Author Topic: Been Keeping Busy - DOHC 750C build (Read 15938 times)

mono · « **on:** September 11, 2012, 08:51:34 AM »

back in march i picked up an '81 750 Custom from a buddy's dad. the bike had been left sitting behind the house next to a woodpile for 15 years. only had 4100 miles on it. for $300 i could not pass it up. i figured this would be a great bike to experiment with since it was cheap, relatively common, and really unexceptional in stock format.

I wanted to do a cafe' racer build, but this isn't really the bike for such a project. however, i'm still going to give it as close to a cafe' style that i can.

here's my before/during pic:

mono · « **Reply #1 on:** September 11, 2012, 09:54:04 AM »

the tank is going to stay flat black- it'll get repainted again after i coat the inside of the very rusty tank. there are a handful of pinholes, but all in all it's pretty sturdy still.

i did lower the headlight too, in what i thought was a pretty clever move. i actually inverted the whole headlight assembly. the "ears" that the headlight mounts to were very high up on the sleeves, so i cut off the turn signal mounts at the bottom of the sleeves and flipped the whole rig over

i was able to keep the rubber "seals" that go at the top and bottom, and because of the way the headlight bucket is contoured, it actually hangs over the crossbar that bears the HONDA emblem. took it down about 3.5 inches, and provides a much better profile IMO.

I'm also switching to a single gauge - just the speedo - and the space that i've created between the top triple and the headlight will allow the gauge to sit far lower also. i'll just have to fashion a bracket for it.

the ignition will also be moved to somewhere more out-of-the-way, which is going to involve some wiring and some kind of mounting bracket - hopefully a non-welding solution makes itself apparent.

i'm also going to be tacking the task of making a seat. i'd like to get my hands on another seat pan and keep the original seat (it's a nice 2-up seat), but fabbing one from scratch is something that may be fun. luckily i'm still on good terms with the ex-girlfriend, who has some mad sewing skills and said that if i designed the seat and foam, she could make a pattern and sew it up no problem. hooray for diplomacy!

mono · « **Reply #2 on:** September 20, 2012, 09:25:45 AM »

to simplify the front end, I removed the fusebox and cut off the mounting bracket that was cast as part of the handlebar clamp. then i made an enclosure for LED indicator lights to replace the hideous, bulky stock assembly. i made it out of sheet brass and soldered it with silver solder (w00t for having a jewelry studio). it fits snugly into the recessed area from where i cut off the fuse box mount.

painting it black, i think.

mono · « **Reply #3 on:** September 21, 2012, 06:44:57 AM »

last night i finished painting the housing for my indicator lights - here's a mock-up. now i need to trim down the wiring harness and patch in my new wires. i'll have to get some kind of connectors... probably some bullet connectors, or maybe a modern clip-connector that i'll mount in the headlight bucket.

mono · « **Reply #4 on:** September 21, 2012, 06:46:51 AM »

and another view:

Killer Canary · « **Reply #5 on:** September 21, 2012, 08:48:05 AM »

I'm curious to see what you can make of this. It seems that the C model must have sold in more numbers than all the others. They're all over the place! If something nice can be made of one, that would open up a whole new market. G'luck!

mono · « **Reply #6 on:** September 21, 2012, 09:01:28 AM »

Thanks, Killer. Yeah, there were TONS of these Customs made, and because of the contoured frame and the comstar wheels, they aren't really "cafe" standard bikes. people make some sweet choppers out of them - they look good hard-tailed with a springer seat - but i'm trying to go for something more unique i guess. we'll see - it's going to be a long-term project in order to make it look nothing like itself.

mono · « **Reply #7 on:** October 01, 2012, 09:03:33 AM »

over the weekend i polished up the 18" rear that i picked up, and decided to see if it would fit.

removed the comstar 16" wheel and switched the sprocket out. used the spacers from the comstar, and BAM! fits perfectly, nice and centered (yes, the racing slick is getting replaced with an actual tire). kind of surprised, very happy. i will have to swap the center hub, though -- the braking surface is very rusty. i'm hoping the hub from the 17" rear is in better shape - going to pull it this week and take a peek.

next is to tackle the front -- i'm hoping there's a way (without machining) for me to fit up the dual discs from the comstar onto the 19" spoked front wheel, and that the axle will mount correctly.

enough chatter, though - PIC!

mono · « **Reply #8 on:** October 02, 2012, 05:31:57 PM »

Got quite a bit done tonight. Remove the front wheel from the 81 and off of the 77 750. got the rotors off of both of them but I couldn't get the axle out of the 77 front wheel. It's just a little too rusty. So I shot it with a bunch of PB blaster and I'm going to let it sit for a while before I try to free it up. I also found a forum thread where a guy tried the swap and apparently he used 2 front rotors from a 550 on the 750 spoke hub. But there is a difference of 2 millimeters in width between the 550 and the 81 750 rotors so apparently you have to machine down the brake mounts on the forks to allow for this difference. Going to price some 550 rotors and perhaps consider getting the holes on the 81 750 rotors filled in and then re drilled to accommodate 6 bolt s as opposed to 5.

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Killer Canary · « **Reply #9 on:** October 02, 2012, 05:51:21 PM »

Do you have access to a milling machine and dividing head?

mono · « **Reply #10 on:** October 04, 2012, 05:52:25 AM »

Quote from: Killer Canary on October 02, 2012, 05:51:21 PM

Do you have access to a milling machine and dividing head?

i personally do not, but i have a friend who's capable of doing the work for me. he's quite good and knows bikes.

