reinforce it.



I hoped to get the first base coat on today but ran out of time. It's supposed to be warm again tomorrow, so hopefully I can get out or work early enough to take advantage of that.

The headers also got sanded down and got the first coat of high temp header black on... they aren't the prettiest right now, but after another coat or two I think they will look pretty nice:

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Offline KJ790

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Re: CB750F3 cafe build
« Reply #6 on: November 03, 2011, 04:46:12 PM »
After looking through tons of pictures of bikes trying to get ideas for how to paint this thing, I finally came to a decision. I love the design of BrandEn's bike, but I wanted some lighter colors to get more contrast. I decided on going with a similar design as he used (hope you don't mind  ;D), but went with white and black. I got some paint down tonight on the tank and the side covers. I'm gonna carry the white and black theme through with the front and rear fenders being white as well.







I have a few spots that need touching up, then I have a lot of clear-coating and buffing to do, but the idea is there for now.
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Offline Imago

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Re: CB750F3 cafe build
« Reply #7 on: November 03, 2011, 04:56:37 PM »
That's looking great! Would the engine get a black/white treatment?
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Offline KJ790

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Re: CB750F3 cafe build
« Reply #8 on: November 03, 2011, 05:19:04 PM »
Quote from: Imago on November 03, 2011, 04:56:37 PM
That's looking great! Would the engine get a black/white treatment?

Thanks! I'm planning on doing the engine gloss black with the edges of the fins silver and a few polished accents. I plan on sanding the gold off of the original emblems and polishing them so they are black and silver as well. The gauges and headlight are going to get a black/white/silver treatment as well. I thought about doing the frame white, but now I'm thinking it might be better to just go black, it's easier to touch it up if I chip it while assembling.
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Offline Imago

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Re: CB750F3 cafe build
« Reply #9 on: November 03, 2011, 06:10:03 PM »
What are you using for paint (I'm curious about the engine too) and how is it applied... gun?
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Offline KJ790

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Re: CB750F3 cafe build
« Reply #10 on: November 03, 2011, 06:20:56 PM »
I'm actually used Rustoleum automotive enamel in a rattle can for the parts pictured. I used the same stuff when I built my last bike 2 years ago and it has held up great, I've spilled gas on it and everything. A lot of people knock the stuff, but with a few tricks you can get pretty good results with it. For the engine I'm going to powdercoat some parts and use high temp engine paint on others.
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Offline KJ790

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Re: CB750F3 cafe build
« Reply #11 on: November 05, 2011, 06:54:32 PM »
Did some more cleaning and degreasing today. Man is this thing covered in oil and grime! I want the engine to be somewhat clean before I pull it out of the frame. I also had some time to get the gauges painted. Now I need to find some different faces for the gauges, just have to decide if I want a white face or a black one.



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Offline KJ790

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Re: CB750F3 cafe build
« Reply #12 on: November 06, 2011, 12:19:22 PM »
Blacked out the front end today:



I also ran into a little unneeded setback. I'm trying to take advantage of the unusually warm weather and get as much painting done as possible. I hate having to heat the garage up in the winter to paint, so if I get most of the painting done now then when it is snowing outside I can just keep the garage at 50 and do the motor work and assembly. In my rush I put the next coat of paint on my front fender too soon and it curdled. Looks like I'm gonna have to sand it all off and start over... oh well.
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Offline KJ790

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Re: CB750F3 cafe build
« Reply #13 on: November 08, 2011, 08:06:39 PM »
Got some parts today, new throttle cables, clutch cable, and choke cable. Didn't have a ton of time today, but I got the front fender sanded and repainted, and continued taking things apart. New fork parts should be here friday so the front end should be back together this weekend. Won't be long and I'll have the motor out and will start digging in  :D
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Offline 4n2twstr

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Re: CB750F3 cafe build
« Reply #14 on: November 09, 2011, 12:27:31 PM »
hey, you got that seat from ebay/Vietnam yet?  I'm curious to see how it looks mounted...
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Offline KJ790

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Re: CB750F3 cafe build
« Reply #15 on: November 09, 2011, 04:39:11 PM »
Quote from: 4n2twstr on November 09, 2011, 12:27:31 PM
hey, you got that seat from ebay/Vietnam yet?  I'm curious to see how it looks mounted...

