Nov. 24th, 2022
Restoring 'Ruth' the 1974 Honda CB360.
Starting our love for motorcycles with a classic '70's racer...
Before starting, a few shoutouts — special thanks to Jack Whipple @ MIT D-Lab, Roberto Melendez, Pat + Mark @ the N51 Edgerton Shop, Sydney, and Maria who all helped with the knowledge or physical labor of getting this bike up and running. Also to the folks @ Common Motor for maintaining a lot of the knowledge-base and parts on these old Honda bikes.
Finally, thanks to Jordhana for selling me the bike at a pretty fair cost, I've always wanted an old CB and Ruth is a wonderful bike. Little bit of history, Ruth is a 1974 Honda CB360, Jordhana told me her name was Ruth and it didn't feel right to change it, Ruth is a great name anyways. She has 360cc's of displacement from a parallel twin engine and a 6-speed manual transmission. When new, the bike produced around 34HP, had a 0-60 time of about 7 seconds, and went on to a top speed of around 92mph.
This is the spreadsheet I used for tracking the restoration.
This is how Ruth looked when I first got her. The bike started and ran and everything, I was told of a few issues by the previous owner.
battery needs charging after each ride, drains fast (stator issue? rectifier issue?)
electric start not working, but kickstart working fine
idle speed of engine is a little low, can cut out if throttle isn't applied (adjust the screw? carb cleaning needed?)
broken odometer, no speedo
I got to inspecting the bike and found a few other things (the below photos show some of them). The full list is here.
the seat mount and gas tank mounts were 3D printed and they broke pretty much immediately as I removed them
the rear lights were not attached and don't work, the front turn signals also didn't work
the headlight only worked on low-beam not high beam
the condenser was so rusted I could barely see it
the wiring job was a little shoddy but functional, wiring harness was falling apart
rust in various places that needed cleaning, paint in various places was peeling
exhaust spacers were very very rusted, one was bent so probably need replacing
air filters were fine, but kinda large and I didn't like the look of them
the license plate mount got in the way of my legs
the point system wiring was a little tragic but functional
someone had cut off the back frame hoop and done a pretty shoddy job of it
I started by ripping out the entire wiring harness, this probably wasn't necessary but I wanted to replace it because some of the insulation was cracking and it would give me a deeper understanding of all the components on the bike and the ability to connect them up in a custom way that worked for me. The harness basically is just an efficient way to connect all the things that need connecting in the bike - we'll get back to this later.
Since the battery was dead and I still wanted to start the bike up, and I had removed the wiring harness I needed to power the engine ignition system with a power supply. Every IC engine ignites fuel when the cylinder is at the top of the combustion chamber driving the cylinder downwards to turn the main shaft. In old engines this is done using a point system. Here's a good video on how it works.
Points are spring loaded switches which switch on when each cylinder is at the top of the combustion chamber and the spark plug is supposed to fire. This sends 12V to the ignition coil. There is one point and one ignition coil for each spark plug in the motorcycle. The coils take the 12V turn it into like 12000-25000V to supply to the spark plug which sparks and ignites the fuel in the chamber. The condenser is basically a capacitor that sits across the negative of the coil input and ground that absorbs any transient voltage spikes protecting the coils and points from burning out.
The battery simply supplies voltage for this system to work, I replaced it with the power supply by attaching the black and white wires in this wiring diagram to the 12V on the power supply, and by attaching the negative of the power supply to the frame because most motorcycles ground all components to the frame to simplify wiring. This is how the spark plug gets a ground as well since there's only one wire going to it. The bike started after a few kicks.
Anyways, before we did anything else, I decided to clean, and de-rust.
So first I took off the exhausts, most of the electronics, the tank and seat, and covered the engine or carb holes with tape or tissue paper and gave the bike a good washing just to get off dirt and cob-webs. I did the washing, de-rusting, and painting first so no paint or anything got on the new wiring harness after it was installed. This process took a few days, there was a lot of rust on various parts of the bike, and I wanted to add paint coats to prevent them from re-rusting.
For the actual de-rusting we used a wire wheel, which is a fairly common technique and it worked rather well. Here's the before and after pictures of the rear maintenance stand with just the wire wheel. I wire-wheeled basically anything that showed significant rust damage with the exception of any part that should instead be replaced.
