CB750F3 Project: Burning Spear

Picked up a 1973 CB750 for less than scrap prices a little while ago. It had been ridden hard and left for dead in storage, then moved to a backyard where I found it. Definitely will have to put some work into this before it will become road worthy.

This is my first project as well as my first bike. Yes I know that most barnfinds cost over a grand to get started. I am actually more interested in building and learning about this machine than riding it right now. There will be time to ride in the future but will probably have another project by then. Hopefully with help from the fine folks here at DoTheTonforums and the Honda service manual, I will have this kitten purring in time.

There are a few issues that have to be dealt with, my short term goal is to get it running, ride it for a season, take it apart for a shave, paint and polish, put it back together again and enjoy.





As I brought it home. First thing to go would be the sissy bar. Paint will not be so purple in the future as well.



4 in 1 header pipes are crudely cut off just past the collectors. They are also pounded flat on the bottom. Not sure if they are worth saving, probably just keep them for welding practice in the future. Definitely going on the 'Maybe' pile for now.



I had to take a before photo



Few days later




Some of the wiring was held in place with string



This is why I am going with new wiring, that and the liberal use of red automotive wire with hand twisted and electrical taped connectors.



Had to drill off the handle bar switch gear on both sides.





Left over damage from previous side car conversion. Looking at right side passenger peg triangle. I debated restoring this frame to stock specs but will likely cut off these triangles in the future for a cleaner look.





Now this is what you call a booger assed weld job. I don't know what to say but the weld should probably be fused to something





Clip for front fender support is broken. Anybody know if these are still available? Will probably not be putting the fender back on the bike, will go in the 'for sale' pile



Found a spare motor on kijiji, the motor in the bike had a hole in front of the sprocket. Will get this one running in the bike and will have a machine shop weld up the original case. Original motor will be rebuilt or sold/bartered for parts.



Pistons on spare motor look like they should.







Bores look good, will just give a quick hone



Will take these apart and try to get everything blasted clean.

That is all I have for today, have to borrow some tools from my brother to remove valves this week.

*****Now using a 1978 F frame and parts. The 1973 has damaged engine cases, engine will be used for spare parts. The frame is too rough and damaged from what appears to be a botched sidecar installation, the large dent on the down tube just bothers me. Not interested in using JB Weld to fill the dents, instead will be lopping off the neck to use in a future project. The rest of the good parts will be sold to recoup my investment.*****

Re: CB750K3 Project: Burning Spear



Bought an impact screwdriver a couple of weekends ago, worked great on freeing up the screws on the clutch case including one that was badly stripped. It was almost round, loaded the robertson head in the impact, gave it a few taps with a hammer and out it came. Not so lucky with one exhaust flange. Well the exhaust flange is ok but I bent the phillips head screwdriver bit. Looks like soft serve ice cream, sorta.


What I started with



Chewed up wiring harness, this thing was hacked apart so much, lets me know why it was not being ridden, that and the hole in the crankcase.



If I can trick a couple of people into helping me remove the motor, I would be in an even better place. Still waiting for my brother to bring his motorcycle jack here, do not have a center stand. Do not want to lay the frame down to remove the engine because the sidecar mounts do not allow the frame to get close enough to touch the ground. Do not want to risk damaging this motor more than it is already. Want to remove the forks and strip the frame bare.

Hope to get more pictures up soon, have to clean up my workspace.

Also would like to pull the valves soon and try to get some work done on my engine cases(both sets need welding/machine work)

Re: CB750K3 Project: Burning Spear

Took a bit of time and worked on my Skate yesterday, Did not do much, just removed a lot of crud from the frame for the most part. Also decided to do something about the mouldy rusty seat that came with the bike. Took it apart to see if there was anything I can salvage but sadly the only think worth saving was the document pouch. Ended up throwing it in the bin and my garage smelled better instantly.

Removed the Motor







Really need to invest in shelving as I am running out of floor space at an alarming rate.













Some of the crud I have been scraping off these filthy bones. Self oiling chain system is a little too messy for me, have to do something about that.



Another pic of the damaged passenger peg triangle that will probably be removed in time, plan on running a solo seat with rearsets.





Here we have the mouldy, rusty, smelly, oversized seat section.








Not much good here



Or here


And some shots before cleaning











Still have to take pictures of it cleaned up but I may just start tearing it down further, have to drain the forks and remove rear wheel, swingarm, etc., then time to decide on paint or powder.

