Honda CB750 Cafe Racer – Post 1 (8 December 2019):
The BMW K75C Café Racer was a great success but here is the latest build in the shop. It’s a 1981 CB750 F Super Sport. These bikes have a wealth of history. The first K series CB750 were made from 1969 to 1979 and were such a powerhouse of style and performance that the term ‘Superbike’ was first coined. The next generation of CB750 – the F series between 1979 and1982 built on that status. The engine improves on a SOHC to a DOHC, the suspension and geometry create a more exhilarating ride. The only downfall is the shape of tank making it harder to work with on custom builds.
To get this beauty I had to drive to the Eastern Coast of Victoria to a small town called Bairnsdale (about 3 hour drive from Melbourne). This bike also has some of its own personal history; with only about 13,000 kilometres (8,000 miles) it’s seen very little use over its 38 year old life. According to the previous owner, he inherited it from an old friend and had it sitting under a tarp for about 7 years before looking at it. He then started a project that he decided not to finish. I was however impressed with most of what he did to it. The previous owner was an engineering fabricator so the quality of work was good.
The engine was in a great condition with its low mileage and was checked before being cleaned and painted in a flat black etch primer. The exhaust headers (4 into 1) were purchased and the muffler was made in-house. I know it’s not shown in the photo here but he did such a good job that I’m likely to keep it. He also fitted it with some clip-ons and some aftermarket rear shocks (I’ll have to test ride these to see if they’re any good but they seem like good quality). The carbs were also cleaned and re-tuned, and the front end was re-sealed and oil, further lessening my workload.
Now the parts of the bike that I don’t like are primarily the seat, and the quality of the paintjob. The colour scheme is nice enough, but close up there are blemishes and runs. Also, other things that need to be done are the wiring and lighting. But more on that as we progress. Hope you all enjoy it.
Honda CB750 Cafe Racer – Post 2 (11 December 2019)
Here she is on a bench. I’ve decided to remove a number of things in order to get a closer look at it all. You may have already noticed something different about this CB750 F. The rear of the frame has been altered to remove the step-up at the shock. This’ll work perfectly with what I want to do for the seating area as it’ll allow for a straight line from front to rear. We’ll need to get a bit creative with the tank to make sure all the lines are there.
Honda CB750 Cafe Racer – Post 3 (15 December 2019)
So as we can see the first job after stripping down some components is to start working on the seat pan. This required putting the tank back on to see what lines to work with. The seat pan is made from 1mm mild steel and has been raised by 30mm to allow for electrics to be stored under the seat. The front of the seat pan will slide in to meet the start of the tank and should provide a smooth transition. The rear of the seat has a slight kick to it. A round bar with an integrated tail-light was purchased here and will be welded into place. The seat pan will follow these lines. What kind of seat are we going for here? I’m considering having two; a brat style seat and a separate seat and cowl that can be changed quickly for a café racer look. Why do this? Well I love the look of a CB 750 Café racer…but the future Wifey wants to jump on board too.
Honda CB750 Cafe Racer – Post 4 (22 December 2019)
The primary seat pan is almost done, I’ve gone ahead and folded up the café racer seat that will end short of the rear and allow for the rear cowl to go in place. The base of this seat is made from1.6mm aluminium. More cutting and folding will be needed for the brat style seat which follows the exact shape of the seat pan. We’ll also have to cut and fold up an electrical tray that sits underneath the frame. This will hold all the electrical components like the battery, starter solenoid relay, CDI Spark units and the motogadget M-unit Blue (Note that this version Honda CB 750 Cafe Racer will need a relay in the ignition circuit to work with the m-unit as they’re not directly compatible with CDI systems). The shape is coming along nicely. In a future post you’ll see all the pans, seats and electrical tray installed. Still some more work to do until then and with Christmas and New Years approaching the progress may be a bit slow.