I ordered a seat from Carpy on Monday, I hope it's not coming from Vietnam  ;D

I got the swingarm off and cleaned it all up today. The bushings were actually in good shape. Once I find someone to give me a hand, the motor will be out:

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Offline Grabcon

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Re: CB750F3 cafe build
« Reply #16 on: November 09, 2011, 05:19:45 PM »
Taking the motor out by yourself at this point of the game is easy. Get a nice blanket to put on the floor, undo the motor mounts, lay the frame and motor on the righthand side and slide the frame off the motor. put the motor in in the reverse. I would wrap touch points on the frame to prevent scratching during reassembly.
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Offline Ninjatronica

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Re: CB750F3 cafe build
« Reply #17 on: November 10, 2011, 02:31:03 PM »
I'll be watching this thread closely. I've been eying a 78 and might scoop it up. I like what you're doing.
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Offline Blitzburgh207

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Re: CB750F3 cafe build
« Reply #18 on: November 10, 2011, 03:38:25 PM »
Me too!  8)
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Offline KJ790

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Re: CB750F3 cafe build
« Reply #19 on: November 10, 2011, 03:50:14 PM »
Thanks guys!

I did a little buffing and waxing on the parts I've painted tonight. The seat should be here early next week   :D





I am by no means a painter, so it's far from perfect... however I'm pretty happy with how it has turned out so far. A couple flaws here and there just add character  ;)
« Last Edit: November 10, 2011, 03:58:30 PM by KJ790 »
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Offline Blitzburgh207

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Re: CB750F3 cafe build
« Reply #20 on: November 11, 2011, 10:23:00 AM »
Looks good to me!  I'm diggin the tuxedo look haha!  8)
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Offline KJ790

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Re: CB750F3 cafe build
« Reply #21 on: November 11, 2011, 04:10:34 PM »
Ran into a snag tonight while taking the wheels apart before powdercoating. One of the studs that holds the rear brake rotor broke off.



I tried heating the hub and removing the rest of the stud with vice-grips, but it wouldn't budge. I decided to call it a night (after a few choice words) and give it another shot later. I will probably have to try cutting it off and drilling it out. If all else fails I can steal the wheel off of the other bike, though I would rather not.
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Offline Retro Rocket

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Re: CB750F3 cafe build
« Reply #22 on: November 11, 2011, 04:22:09 PM »
Cutting that stud off is doing it the hard way. I would soak it in something like penetrine then use some heat and a good set Vise clamps or do the old screw 2 nuts onto the left over stud and use the bottom nut to undo the stud {after applying heat}  ..... ;)
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Offline KJ790

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Re: CB750F3 cafe build
« Reply #23 on: November 11, 2011, 04:28:49 PM »
Yeah, I soaked it with PB blaster, figured I'll keep soaking it and let it sit for a day or two and let the PB do some work. I'm definitely going to give the heat and vice-grips another try before cutting and drilling. The stud broke at the base of the threads, so there's no threads to work with. I could run a tap on the stud and cut some threads into it... that's a good idea.

I'm not sure why it broke, I sprayed them all with PB blaster before trying to loosen any of them, and the rest all came off really easy. This one just broke as soon as I started to turn the wrench. My guess is the stud must have already been cracked or something.
« Last Edit: November 11, 2011, 04:30:33 PM by KJ790 »
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Offline brandEn

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Re: CB750F3 cafe build
« Reply #24 on: November 11, 2011, 04:29:01 PM »
I like your paint choice. I have always like white bikes. As for your stud, Retro has it right. I would soak it in some penetrant then hit it with some mapp gas and vice grips.
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