1980 CB750 “Beavertail” Cafe Build

[BeantownBeaverTail666]

Week 10 Engine Work + Frame help

Projects for the week:
Engine back from painter
Engine case closed
New piston rings
Electronics tray welded in
Tank mount welded in
Rear seat pin/mount welded in
Rear seat hoop welded to fit better
Frame back to powdercoater


The Cerakote came out great - it was recommended to me because of its increased durability and resistance to fuel/chemicals but also won’t retain too much heat like other coating methods on air cooled engines. Hopefully it will last a long time! Once the engine is all back together I will take better pictures of the coating.

In an earlier post I mentioned that I tested the resistance between the slip rings on the alternator rotor. The resistance was out of spec as it measured open with the ohmmeter. A new one was installed with the work done on the case. Hoping this engine operates like a 0 mile motor once I’m done!

I don’t have many photos of closing the engine case - just wanted to power through getting it done. I did have help with the case which was awesome to have more experienced eyes to bounce ideas off of.

Next step is getting the piston rings in order - filing and making sure the gap is within spec. Not really much to report on from that front.

I’m curious of everyones’ opinion about continuing to run this cam chain tensioner. I’ll likely just get it replaced but I’d like to know how others determine when it’s replaceable or able to still be used.

Also had some help creating the battery box for under the seat. I needed someone with more metal working tools/skills than I had. My highly complex cardboard box from earlier in the thread was used as the template. I also will use quick release push pins for the seat release which is the reason for the tab in the back of the battery box.

Fieldnotes:
-Cerakote is a good option for engine coating - chemical/abrasive resistant while allowing for heat release
-Need a good file for piston rings
-This is an example of the quick release pins for the seat

Upcoming:
Piston rings gapped/aligned
Pistons on
Cylinder Jugs on
Head on
Cams in
Valve adjustment

 

[Luis Etchenique]

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)
View attachment 15093
View attachment 15094
View attachment 15095

Who says you can’t use a Tiguan (aka Truckuan) to haul a future workbench!
View attachment 15096

Workbench construction and final product! First successful project of the build
View attachment 15097
View attachment 15098
View attachment 15099

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

best of luck, and … following !

 

[Luis Etchenique]

Week 10 Engine Work + Frame help

Projects for the week:
Engine back from painter
Engine case closed
New piston rings
Electronics tray welded in
Tank mount welded in
Rear seat pin/mount welded in
Rear seat hoop welded to fit better
Frame back to powdercoater


The Cerakote came out great - it was recommended to me because of its increased durability and resistance to fuel/chemicals but also won’t retain too much heat like other coating methods on air cooled engines. Hopefully it will last a long time! Once the engine is all back together I will take better pictures of the coating.

In an earlier post I mentioned that I tested the resistance between the slip rings on the alternator rotor. The resistance was out of spec as it measured open with the ohmmeter. A new one was installed with the work done on the case. Hoping this engine operates like a 0 mile motor once I’m done!

View attachment 18094
View attachment 18095

I don’t have many photos of closing the engine case - just wanted to power through getting it done. I did have help with the case which was awesome to have more experienced eyes to bounce ideas off of.

Next step is getting the piston rings in order - filing and making sure the gap is within spec. Not really much to report on from that front.

View attachment 18096
View attachment 18097

I’m curious of everyones’ opinion about continuing to run this cam chain tensioner. I’ll likely just get it replaced but I’d like to know how others determine when it’s replaceable or able to still be used.

View attachment 18098
View attachment 18099
View attachment 18100

Also had some help creating the battery box for under the seat. I needed someone with more metal working tools/skills than I had. My highly complex cardboard box from earlier in the thread was used as the template. I also will use quick release push pins for the seat release which is the reason for the tab in the back of the battery box.

View attachment 18101

Fieldnotes:
-Cerakote is a good option for engine coating - chemical/abrasive resistant while allowing for heat release
-Need a good file for piston rings
-This is an example of the quick release pins for the seat

Upcoming:
Piston rings gapped/aligned
Pistons on
Cylinder Jugs on
Head on
Cams in
Valve adjustment

GREAT WORK fabricating that electric junction box !

 

[Old_Crow]

As for the cam chain tensioner, I'd replace it. The cracks on the edges would do it for me. Actually, if I had the engine as far down as yours is, I'd replace it even if it didn't have the cracks. No use to go to all that work and use a part that might fail in another couple of thousand miles.

 

[BeantownBeaverTail666]

GREAT WORK fabricating that electric junction box !

Thank you! I appreciate the interest. More to come this weekend.

 

[BeantownBeaverTail666]

As for the cam chain tensioner, I'd replace it. The cracks on the edges would do it for me. Actually, if I had the engine as far down as yours is, I'd replace it even if it didn't have the cracks. No use to go to all that work and use a part that might fail in another couple of thousand miles.

