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Author Topic: 1980 CB750C First build  (Read 661 times)

Offline demitrix

  • Posts: 7
1980 CB750C First build
« on: Jun 17, 2017, 11:12:51 »
Who could've imagined another CB750 project? I must be crazy to attempt such a rare project. Anyhow I wanted a place to document my progress, get motivation, and help on the things I'm a little over my head on. Here's the donor for my attempt at glory.

PO said the bike was running about a year ago but he never did anything past getting it started. My plan for the time being is to deconstruct and start building from the motor out. Got most of the bike apart last night. Pulling the engine tonight. I have a Vesrah gasket kit and K&L oil seals on their way, and will start tearing into the motor Sunday. At a minimum (and hopefully that minimum is actually the maximum) I plan on new gaskets, new rings, and a good deep cleaning. If I come across anything out of spec along the journey I will be replacing it as well (here's to hoping my tensioner isn't cracked and valves aren't trash). I didn't do a compression test because I planned on doing all the gaskets regardless, didn't want a 37 year old motor leaking oil all over itself after I clean it up, since I will that far into the motor just as well to do piston rings and not have to worry about it.

The final plan includes full suspension from a 2005 GSX-R, still reading on the swingarm geometry (any local experts feel free to chime in with something other than "you're geometry is all wrong"), lot's of toys from Motogadget, Cognito moto, and CycleX, and a few custom things here and there.

Offline _amz95

  • Posts: 8
Re: 1980 CB750C First build
« Reply #1 on: Jun 17, 2017, 11:22:51 »
Check mine 1981 cb750 mybe it will help u


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Offline demitrix

  • Posts: 7
Re: 1980 CB750C First build
« Reply #2 on: Jun 19, 2017, 12:40:29 »
Started tearing off the parts I won't need over the weekend. Got a little anxious and wanted to test fit the swingarm. Width is good, will need some spacers on the sides and for the stock bolt. Biggest struggle like all the others is figure out the rear suspension. Only real issue I've spotted so far is that he swing arm is going to hit the trans casing. Not sure how I am going to clear that up at the time being. Spent all day yesterday helping a buddy try to get his Vulcan 500 up and running after the PO left it sit outside for a few years.


Offline demitrix

  • Posts: 7
Re: 1980 CB750C First build
« Reply #3 on: Jun 26, 2017, 18:57:51 »
Motor is out. Started cleaning today. I think the 3M pads I got are a little too abrasive. Planning on painting the motor anyhow so not too worried.



Continued into dismantling the motor to find what needs replaced. By the luck of Odin it looks like both of my tensioners are in good shape. The cam chain guide however is cracked.

Offline demitrix

  • Posts: 7
Re: 1980 CB750C First build
« Reply #4 on: Jun 28, 2017, 12:33:07 »
Valves are out. I'm new to rebuilding, but I think the valves are in fair shape. I need to clean them up, especially the exhaust valves. Photo of the intake valve is after about 3 minutes with a hand held wore brush.

Exhaust



Intake


Offline arieon69

  • Posts: 23
Re: 1980 CB750C First build
« Reply #5 on: Jul 01, 2017, 08:46:43 »
you're diving right in! thats what I like to see. Don't lose momentum.

Offline Cookie

  • Posts: 545
  • God help the child who grows out of everything
Re: 1980 CB750C First build
« Reply #6 on: Jul 01, 2017, 09:22:24 »
Nice stuff demrtrix.  May I suggest you do yourself a favour and sign up over at www.cb750c.com and download yourself the factory service manual and all the relevant addenda for your bike's model year. It'll make your life worlds easier having all the factory specs and procedures ready to hand.
The guys over there are mostly of the restoration/preservation mindset, and so they're not overly receptive to us cafe/custom guys, but if you have ANY teoubles or hiccups they've probably got an answer.

As previously mentioned, nice stuff so far!
* Insert something witty here *

81 CB750C
84 Tempter - well, most of it...

Offline djmaynard

  • Posts: 163
Re: 1980 CB750C First build
« Reply #7 on: Jul 02, 2017, 20:19:16 »
Looking great! I have a 77 CB750k and I just walk by it daily thinking I want to start that project. (I am drywalling my 1900 sq ft baseman solo with 3 kids under 5 and one due August so it's not like I'm sitting around). But love projects


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Offline demitrix

  • Posts: 7
Re: 1980 CB750C First build
« Reply #8 on: Jul 03, 2017, 19:10:51 »
Yup already grabbed a copy the manual. It's a little vague on somethings but I am making my way. Don't have any new photos, but the valves are now cleaned and the cylinders are pulled. Plan was originally to do new rings, at a 50/50 right now whether to go ahead with that route. Going to spec the ones in service now cause at first glance they seem almost new.

Still searching for an easy way to clean up all the parts for paint. No access to a soda blaster and simple green seems about as effective as plain water.

Offline J-Rod10

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Re: 1980 CB750C First build
« Reply #9 on: Jul 04, 2017, 16:02:08 »
Take the top end apart, spray it with purple power, and blast it at a car wash. Bottom end will have to be washed by hand, unless you are splitting cases.