I'm going to do some measuring before i jump into anything. i realize if i want to retain the C discs that i'll have to remove some material (just a smidgeon) so they fit on the K hub. I would honestly prefer this route, as it seems like there'd be less fiddling around with clearances, but who knows.

mono · « **Reply #11 on:** October 12, 2012, 06:32:41 PM »

okay well I had to give up on the idea of doing the dual front disc brakes connected to the spoke rims. I ended up getting the engine freed up on the bike that has the spoked wheels. So its back to the comstar wheels. Anyway tonight I started a pine sol soak on the carbs from the 81 750. Here's a pic of my carb soup. They were pretty horrible and corroded and had all kinds of crap in there. They've been soaking for about 3 hours and I hit them with a toothbrush. I'll probably let them soak for another few days.

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mono · « **Reply #12 on:** October 14, 2012, 10:21:02 AM »

Just went and picked up some sexy new hardware for my carbs. Whoever rebuilt the carbs for the PO did a great job of f**king up all the Phillips screw heads. They were all really rusty anyways though.

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mono · « **Reply #13 on:** May 08, 2013, 09:37:03 AM »

more of a note to self -- not much progress on this build other than polishing some stuff.

after picking up yet another roller over the winter, I'm back to the spoked rims for this build, which is cool. but that means i either need to go to a single front disc or continue with the dual-disc conversion. struggling with the decision.

in the meantime, need to prioritize my tasks:

- drop engine
- rebuild to "roller"
- design new seat
- repaint frame.
- reinstall engine
- soda blast carbs (contact Nick), rebuild, install
- figure out electrical / simplify?

70CB750 · « **Reply #14 on:** May 08, 2013, 10:06:59 AM »

Quote from: mono on September 21, 2012, 06:44:57 AM

last night i finished painting the housing for my indicator lights - here's a mock-up. now i need to trim down the wiring harness and patch in my new wires. i'll have to get some kind of connectors... probably some bullet connectors, or maybe a modern clip-connector that i'll mount in the headlight bucket.

Where are you gonna have the key ignition switch?

Reason I am asking is I am presently mocking up K3 control lights with F3 top fork bracket and igniton switch and they don't line up the way I would like them to.

mono · « **Reply #15 on:** May 08, 2013, 11:07:58 AM »

well, my current plan is to have a keyless ignition (RFID) -- but if i do end up mounting a keyed ignition, it'll be somewhere around where the current "storage area" is on the left side. would probably have to weld a tab on.

70CB750 · « **Reply #16 on:** May 08, 2013, 11:15:34 AM »

I see, thank you.

Elan · « **Reply #17 on:** May 08, 2013, 02:07:56 PM »

Quote from: mono on October 14, 2012, 10:21:02 AM

Just went and picked up some sexy new hardware for my carbs. Whoever rebuilt the carbs for the PO did a great job of f**king up all the Phillips screw heads. They were all really rusty anyways though.

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Are those black oxide finish screws? You may need to paint them or something, I used black oxide screws and they were all rust in a few months. Just a heads up

mono · « **Reply #18 on:** May 08, 2013, 02:40:09 PM »

Oh really? Thanks for the heads up - yes they are. I haven't used them yet - I'll just order chromed ones!

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mono · « **Reply #19 on:** August 23, 2013, 11:53:29 AM »

Been getting a second wind on this since the 550 has been quite reliable all summer so far. we had a few cooler days there for a while so i've been doing some polishing on the engine covers and i painted the valve cover a couple days ago (Rustolem Engine Enamel). i was in the process of polishing the valve cover, however it's shape did not lend itself to being easily polished, so i decided on the spraybomb. came out quite well - i'm really getting adept at using rattlecans lol. 3 heavy coats of paint, no sags, very minimal orange peel (looks just as good as any new car's factory paint). you can see the clutch cover on the other side is polished.

mono · « **Reply #20 on:** August 23, 2013, 05:25:26 PM »

Here's the other side:

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70CB750 · « **Reply #21 on:** August 24, 2013, 02:35:58 AM »

I like the shape of the engine, the narrow jugs and big head.

mono · « **Reply #22 on:** September 05, 2013, 06:06:23 PM »

Finally got the covers on the other side polished, and the engine half-ass painted. I'm not going for perfect, in fact I'd like it to look a bit "backyard mechanic", so it's good enough.

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mono · « **Reply #23 on:** September 11, 2013, 12:43:12 PM »

getting things mocked back up so i can figure out what's getting altered. i think at this point i'm going to leave the rear fender off of it, and use the mounting point at the end of the frame to attach a bracket which will hold the tail light and license plate holder.can't decide whether to chop or totally ignore the front fender. it's not structural on these bikes, so i can do either. i reallly want to drop the airbox out of the equation, but the CV carbs are notoriously hard to tune is that's done. i'm going to leave it on for now, but i had a science epiphany earlier that i need to try out.

mono · « **Reply #24 on:** September 16, 2013, 04:43:11 PM »

Waiting on my tail light to get here, still searching for the correct turn signals. With the super bike bars I'm really going to need rear sets (hard task for this bike) but I'll figure something out.

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Author Topic: Been Keeping Busy - DOHC 750C build (Read 15938 times)