That is it for now everybody, getting married to my lovely lady this weekend and will be in Europe for the next couple of weeks. Not sure if I will get another post in before then, hope to get back to this project shortly after returning from our honeymoon.

Re: CB750K3 Project: Burning Spear

Been back from vacation for a little while now and wanted to check in.

Had and amazing time in Paris and Amsterdam. Feel truly blessed to be able to visit other parts of the world, meet new friends, and have new experiences.

Have not touched the bike much since getting back but I have removed the rear wheel swing arm combo and the forks.

My plan was to remove the bearing races from the frame as I would like to change the bearings before reassembly. I can knock the top one out no problem but the bottom race is not as simple. I tried to use a long screwdriver but there is not enough contact area for the screwdriver. Might have to bring it somewhere to remove it but would rather do it my self. What is the proper way to remove them? Heat? Grind a groove in the bearing for the screwdriver to catch?

Here a couple of pics of progress


Brakes


Swingarm and rear wheel

The rims look like they could use some new spokes and a good polish. Might try some wider rims if it will work, I want a 160 rear tire.

Will take more frame pics in a few days.

Re: CB750K3 Project: Burning Spear

Has been a few months since I have updated this thread and for most of the time, the bike has just sat lonely in the corner of the garage while I worked on other projects around the house and garden. In addition, the motor that came with the bike has a nasty hole in the lower case caused by a loose chain I assume.

Because of this, I had been seeking a replacement motor at a reasonable cost. I ended up with a second motor that also had problems with the upper case that made it also useless. Not too mad about that because I got the second motor for a song and now have more extra motor parts than I hope to ever need.

Still needing a running motor, I answered an ad on Kijiji and purchased a 1978 cb750F3 project bike that had been disassembled and packed in bins. My original intention was to take the motor and small parts for the K3, then sell the extra parts to offset the cost of the parts bike. Seeing how the F3 came with every part needed, I decided I will rebuild it before completing the K3

Got the frame, tank and various bins of parts to my house then decided to not use the motor in the K3.

Instead I will be building the F3 and the K3 will go on the backburner while I try to source yet another motor or set of cases that I can use in lieu of the 2 damaged sets I currently own.

Because of this, my plans for the K3 have also changed slightly. Originally, the plan was to build a solo seat bike and get rid of the passenger triangle mounts. Now that I have a second bike, the K3 will remain a 2 up bike. I will have to remove and replace some of the tubes on the right side pass triangle because of the #$%* welds from when there was a sidecar welded on the frame.

Will go a little larger budget than I had originally planned and I will also take more time to make it right.


My wheel collection, 1 set spokes, 1 set cornstars, cbr600f4i rear wheel and there is a cb350 drum brake front wheel in the mix somewhere.


2 frames, K and F with tanks


3 motors buried in this pile of poop, not much room left with 2 bikes in parts. Give credit to all those guys who are working in a shed or out of the back seat of their pick up trucks.


SuperSport badge

Re: CB750K3 Project: Burning Spear

Looking good so far! Keep it up and look forward to seeing where you go with the build!

Re: CB750K3 Project: Burning Spear

ManxieRacer said:

Looking good so far! Keep it up and look forward to seeing where you go with the build!

Click to expand...

Thanks for posting Ryan, I am also interested in seeing where this build will go.

Was originally going for a solo seat cafe style custom, but find I keep changing my mind every time I see an inspiring build, I am sure you know how it goes.

Bought the second bike(F3) in boxes for a price I absolutely could not refuse. That actually helped me decide to build the K3 to more of a brat style 2 up cruiser. Will build the F3 first since it does not need as many parts as the K3, which still needs lower cases, fork tubes etc. That will buy me some time to find (and fund) some parts needed to build the K3 how I see it in my head although that vision is constantly changing. Also seriously contemplating purchasing a TIG welder at the moment.

Just won an ebay seat hoop and piston rings for the F3, will be slowly rebuilding the motor over the winter and spring as funds and time permits.

Will be sure to check out your build, love the XS Yammies!

Re: CB750K3 Project: Burning Spear

I know what you mean about changing the vision. I did the same but now I've settled on something it makes it easier to get to the end goal. Ultimately the first goal should be to get it roadworthy, then the cosmetics can come later

My build isn't going so great at the moment, discovered I have a large overbore (900cc from a 750 block!) and waiting for various machine shops to get the piston rings and gaskets needed to button it all back up.