Honda CB750 Cafe Racer – Post 5 (5 January 2020)
First blog post of the New Year. For those who are following this CB750 F project, Thank you, and I hope you had a great festive season. The team at JAX Garage sure did, but it’s time to get back into the swing of things. The most recent work revolved around the shape of the rear cowl. For this we used hard cardboard paper to get the approximate shape of the rear cowl. A raised mohawk was added similar to the profile of the tank. The next step here will be to cut out a sheet of 1mm steel using the template. Then it’s down to metal shaping to make sure it fits nice and snug and has the right lines.
I’ve also decided to add a couple photos of how the seat pan has actually been mounted to the frame of the bike. I wasn’t initially going to post about this but I see now that it could be useful to others who are looking at taking a similar approach. Thank you to supporters on Instagram for prompting me to do this.
The seat pan is attached to frame using fixed and mechanical attachments. At the front (closest to the tank) we have two aluminium cylindrical raisers and at the centre cross-member we have single large cylindrical raiser with a 3mm spreader plate attached. At the rear a 3mm mild steel bar was folded and welded to the frame. This is also where the rear hoop attached to the frame and acts as a reinforcement. The entire structure/assembly allows for the seatpan to be raised 30mm from the frame. Should be enough room to hold all electrical components.
Honda CB750 Cafe Racer – Post 6 (12 January 2020)
A short one. This week we had a chance to work on the rear cowl. The cardboard template was cut out and placed onto flat 1mm sheet mild steel. A 20mm extra overhang was given that would allow for easier shaping on the English wheel. The 20mm overhang was the cut and a lateral strip to match the profile of the seat pan. The removable cowl is really coming along. The photo below shows what the overall shape will look like before it’s all welded up. Next on the list is to clean up the welds and add the raised section.
Honda CB750 Cafe Racer – Post 7 (19 January 2020)
The removable rear cowl was cleaned up this week, cut to its final size and the sides and raised section welded/ tacked in place. The rear cowl is made from 1mm mild steel sheet and shaped, it’s therefore vulnerable to deformation due to heat by welding. That’s not to say you can’t weld it. But it would require welding a certain distance, stopping and then continuing once the steel has had a chance to cool down. Do this too quickly and risk the chance of warping. I spoke to a colleague that explained bronze welding to me. It’s a form of welding that joins two pieces of metal by melting sections of bronze over the join and allowing it to cool. With this kind of method the parent material doesn’t heat up to melting temperature and almost eliminates the chance for warping. The other advantage here was that the raised section edges needed to be filled. Instead now, the melted bronze fills most of this area reducing the amount of body filler required. Win-win situation here. It looks a little ugly at the moment but once it’s cleaned up and prepped for filler and undercoat, it’ll be just fine.
Honda CB750 Cafe Racer – Post 8 (3 February 2020)
It’s been an incredibly busy past couple of weeks and things feel like they’re finally starting to come together with the entire rear seat section ready for filler and then painting. The electrical tray, raised seatpan, brat style seat plate and the café racer seat plate and cowl have all been pretty much completed. There’s a mixture of mild steel and aluminium construction here. The raised seatpan was done this way to allow for the electrics to fit underneath the seating area, the electrical tray should therefore finish flush with the bottom of the frame and house all electrical components including the battery, although to fit the battery in the tray may need to be recessed, which will allow it to fit but also secure the battery in place as well. But more on this later down the track. Below I’ve attached a photo showing all the components. Note that not all of them will be installed at the same time. When the Brat seat is on the café racer seat and rear cowl will not be on.
And here is what the seat looks like when it’s on the frame. See the side view and the rear view.
To add to the progress, the rear hoop has been finally welded in place and the welds all cleaned up. Particularly around the suspension where this will be filled in with body filler to create a smooth frame transition.
And on a completely different section of the bike, here is a photo showing the newly manufactured replacement top triple clamp that we’re offering up for sale in our shop. It was designed and prototyped specifically for this model and incorporates smooth lines on the top to provide a clean view from the cockpit. Like our other triples, it also has two mounting holes underneath that are helicoiled. We’ll pick up a speedo bracket from here in the future.