That's what I'm thinking as well. I keep running into items where I get caught in the thought process of "while you're in there" but also don't want to just uselessly waste money. Thanks for the gut check!

 

[BeantownBeaverTail666]

Week 11 Engine Finalization!

Projects for the week:
Piston rings gapped/aligned
Pistons on
Cylinder Jugs on
Head on
Cams in
Valve adjustment

We’ve reached a monumental point of the build! I took on this project primarily to learn how to rebuild and assemble an engine. It’s been a huge learning curve so far but an awesome experience. The second goal of the build was to check off a bucket list item of restoring or reviving an old vehicle - we are getting close to that part.

Once the engine case was assembled I worked on gapping and aligning the piston rings properly. Only the oil control rings needed a tiny bit of material shaved off - luckily all other rings were right within spec and did not need much work. I used a handheld drill with a hone attachment to get some good cross-hatching on the cylinder walls. Once that was complete the pistons and new rings went onto the connecting rods. As expected it was a huge pain to get the cylinder jugs on. I used an adjustable hose clamp to compress the rings as well as some assembly lube to help slide the pistons up into the jugs. I wasnt sure that the rings would stay aligned as they were pressed and pushed into the jugs but just had to trust it at some point.

After the pistons were in, the cylinder head was pretty easy to get on as well - the biggest trouble I had was keeping the engine level and sturdy enough to work on while holding onto slippery and heavy components. I set the engine time and got the chain on - which was also very difficult. Had to walk away and take a breath several times before tossing the engine across the room . After everything was on and timing was set it looked like the cam was just slightly not level - after asking some friends/consulting youtube videos I decided this was as close as I could get and snugged everything up one final time. Making sure the two indents on the sprocket were level with the head felt very imprecise but it looked good when checked with a straight edge and my calipers.

I got the intake cam installed and once both cams were installed I turned the engine over a few times to make sure the timing marks all continued to match up after a few spins and to also make sure everything felt smooth - it was very smooth which was a huge relief.

After the cams were in and the engine was timed properly I began adjusting the valve shims. The valves were all redone - lapped/new components - so now it’s time to ensure all clearances are in spec. I used the below shim kit (as well as the shims included from the factory). I was able to get all valves in spec or very very close. Below are the values of my clearances in millimeters.

Here is the final product - not to shabby for my first go at it! Very excited to have this completed. As a novice engine builder this was a great learning experience and also very stressful. With every turn of a bolt I was waiting for a dreaded crack or mistake to occur. Already can’t wait to fill it with oil and turn it over - time to get this bike assembled and on the road!

Heres a before pic just for fun

Fieldnotes:

• Use piston to push rings into cylinder to get a good feeler gauge read - grooves in piston can be used as an unofficial level
• Adjustable hose clamp can be used to compress rings into cylinder
• Keep good record of shim size used in head so future adjustments can be made easier
• Valve clearances in manual are historically too tight - target .13 - .15mm

Upcoming:
Frame back from powdercoat
Going to see how much reassembly I can get done throughout the week...

 

[BeantownBeaverTail666]

Week 12/13 Frame back and reassembly madness

Projects for the week:
Frame back
Engine in
Carbs on
Front forks on
Rear suspension on
Front/Rear Wheels
Clip ons…on
Lots of front controls on/mocked up

Huge progress since I last posted - a lot of reassembly has been completed. I was moving pretty quickly and did not take enough pictures…lots of work was done very late at night as I was excited to see this project come to life.

Getting the engine in the frame was much easier than expected. I was able to get some help getting the engine on the ground and then just put the frame down over it and bolted things up in several places. The powdercoat on the frame look great and thankfully I didn’t scratch it up at all getting some pieces reassembled.

This is the first time getting the seat and tank mounted on the bike for a look. I really like how it’s still a pretty classic look to the bike even for a DOHC which tends to look more “modern” in my opinion. Really digging how this thing is coming together and all the hard work is beginning to pay off. This brown seat with the cross-stitching is what gave it the beavertail name.

The carbs were professionally cleaned and rejetted with a dynojet system for pods and a high flow exhaust. I did want to do them myself but since I'm learning a lot of this as I go I didn't have the time to learn the full disassembly/reassembly process with the carbs/didnt have the proper equipment. I plan to abandon the wrapped exhaust pipes idea and go for something a bit newer and shinier. I think that will flow better aesthetically…..and mechanically.

Didn’t have it in me to write a really long post this week - feel free to ask questions if you have any!

Photo dump (disclaimer - lots of items are mocked up - if they look funny it's just to see roughly how things will look/fit):

Fieldnotes:
-I felt myself start to move too quickly in the past few weeks and I don’t want things to get sloppy; time to slow down a bit
-Mocking up items on the bike can get dangerous as you run the risk of forgetting to officially tighten/torque items. All bolts should go on “race ready”.
-Need some warm dry weather to paint this tank!