There has been a few changes on this project. I have decided to use a 1978 F3 that I picked up late last year. The main reason is because the engine and frame from the K3 both had problems. The frame has a dent in one of the down tubes that has bothered me since discovering it. The plan was to use heat and some persuasion to remove the dent, then fill with either lead or another filler that would work with powder coating. The bottom end casing had a hole in the usual place so that motor will be taken apart and parts sold. The frame may be used in a later project and the extra parts on hand will be used if needed, and sold if not needed.

Unfortunately the past winter has been far too cold for me to do much work in the garage. I have also been working outside over the coldest winter we have had in years so the last thing I wanted to do was go out to an unheated garage after a day of freezing my nards off. Instead I have ordered a few parts, gaskets, bolt kits that will be needed at some point down the road.

I have removed a few tabs from the frame, removed the bottom kick stand and fitted a seat hoop that I bought on ebay from harrisuluv. You may have also noticed the shock mounts have been removed, they will be replaced with new mounts in the same position as the old mounts.



Before


After, the hoop is not welded on right now but I am happy with the length.

Have also acquired a spoke CB750f1 rear wheel and brake bracket that may or may not be used for this project. If used, will be going to a wider rim front and rear as I would like to run a 150 or possibly 160 in the rear, 120 front, 17's or 18's, not sure yet but may have to look into other swingarm options that will accommodate a larger tire. From what I have read, it is a bit sketchy trying to mate a wide tire to the stock swingarm, do not want to modify it to fit.

Tore the engine down to an empty case, was less scary than I thought it would be. Only thing left is to remove the countershaft bearing. The cases will likely be powdercoated after being cleaned.


Upper Case Bolts


Lower Case Bolts

Have not had much time to work on this, when I do have time, there is no money. Either way, I still enjoy my time spinning wrenches at my own pace. Sometimes the garage is the only place where my opinion matters, it is the place I plan for battle, as well as the place to lick my wounds and recover. It is the place I go when I need a minute to calm down.


Got this guy completely broken down. I was contemplating just doing the top end, decided to open the cases up to inspect the gears. There is a good chance this motor will be powder coated in the near future so I spent a day scrubbing and rinsing. Pretty sure that all plugs and everything else has been removed, will give it a once over before it goes out for blast and powder.


This fell out of the motor once I separated the lower case assembly, anyone know where it goes? Will keep an eye out for it in the assembly manual.



After some scrubbing




Found a rear wheel that I might use on this project, might save it for another


Also trying to figure out what this is for, thought it was a wheel spacer.

Broke down the F1 wheel for cleaning and threw the rusty hoop in the garbage, I need to order the 6 bolts for the brake rotor. Might send this for powder and will be ordering a new rim.

As she sits today


Cordless drill and angle grinder to fab up some new shock mounts, the mounts are in the same place as stock.


GL1000 front end to compliment the F1 wheel, should I decide to use it on this project. Missing the bolts that mount the brackets to the forks, must order some although they seem to be discontinued most places. Anyone have an idea for a replacement? Pretty sure it is 'bad juju' to buy a used bolt for any part of a braking system. Should I just add this to my list of parts needed from CMSNL? Is there a hardware store solution that is less stressful and just as safe?

Will build 'er with the Comstar wheels, get it running and the bugs ironed out. Will decide later if I want to switch to the spoke wheels or save them for something else.

For now I am searching for engine bearings, seals and anything else I need for the bottom end.

hell of a project

Have not done much with this project over the last year because of other expensive home repair priorities and school. Got a deal on a welder at my local supplier so I got some welding done.


Made up some shock mounts, did not want to cut the stock mounts.


Welded up shock mounts and loop that came from ebay many moons ago. Also notice the cb900f piggyback shocks.


Also started to hammer out a seat pan, not sure how I will mount it, probably something simple.




Cognito Moto rearset mounts, I will have to get the swingarm bolt cut shortened and new threads cut. Will add that to the machine shop pile of parts.

Little more welding and maybe I can start to put it back together. I have a few changes coming soon.

Cool build man. Let me know if ya want to part with that GL1000 wheel.

Looking good man. You chose a ruster of a bike to fix up but you're on the right track. I think laying out the line of the bike like you have done is important to do every now and then to keep the motivation and inspiration high. Love it.