Honda CB750 Cafe Racer – Post 9 (9 February 2020)
This week I stepped away from the rear cowl and seat and focused on the wheels. The front-end and rear wheel was removed, stripped and prepped for painting. The wheels were already in good condition and painted with etch primer. But I wasn’t a fan of the matte black finish and the silver ring. Now they’ve been prepped for a few coats of fresh paint.
Honda CB750 Cafe Racer – Post 10 (16 February 2020)
A quick one this week. Dom has done another excellent job with the paint work on the CB 750 wheels, just check out the photos below. The final finish was in gloss black. Now we’re just waiting on a classic set of tyres to finish them off. Other work this week involved dismantling the brake calipers. A new set of rubber seals is a must, so these have been ordered.
Honda CB750 Cafe Racer – Post 11 (23 February 2020)
Because this is a custom cafe racer we’re amping up the Honda CB 750 build by stripping down the rotors, measuring them and planning for some extensive modifications. The plan is to drill the existing rotors with a circular 3 hole pattern. The front and rear rotors will match with the same style. Why do this? We’re after a custom look but still want to keep some of the originality. Whilst some can dispute the performance aspects surrounding drilled, slotted and bare rotors, the main idea here isn’t necessarily to achieve a performance requirement. The drilled rotors should improve the wet braking performance – not that this build will be used in the wet if it can be avoided. It should also add some extra bite during cold braking. The vulnerability associated with drilled rotors such as cracking won’t be an issue here because there won’t be any serious track use to cause extreme fluctuations in temperature during repetitive braking. Setting that aside, here are a couple of photos showing the original rotors and the CAD drawing showing the drill pattern.
Honda CB750 Cafe Racer – Post 12 (1 March 2020)
Following on from last week I went ahead and drilled out the front and rear CB750 Rotors. I think they look great and should add that extra touch of uniqueness to the build. The effort that went into the drilled rotors was worth it. The process took almost three days and in the end I drilled out 144 holes between the three rotors. At roughly 2-3minutes a hole you can see how quickly this can add up. Here is a summary shot of the three rotors. If you check out the last three Instagram posts I’ve shared hyperlapse videos that show this process in some detail.
Honda CB750 Cafe Racer – Post 13 (8 March 2020)
The work on the CB750 revolved mainly around the frame and cowl. In particular, this was grinding, sanding filling, sanding, filling a it more…. and you get the point. The main aim here was to remove the lugs and brackets from the CB750 frame that weren’t going to be used after completion. By removing and patching these up with some sanding and filler work it’ll come up nice and smoke when it all gets painted up. So two photos here. 1. the rear of the frame making it all smooth, and 2. the cowl and making sure that all faces are equal and any lows are dealt with to provide a uniform state. This includes the bronze welded raised centre section which will now fade into the rest of the body work. The filling and sanding process takes a while and I used a mixture 80, 120, 320 grit papers to get the desired shape. When sanding I ensure to rub at 45 degree angles so that I’m cutting the filler away instead of just clogging the paper.
Honda CB750 Cafe Racer – Post 14 (15 March 2020)
This was a nice and productive week but I’ll keep this short and sweet. We received the Shinko E270 super classics. Here are the photos of the finished product. I also managed to document the installation of the rotors on the wheels which you can see on the previous Instagram post. One thing I wanted to stress is the importance of using lubricants such as antiseize or thread lockers during fastening. These are important for two reasons; 1. Ensuring that the fasteners aren’t loosened over time due to vibrations and 2. Adequately setting the torque – dry fasteners torque readings can be incorrect due to the friction to move the threads around. Saying that make sure to read the workshop manuals as these are your first point of reference.
Honda CB750 Cafe Racer – Post 15 (23 March 2020)
This week was a little slow going because of all the announcements regarding self isolation, quarantining and a potential lockdown with regard to COVID-19. It has forced to rearrange how we work a little, but now that we’ve sorted that out we can get back to work. The past few days we focused on stripping the CB750 F tank and removing the locking mechanism of the fuel cap. This was done because a) a new and better paint job will be applied to suit the style of the build. I haven’t decided on the colour just yet though. The removal of the locking mechanism is purely aesthetic. The original setup and contraption is quite unsightly and we’ll be doing something a little bit more unique here so stay tuned. In the mean time, check out the condition of the tank so far. A couple minor dents, but no filler anywhere. not bad for a 39 year old tank.