List of things that should likely be replaced if rusted too deeply
engine components, carb components, structural components (safety critical)
anything on the suspension or steering
drive components such as chain and sprockets
brake disks, brake calipers
anything on the fuel system such as valves
anything electrical, battery or similar
Most of the parts of Ruth were OK. It was mostly non-essential components or components like the stand and the under-belly pan that were rusting. I clean rust off of these components and sprayed them with protective coatings.
For the engine, I got clear engine enamel from Rust Oleum and sprayed both the engine and the carb with that. For the belly pan I got under-belly protective spay and used that. I also re-painted the exhausts with matte-black high heat exhaust paint.
Under belly stuff --> is rubberized for added protection
High heat exhaust stuff --> is a ceramic coating, can't use regular spray paint
Engine enamel --> needs to be rated to like 500°F or above
The wiring harness — now we get to the big boi, and this deserves its own section because we kinda changed a lot of things on the electrical system for this bike. The wiring is now simpler, with slightly less functionality, but totally works for the daily commuting and some longer drives I'll do on the bike. I'll try to explain what I did concisely, but in detail.
Let's start with what a typical motorcycle looks like and the wiring diagram of a CB360. The diagram was a real doozy to look at and figure out but basically each black square is a connector that we see on the wiring harness, and the colors of the wires in the diagram match the colors of the wires in the wiring harness. The harness you can buy from 4-into-1 pre-made.
Typical bike —
you have to supply 12V to the ignition coils and point system like we showed earlier
you have to power any lights and other accessories and make sure they're compatible with a 12V input (just typical car battery voltage)
the battery is charged up from generator/alternator/dynamometer/stator attached to the engine, the power passes through a voltage regulator before going to the battery
there's a starter solenoid which, when activated, powers an electric motor that rotates the crank-shaft of the engine to start the engine**
**This works because the point system of the engine gets power when the key is in the "on" position, and rotating the shaft causes the points to trigger the spark-plugs which initiates the first "explosion" of gasoline after which the engine is self-sustaining. So turning the key provides power to the point system and electronics by connecting the battery, and then the engine ignition button turns the starter motor while the button is held down. After the engine starts you can let go of the starter button and the alternator will power the engine, electronics, and charge the battery.
of course we want to control the lights, the starter, and the engine cut-off all from switches on the handle-bars, the battery should charge up automatically
Here's the wiring diagram we came up with. This was based on staring at the original wiring harness for a few hours and probing the outputs of switches with a multimeter to figure out what they did. Some notes.
Since the battery wasn't charging we determined the alternator or regulator was probably faulty, this is a solvable problem but for now we decided to eliminate it from the circuit and fully power the bike off a drill battery that we could swap quickly and charge easily. Digging the stator out of the transmission would be a little annoying so we decided not to do this right now, will come back to it later.
We also entirely ditched the electric starter for now for the same reason, we didn't want to dig the motor out of the transmission, we tested the leads to the motor and determined it was brunt out. Replacing the motor and adding a solenoid to actuate the motor would fix the electric start but we also will leave that for later.
The colors in the above diagram match the colors from the harness we got from 4-into-1 and the wiring diagram linked above. Some details.
The headlight switch is a two position switch, It takes 12V power in one lead and it outputs 12V to either the High-Beam or Low-Beam line. That means the headlight is always on.
The turn signal switch is a three-position switch. It takes 12V in and in the center position the switch outputs nothing. Flicking it left and right activates either the right or left turn signal by supplying power to the line. The turn signal relay is a bimetallic strip that turns on and off as current passes through it to make the signals blink.
For the condenser and point system, I kept everything the same, just cleaned up the wiring, cleaned off rust, and replaced the condenser.
The brake light works with switches that determine if the brake has been pressed. These connect the brake light negative to ground completing the circuit. If either the front or rear switch is pressed the circuit is completed.
For the entire new bike wiring harness, we decided to use the Deutsch autosport connectors built for racing cars. These are waterproof, durable connectors and we used these to replace the lower-quality white connectors already on the wiring harness and to replace some of the crimped connections for easier maintenance in the future.
First used a multimeter to probe all the outputs of the switches and label them
Then crimped the ends using this crimper and passed them into the connector housing
Covered the wiring with this cable cover for aesthetics and protection and then used heat-shrink at the top and bottom of the cable and over the connector to complete the harness section.
We repeated this for all the electronic devices already on the bike including the switches, and brake sensors.
