1980 CB750 “Beavertail” Cafe Build

[BeantownBeaverTail666]

Week 0 - Intros and Goals

What’s up everyone, I’m posting here to keep track of a build I’ve been planning out and to hopefully ask and answer some questions along the way. I recently began some online courses covering engine building and automotive wiring and thought a motorcycle might be a good low cost (hah yeah right) gateway into that world. I’ve done some basic maintenance on cars in the past but overall I’m just looking to see what I can do and maybe learn something about myself along the way.

A buddy of mine began a cafe racer project on a CB750F and after it’s been sitting for a while he said he would give me what he has (full bike with no motor). I plan to also buy a donor bike in any condition to pull parts from and rebuild the engine. Overall I’d like to build a classic looking cafe racer and leave no bolt unturned on this bike. The name "Beavertail" will make more sense once my vision comes to life and based on how some of the tail ends of these bikes look.

Projects for the week:
Shop clean out / prep
Workbench build
Start compiling a list of tools and supplies the shop will need

Photos:
Some before and afters of the shop (aka basement)

Who says you can’t use a Tiguan (aka Truckuan) to haul a future workbench!

Workbench construction and final product! First successful project of the build

Field notes:
Oxygen tanks are impossible to get rid of
Plywood is much more expensive than I thought
Drilling pocket holes is extremely satisfying

Upcoming this weekend:
Bike pickup 1980 CB750F
Donor bike drop-off 1980 CB750C
More shop tools/organize

 

[mrtwowheel]

Yeah, let's get started. Welcome to the forum.

 

[Loose Chain]

Good start

 

[brettp]

Looking forward to updates. Welcome from Florida!

 

[loxley007]

Fantastic stuff. I started around a year ago with zero workshop space, zero mechanical skills/experience and have now a decent home garage workshop space and have rebuilt the bike (full engine teardown - had a seized piston, hoop for cafe racer style, full electrics rewire, GSXR front end swap etc). It’s been a fun year of learning!!

I’ll follow your build with interest. By the way I’m posting on IG as the_cafe_racer_project

 

[BeantownBeaverTail666]

Thanks for the support and welcome messages everyone! Looking forward to getting the shop all together and most importantly getting some bikes in there this weekend. Lots of driving coming up - time to catch up on some audiobooks lol.

@loxley007 - Awesome build progress! Just checked out some insta pics. Did you teach yourself how to weld? Any resources (websites/courses/youtube channels) you recommend for learning to weld?

 

[loxley007]

Thanks for the support and welcome messages everyone! Looking forward to getting the shop all together and most importantly getting some bikes in there this weekend. Lots of driving coming up - time to catch up on some audiobooks lol.

@loxley007 - Awesome build progress! Just checked out some insta pics. Did you teach yourself how to weld? Any resources (websites/courses/youtube channels) you recommend for learning to weld?

Hi, thanks. I bought a MIG from a friend that was moving abroad, watched a few YouTube videos and realised that I needed some training so enrolled a course with The Machine Shop to understand the basics and get some feedback on where I was at. They are UK based though.

https://www.instagram.com/the_machine_shop_ltd?igsh=MXB5aTE3aWgyazBoag==

 

[BeantownBeaverTail666]

Week 1 Bike(s) Arrival and Shop Organize

Projects for the week
Bike Pickup
Parts Organize
Donor Bike Dropoff
More shop tools/organize

In just a week I’ve gone from never owning a motorcycle to owning two - I guess this is how it starts! I drove 6 hours round trip to pick up my friend’s bike. The day after I had the donor dropped off - busy weekend. The shop feels like it’s slowly coming together. After living in the city for the last 13 years I am extremely excited for my modest dusty basement workshop. Just having the option to take on a motorcycle build is exciting in itself.

A bit about the bikes:

1980 CB750C - Engine Donor - I purchased this bike for cheap off of FB marketplace. To my knowledge it has not been started in 15ish years - it's ready for a second chance on the road. The frame and engine have about 67k miles on them but the motor spins freely and aside from 40 years of road grit things look pretty okay. Once I get the motor out I’ll do a full teardown, paint and build it back up like it was new. Tank looks to be in good shape - if the paint wasnt so trashed then the candy muse red (I think that's the paint code name) might have been a cool option to keep.

This may become the offical "before" picture:

1980 CB750F - My friend gifted me his project after he hung up his wrenches and it sat for about 10 years. The bike comes with a frame that has already been modified with a rear hoop/detabbed. I have a feeling I will need to adjust the seat area/tank mount/add a battery box but we will cross those bridges when we get there - it will likely need to go back to bare metal and repowdercoated. Some welds looks a bit sketchy too. In addition to the frame there are loads of spare parts/set of wheels/forks/suspension/clip on handlebars/exhaust/carbs. His original goal was a tank with a rust patina but it was stored without a gas cap and now the interior of the tank has more "patina" than the rest of it....thankfully it was free so can't complain too much. I will likely end up using the tank from the donor bike.