Honda CB750 Cafe Racer – Post 16 (29 March 2020)
I haven’t spoken yet about what electrical gear the CB750 build will receive but I think it’s time for it now as new parts are arriving. The first items in the shop are the flagship installation for any custom build, the Motogadget M.unit Blue, and the Motogadget Motoscope Pro. Other parts are still on their way. These include in a new starter solenoid from Revival Cycles, the Motogadget Breakout Box B to compliment the speedo installation, Motogadget M.Lock, Motogadget ignition signal sensor and an 8 Cell Antigravity lithium ion battery to power the whole set-up. When it comes to the electrical components make sure to always pick quality products. Whilst Motogadget are the go to for most things there are plenty of options out there,do your research and don’t rush with these things. In a future post I’ll share the wiring diagram for this setup so it’ll all come together nicely. Stay tuned.
Honda CB750 Cafe Racer – Post 17 (05 April 2020)
A big week. We’re at the stage now where we’re deciding on the total colour scheme. It’s always a safe option to go with a neutral colour with the frame and accessories and let the tank and cowl do the talking and that’s exactly what we’ll be doing here. So ultimately we’re going for a gloss black finish on the frame, wheels and so on. The engine will be matte black to provide some contrast with other components. The same idea goes with the forks, which are a satin black. The accent colour will be chrome/polished metallic finished around the bike like the suspension, rear brake reservoir, exhaust etc. The colour that hasn’t been decided just yet has been the fuel tank and seat cowl colour. I had a @fiorellogaluzzo, a follower and builder of his own CB750 reach out to help with the task. He took a previously posted side profile and photoshoped some general colours over the top. In my opinion the Red, Yellow and Grey stood out to me. I asked you all for your contribution and the results are in:
Red = 21
Yellow = 11
Grey = 8
So the red appears to be the stand out winner. Whilst I really liked all three colours the decision is between the Red and the Yellow. It’s also worth mentioning that this is just an example and doesn’t take into account the the finish of the paint job could be metallic, matte, gloss flat and so on. I’ll do some thinking and decide shortly. I’ll reveal the colour when it’s all painted up!
In terms of colour schemes, there’s no wrong or right answer and it’s all due to personal preference. I generally prefer a simple look. What I mean by that is keeping it to 3-4 colours. That is, one primary colour (Red, Yellow, or Grey in this case), a secondary colour (Black for the frame ) and accents (polish steel, aluminium, chrome etc.). There’s also a need to consider the seat and what colour leather and stitching to use but we’re some way from this decision. Another way to think about choosing colour schemes is to perhaps follow a theme.
In other news for the week. We’re starting to become more active on Facebook, so if you haven’t already started following please do so for additional updates and posts. The main social avenue will always be Insta and the Website / Email. Also, before I head off for this week, check out the fuel cap cover that Dom machined up out billet 6 Series Aluminium below. This is was done to add a unique feature of the bike.
Honda CB750 Cafe Racer – Post 18 (12 April 2020)
During the week we got the last set of the major electrical components. As mentioned earlier in this blog this includes the Antigravity 8 Cell battery to feed the electrical supply. It has the right amount of cold cranking amps (CCAs) to fire up the 4 cylinder engine and enough amp hours to keep the supply going. The other items that came in were the starter solenoid because the old one was shot, the motogadget breakout box to communicate with the Motoscope pro speedo, an ignition signal sensor so that the RPM signal is picked up digitally for the speedo, and the Motogadget M Lock (RFID Lock). You may wondering why I’ve purchased a RFID Lock when I’ll be using the Motogadget m.unit blue. I should have the ability to power the bike by touch or proximity of my smartphone. But If the app fails or I don’t have my phone I’ll need a back-up. Because I’ll be getting rid of the ignition barrel all together the back-up will be a proximity RFID scanner.