For the main harness, we did a similar thing while matching connector pinouts. The front of the harness is the part where all the crimps come out in a big bundle because that part sits inside the headlight casing. We used this cable cover for the main part of the harness, and this cable cover for the smaller "branches." We connected the cable covers with wrapped electric tape with orange gaff tape over them. The gaff tape was secured using a small dot of super glue. We used heat shrink and autosport connectors on the end of the branches. The point system, and lights would be wired directly to the harness with solder joints.
To ground the wiring harness, we connected a green wire to the frame by using a self-tapping screw into the frame of the bike
Again, we used a multimeter to ensure all the wire colors were correct, and we labeled the wire colors with what they would be connected to
We mounted the wiring harness to the frame with zip-ties and then connected up the switches, and wired in the point system and engine electronics to the harness.
Before we connected the lights, the battery, or anything else we wanted to make sure the engine still ran with the new wiring. We cleaned up the point system wiring and connected the coils to the 12V line of the wiring harness and the green ground wire. Then, at the other end of the bike we attached the 12V line to the power supply, and the ground to a thick black wire that had been attached to the frame from before for ground.
We kickstarted the bike, and it ran.
Electrically the lights and battery are left
Mechanically we need to make mounts for the lights and battery, the tank, and a few other components, we still need to fix the back of the frame
We want to paint some things - I kinda like the gulf racing blue and orange
We got these upgraded air filters from common motor to replace the large boxy air filters on the bike with. These are sleeker and also re-usable since they use a metallic mesh. They were pretty easy to swap out.
We also got these exhaust collars, which go between the exhaust pipe and the exhaust holder acting as a spacer when tightening it onto the engine. Ours were just very rusted so we replaced them. Other than painting the exhaust from before we did very little to that system before it went back on the bike.
To fix the frame we used an angle grinder to grind down sharp edges in the back. I wanted to add a frame hoop so I looked for a hoop where the outer diameter of the hoop was slightly smaller than the inner diameter of the frame tubes, and one where the width of the hoop was similar to the width of the bike. The idea was to shove the ends of the hoop into the openings in the frame and secure it with bolts. The hoop wouldn't take forces it would just hold the rear brake lights.
I ended up getting this hoop which required just a small amount of bending to work. We took a butane torch and heated the middle of the tube and used a hammer to bend it. We then painted it a copper-gold color and pushed the ends into the open ends of the cut-off frame.
Finally, we drilled some holes and bolted the rear hoop on using two bolts per side.
For the lights, I went with these tiny LED turn signals, and for the rear ones I also got the turn signal/brake light combo. These lights have three wires, one for the turn light, one for the brake light, one for the ground wire. For the rear ones, I wired the brake light wire into 12V power so the rear red lights would always be on as running lights. The turn signal activates of course when the turn signal switch is activated.
For the front, we drilled two new holes in the front headlight casing to mount the front turn signals. For the back we made a steel adapter plate that screwed onto the rear shock mount and mounted the turn signals. We painted that with the gold color as well.
We didn't attach these lights to the wiring harness with crimps or solder we just used the bullet connectors that came with both the lights and the wiring harness. Since the wires are hidden this was good enough for us.
We also re-mounted the headlight.
On the headlight we added two pieces of Gaff tape for that classic cafe-racer style look. The tape was used when the racers had their front headlight covers made of glass and without windshields the tape was meant to protect the driver in case the headlight broke.
Now I just add it for that touch of history.
For the brake light, we chose this "bulb shaped" retro back light. To mount it we just drilled a hole in the back hoop and used a long bolt to screw it in with a lock nut. The wiring took a little probing of the harness, the rear brake switch wires are very close to the rear brake light but I needed to do some probing to figure out which ones the front brake switch was connected to. After that, wiring it in was an easy splicing job.
The last three things to mount and wire in from the electrical system were the battery, the main switch, and the 18V-12V power converter.
We tested the ignition key of the bike, for some reason this switch was broken so we decided to take a large E-stop button off a previous project to use as the main button
We decided to use Milwaukee M18 drill batteries because they have a 12Ah version of the battery and a lot of the tools I use are already Milwaukee tools - we got this adapter to mount it
Since the bike is designed to run on 12V, we needed a power converter to drop the battery voltage to the correct voltage
The bike already had some mounting points on the frame. We used two of the old battery mount points for the power converter and two for the battery holder. Both components were made of water jet steel and then painted. The battery mount has a small bend in it to increase the stiffness of the entire plate.