Upcoming:
Wire it up!

 

[brettp]

Be aware, the lights from the LEDs on your speedo will bleed through to adjacent bulbs and make them appear to be lit up. For instance, your N light will make your high beam indicator appear to be lit also. You'll get used to it, though, and recognize what is bleed through and what is truly lit.

 

[BeantownBeaverTail666]

Huge updates - the bike is done aside from break-in and minor things that I probably forgot in my build list. With the warm weather here on the east coast (and now half the MC season gone) I was chugging away at finishing this thing and getting it on the road. I’m posting all final weeks at once with photos and not a ton of word vomit. I’d be happy to answer questions anyone has with their own build but if you’re anything like me you just want to see the progress in short bullets along with photos.

Week 14 5/28 Wiring Craziness

Drilled holes in bars for switches
Started by loosely running all M-unit inputs
Took pieces of OEM wiring harness (mainly ignition side)
Wired everything one circuit at a time - gauge gave me the most trouble
Installed custom headlight/mount
Cockpit view

/\ What was I saying about a clean workshop is important? lol

_______________________________________

Week 15 6/7 Wiring tidy up + Tank Paint

Finalize all wire routing and testing
Tank and seat mockup for motivation
New Ignition coils and wires installed (not shown)
Tank primer laid down
Green Laid down - I chose to go with Porsche Forest Green Metallic. It looks almost black in the shadows and slightly green in direct sun

Cleaned up the shop because it was getting crazy

_____________________________________

Week 16 6/14 Exhaust install/Miscellaneous

Install exhaust - went with a Delkevic and abandoned the wrapped exhaust
Sprayed clear on tank
Hand paint/mount logos
Had a mechanic check my work for sanity/carb sync run fuel lines/set idle
Getting there!

I test mounted the emblems and also plan to use trim liner around the edges to line the tank to "finish it a bit" this is the photo of no trim liner

Here is what it looks like with trim liner - let me know what you think!

______________________________________

Week 17 6/20 She’s Done!

First start in 18 years went well
Pulls hard, shifts well, brakes hard
Engine break in needed
Before and after shot
More pics to come!

Love seeing how far the shop has come and my first completed build inside.

 

[brettp]

The red plug wires are a nice touch. Beautiful bike.

 

[BeantownBeaverTail666]

The red plug wires are a nice touch. Beautiful bike.

Thank you Brett!

 

[Nylundarn]

Looking really nice! Do you think you will have any problems with ground clearance? I smacked my nice shiny fork brace on my first ride! Had to put the forks back in original triple tree position after that...

 

[BeantownBeaverTail666]

Looking really nice! Do you think you will have any problems with ground clearance? I smacked my nice shiny fork brace on my first ride! Had to put the forks back in original triple tree position after that...

The rear suspension was definitely too short - I measured the stock suspension and probably didnt take into account how much it was sagging. I installed new rear suspension that is about 2 inches taller.

As for the front, it hasnt given me any issues yet and there are some pretty haggard roads around me. I do think it's too soft though and doesnt spring back as much as it should....i might either add more fork oil or just drain the current amount and re-add to check my measurements.

 

[Nylundarn]

The rear suspension was definitely too short - I measured the stock suspension and probably didnt take into account how much it was sagging. I installed new rear suspension that is about 2 inches taller.

As for the front, it hasnt given me any issues yet and there are some pretty haggard roads around me. I do think it's too soft though and doesnt spring back as much as it should....i might either add more fork oil or just drain the current amount and re-add to check my measurements.

Sounds good! Maybe I have to take a look at my forks...

 

[BeantownBeaverTail666]

Before and after for fun:

Other photo because it just looked mean in this light:

New Suspension raising up the rear - front is still down:

 

[brettp]

Beautiful!
How did jetting with the pods go?

 

[Loose Chain]

The cafe look is not really my thing but good job there.

 

[BeantownBeaverTail666]

Beautiful!
How did jetting with the pods go?

Not too bad, I went Stage 1 dynojet. It starts just fine with choke and then feels pretty smooth while riding. The one problem I'm having is once the engine is warmed up it doesn't idle very well. I've adjusted the idle speed screw a few times to increase or decrease and it's getting a bit closer. Once the engine is warm I'll pull the clutch in to stop/turn/etc and the bike will either die slowly or idle at about 1500 - 2000 rpm. Not very fun but it's getting there. Compression numbers are coming up while the rings/engine breaks in so I think that is throwing a wrench in the works while tuning.

If you have experience with the idle adjustments I am all ears!

 

[brettp]

Sounds too lean at the bottom end, then. How many turns is your mixture screw out?