The truckuan strikes again! There’s almost a full motorcycle packed in there.

If anyone has run spoked wheels, with dual front rotors, that did not involve a front end conversion - I'd be interested to learn more about what the set up looks like. Im assuming Cognito Moto or something more custom is the only option? I plan to use the Comstars for this build but would prefer a spoked wheel for future iterations.

Fieldnotes:
Workshop needs more light
Picking up the middle of someone else's project is more difficult than expected

Upcoming next week:
Front/Rear Brakes Disassemble/Clean
Forks Disassembly/Clean

 

[brettp]

I like it, looking forward to more progress!

 

[BeantownBeaverTail666]

Week 2 Brakes and Front Forks

Projects for the week
Rear Master Cyl Stripdown/Paint
Front Master Cyl Upgrade
Front Calipers Disassembly/Clean/New Seals
Rear Caliper Disassembly/Clean/New Seals
Front Fork(s) Disassembly/Clean/Paint

Brakes and front forks come first in the build. Both jobs seemed relatively easy and a good chance to get my feet wet and build up some confidence.

Brakes
Front and rear master cylinders both look like they have put some hard work in - time to relieve them of their duty. I upgraded the front master and rebuilt/repainted the rear. All caliper pistons were seized which was fun. I attached a brake line from the master to the caliper to build pressure and pop the pistons out so I can replace them along with all the rubber seals and clean the interior. I bought a brass wire wheel off Amazon to clean the area in the caliper where the piston sits, however, I received a brass colored steel wire wheel…almost ruined the inside of the caliper. Glad I noticed before I scuffed up the inner walls/changed the bore diameter.

I threw away the rear brake shim and then realized they’re pretty hard to find…lesson learned. Also the rear brake pistons are not made anymore (I think this is true?) and they are taller than the fronts - I found someone on ebay selling some replica’s and it looks to be pretty good quality and a snug fit.

Forks
Didn’t get a good before picture of the forks but the fork tubes had some surface rust on them and the paint on the lower fork assembly was chipped/faded. I drained what fluid was left in the forks which certainly was not fresh. The forks came to me off the bike which made unscrewing the top bolt pretty difficult. I was ready to buy a vice with a soft jaw attachment but realized through the forums that I could just put it back on the bike and crack it loose before moving forward. Another lesson learned - loosen bolts on the bike before fully disassembling.

After disassembly, I was able to get the fork seals out (huge pain) and then began stripping/repainting. I sanded off the old coating and used some high durability frame paint - hoping it is strong enough and doesn’t chip. It’s not very clear which side is top/bottom on the new seals. I used the old seals to help me figure it out - hopefully they were installed properly.

Overall, the front forks and braking system look and feel brand new. I’ll get some new brake lines and fittings later on down the line in the build.

Gotta show off my sad looking paintbooth:

Fieldnotes:
-Don’t throw out any parts until reassembly is complete
-CB750F Rear brake pistons are taller than fronts 38mm vs 41mm.
-Brake fluid sucks to work with

Upcoming:
Frame Clean
Seat Measurements
Electrics Tray Plan/Layout
Wiring Diagram

 

[BeantownBeaverTail666]

Week 3 Miscellaneous Prep

Projects for the week
Frame Clean
Seat Measurements
Electrics Tray Plan
Potential Electrics Tray layout
Battery/Wiring Arrival

The bike received a little bit less attention this week as work picked up and some family was visiting. Had a chance to get the frame out of the basement for a quick clean to remove about 10 years of dirt/dust and the inevitable mouse droppings. Not nearly as bad as cleaning the engine, I’m sure.

Loads of parts have begun to arrive and with the warmer weather as a teaser its fun to think about riding the bike once its done…still a long way to go though. I plan to run an M.unit for the additional functionality it provides as well as how simple it makes the wiring. I figured since this is my first big wiring overhaul it might be best to keep things relatively simple and easily research-able. Alongside the M.unit I’ll run a 801 Antigravity battery, Revival Cycles wiring kit and a Ricks Reg/Rec. Straight from the cafe racer playbook, right?

I took some measurements for the seat and still need to plan out my approach here. I don’t really have an interest in making a fully custom seat, but I am pretty picky and don’t want a cheap Amazon seat.

These measurements will also help me plan out my electronics tray. I would like to keep all electronics under the seat even if it is a bit more bulky and less streamlined than mounting the battery under the bike. Below is a picture of my very advanced CAD (Cardboard Aided Design) layout of the tray and components.