For the battery, we also soldered two large wires onto the terminals of the battery holder and then added epoxy to cover the solder joints to prevent shorting or other issues from rain or environmental conditions.
For the switch, we used a different mounting tab that already existed on the frame to just bolt the switch onto the frame with a single bolt. But we did make one other change, the large ring terminals in the switch were better suited to connecting the battery GROUND to the large ground wires coming off the frame. So instead of putting the switch on the 12V line, we used the switch to complete the circuit on the low-side so it connects the battery negative terminal to the frame ground.
Ok so the last steps were tank and seat mounting, painting, and other accessories.
The tank usually sits on some kind of circular rubber unit in the front and is held with a bolt in the back. The "C" shaped geometry of the front acts as a pivot and prevents the tank from popping out kind of like a slot. The bolt holds the back of the tank down and prevents it from moving towards the rear of the bike and popping out of the slot.
Ruth had both of these 3D printed, and we couldn't find the original parts. So we did two things.
horizontally drove a bolt through the frame that the front "C" of the tank could sit on
Drove a large bolt vertically into a tab in the back of the frame adjusting the position of the front "C" bolt until the tank sat snugly
The seat has a tab that sits under the fuel tank and then is usually bolted to the frame in the back. Instead of bolting the seat on we decided just to zip-tie it with some 1/2" wide zip-ties. We likely won't be taking the seat off often and it prevents us from having to drill into the frame more. The addition of the rear frame hoop actually acts as a "friction fit" for the seat holding it in, the zip ties are really just a safety measure to hold it down.
You can also see the exhausts were put back on in these photos.
I painted the front shocks the copper/gold color by wrapping everything around them in some newspaper I found in the recycling bin and then spraying them down. On the right side fork of the bike there are actually these old inspection stickers and the most recent is all the way from 1984. That seemed like a piece of history I couldn't cover up so I masked that part while painting and then clear coated it with a clear spray paint afterwards.
Took my first real ride on the bike in the back alley of the N51 solar car shop :) — she felt really good and makes a wonderful exhaust noise. After this I rode her back to my garage at home to work on since semester was starting and I didn't want to get in the way of the teams using the shop.
I got these handlebar protectors from revzilla which are classic cafe-style handlebar protectors. I left them silver for now but I might paint them the copper/gold in the future. I like the look of them, my friend Will suggested it.
I also took off the tank and painted with with Behr exterior spray paint (the light blue color). Once again paying tribute to the gulf orange and blue look from racing history.
Then I stuck a remove-before-flight tag someone gifted me on the fuel shutoff valve as a reminder that these old bikes have manual fuel valves I need to shut off when I cut the engine so it doesn't flood the carb.
Sticker time! The tank was looking a little bare without a logo so I wanted to add both a "Honda" logo as well as the name of the bike "Ruth" onto the tank. I went to Metropolis with my house-mate Cat and she helped me cut some fun stickers out on the vinyl cutter. We found this great dark-aqua colored vinyl which contrasted beautifully with Ruth's tank. We chose a script for the "Ruth" font and a more sporty font for the "Honda."
We used transfer paper to apply the stickers onto the bike and a squeegee to push out any wrinkles.
And that's it! She's ready to go. I took her out for a drive with my friend Maria, we went to a parking lot because Maria wanted to learn to ride and I took a few photos of the bike in the process. I think the photos came out well and I love the contrast of colors on the bike itself.
It was super fun restoring Ruth! I use her almost every day now to drive from university and back. There a few other things I want to explore in the future that I'll list here.
Cleaning the carb, I'm seeing a little bit of carbon fouling on the spark plugs and sometimes that indicates a rich air-fuel mixture, I replaced the spark plugs but I think cleaning the carb is the next step and then we can tune the idle speed as well, for now it runs OK though
Fixing the alternator to charge the battery, might need to design a board for this since the battery is now an 18V Lithium battery instead of a 12V lead acid, the alternator probably needs a full replacement
Electric start, the kickstart is OK during the summer when the engine is warm, but in the winter it does take a little bit to get the old girl running even with the choke on, fixing the electric start might be convenient
Overall this was a really fun process, I learned a lot since I'd never actually touched a gas engine before—so once again, thanks to all the people that helped me out. I hope to have many adventures with Ruth going forward, she's such a pleasure to ride. Maybe it's just the charm of the 70's getting to me, but the bike just brings me so much joy.
#motorcycles #restoration #caferacer