Photo Notes:
-I’m missing the spark units in this layout (I have them just left them in the shop)
-The Harry’s shaving cream cap will eventually be my starter solenoid
-I’d like to squash the Ricks unit on the inside but I’m not sure about overheating with the reg/rec, battery and spark units..
-The stock key barrel is huge - my hope was to keep this original but I may upgrade for a smaller unit
-I was hoping there would be space for a spare tools roll but I think this box will quickly fill up with wires - I also don't want any kind of short to happen while riding

Looking forward to some of the big projects coming up. I’ll have to enlist some help getting the engine out and I’m dying to clean and tear into it.

Fieldnotes:
-Not much to report this week

Upcoming:
Exhaust De-rust
Exhaust Paint
Exhaust Wrap
Engine Out!
Tank + Frame + Rear Suspension Mockup for fun

 

[Motogrady]

Interesting.

 

[BeantownBeaverTail666]

Interesting.

Thanks!

 

[BeantownBeaverTail666]

Week 4 Exhaust and Engine Time

Projects for the week
Exhaust De-rust
Exhaust Paint
Exhaust Wrap
Engine Out!
Tank + Frame + Rear Suspension Mockup for fun

I made - what feels like - big progress on the bike this week. I was able to get a buddy to help me get the engine out of the donor bike. I have never taken a motor out of a vehicle before so I wanted to move slowly and be cautious of the frame/bolts/cooling fins to avoid injury and anything breaking. Overall, it was not that difficult and the Clymer was a good resource to give us the proper order of operations for removal. The removable frame section was also a huge help - I’ve seen some YouTube videos of SOHC guys struggling to yank the engine out of there.

So far the engine looks to be in good shape - the oil didn’t look milky or have a shimmer to it which is good - we’ll see what the oil pan has to say but I’m confident she’s solid. Cleaning and degreasing the engine is going to be a nightmare I can already tell. I’m not sure how I’ll get all the dirt out between the cooling fins aside from using a steel bristle brush.

Next up I wanted to clean/de-rust/paint/wrap the exhaust. I’m not 100% sure I’ll end up using the stock exhaust but I wanted to try my hand at bringing it back to life and wrapping it. The headers had some surface rust up near the engine but nothing too bad. I put a flashlight inside the headers to see if there were any pinhole leaks where the rust got through but didn’t see anything of concern (I didnt get any good “before” photos). I bought a stripping disc that can be used with a drill and it’s a game changer - no need to buy a sander…yet.

As I move the exhaust around the workbench for grinding and sanding more and more mouse nests continue to fall out. I don’t think this exhaust has been used for probably 18-20 years…half the life of the bike!

The finished product looks…okay. The header’s came out great but going down the pipe it looks pretty bulky and not tight enough. I may try and tidy it up a bit but I’d hate to do it all over. It looks like the previous owner used a grinder to get the exhaust collars off…these look to be pretty hard to find online. I’m not sure if the stock ones will properly seal against the exhaust gasket with a gap from the grinder. Any recommendations where to source new ones are welcome!

To keep motivation up I put the frame on the jack and mocked up the tank and suspension. If you squint your eyes and tilt your head you can see a first glimpse of what the end product will look like. I’m looking forward to the bodywork portion of the build and working on the tank. Hopefully when the engine and/or wiring work gets overwhelming I can switch to the more creative and less technical projects to keep making progress. Time to start thinking of color schemes and the final “look” I’m going for. I keep switching back and forth between a few styles..

Fieldnotes:

• Use stripping discs for sanding/grinding
• Exhaust wrap is nasty stuff - use safety goggles/dust mask/gloves/throw away clothes
• Did not expect there to be asphalt/tar on the engine…cleaning should be fun

Upcoming:
Engine Clean Degrease
New Tires
Wheel Bearings
Wheel Sanding
Wheel Painting
New Sprocket
Rotor Deglaze
Rotor Paint

 

[Motogrady]

I sent you a link that might help you.
It’s in conversation feature.

If you can get Tools to respond over there that would be a good thing.

 

[mrtwowheel]

Just gotta say.........Wrap? Wrap screams NEWBIE.

 

[Motogrady]

Just gotta say.........Wrap? Wrap screams NEWBIE.

We all start somewhere.
I hope he pulls it off.

Dunno how many I’ve seen get halfway thru and then just disappear.
Read the thread, everything, even his work place is new.

Go for it beantown!

 

[mrtwowheel]

Those cylinders and crankcase are painted, you may not want to use a wire brush on them. I'd rather touch them up with a paint brush vs painting the whole engine. Diesel or mineral spirits are good first round degreasers.

 

[Motogrady]

The donors.

 

[Motogrady]

A cafe, with exhaust wrap, and a bobber.

Where will we end up?