Now with all the components in I had the opportunity to quickly prop things up on the electrical tray before we remove the frame and get things painted. Check out the photo below. You’ll notice that everything is conveniently located directly underneath the seat and on the tray. The reg/rec will be located on a separate tray directly underneath the fuel tank. I’ve done a bench test on the original reg/rec and it appears good to go. I’ll still need to make sure that the reg/rec doesn’t over charge the battery during operation so I’ll need to check that when things are back together. When the wiring gets done, I’ll revisit this photo as well as make a wiring diagram that shows exactly how it’s wired.
Honda CB750 Cafe Racer – Post 19 (19 April 2020)
We hit a milestone this week with the build. The frame finally came off and revealed the engine all on its own. The frame is now off for some extra attention and treatment. Eventually this’ll mean going overall bumps and bruises, adding filler where needed, etch priming, undercoating, rubbing, painting and clearing the whole lot for optimal paint protection. With the frame we’ll be going with a gloss black finish. Then the tricky part will be putting it back on and over the engine without scratching the frame…. but we’ll talk about that when we get to it. For now, the build is literally in two. But rest assured, when the frame is finally painted it’ll come to the most exciting part of the build by putting everything back together.
Honda CB750 Cafe Racer – Post 20 (26 April 2020)
What does 20 Litres of White Vinegar give you? A clean tank – hopefully, and strange looks at the supermarket – When everyone else is hoarding toilet paper and pasta during the COVID-19 outbreak, here’s a man with a trolley full of white vinegar! Anyhow. This tank was in reasonable shape internally but after close to 40 years it’s got some surface rust in it. The reason for the vinegar is that I’ve done some reading on a gentle way of cleaning out minor rust from fuel tanks. The idea is to fill the tank with vinegar, put some agitator in like a chain and let it sit for about a week or so an shake it periodically to dislodge any rust. I’ve been doing that for a little while and I’ve got my fingers crossed it’ll work. But I won’t just rely on the vinegar. I’ve also purchased a chemical fuel tank cleaner and sealer solution (KBS Motorcycle Tank Sealer Kit). I’ll keep you posted with the end outcome once it’s all done. The insides should be nice and clean.
In other developments, we’ve completely stripped the frame and now have it ready for a coat of etch primer. This process involved two goes of chemical paint stripper, some pressure washing and then some elbow grease with the sander to remove off all the paint. The frame is nice and shiny now and free from the previous paint, which seemed to be acrylic and nowhere near durable enough. From here on in, the frame will get some extra touch-ups with filler to smooth out the rear, etch-primer, and then a couple coats of undercoat which will be rubbed down. Oh and excuse the K2 in the background… that’s a project for another time.
Honda CB750 Cafe Racer – Post 21 (03 May 2020)
Another productive week. I managed to get to cleaning the tank out of all the vinegar that I poured in a week earlier. In the end it was all sealed and ready to go. A final little adjustment with thank also happened, and that was cutting the bunny ears off just before the seam. Whilst I was working on that and getting other things ready, Dom managed to etch prime the frame and other components. They’re all ready for undercoating.
The tank cleaning process:
1. 20 L of white vinegar for one week. Slosh it around with a bit of chain periodically to dislodge any larger bits of rust. I was surprised at how well the vinegar worked and as I poured it out the clear vinegar turned orange. The tank was in pretty good condition to begin with so I was surprised about this, saying that, there are a lot of places within the tank that can’t be seen.
2. A couple litres of hot Vinegar to slosh around and empty out the remainder of the fluid. Here I had to act quick because of the potential for flash rusting.
3. KBS sealer kit in 3 steps:
i. Cleaning fluid and slosh around, letting it sit on all faces of the tank for periods at a time. This process took about 30-40minutes.
ii. De-rusting agent. Slosh around for 10-15 minutes. Clean out and allow tank to fully dry. Apparently this process can be done several times to try remove all the rust. But by the stage the tank was looking nice and clean. Probably due to the vinegar.
iii. Add sealant and slowly move around to all internal faces. Do this for 15-20minutes and remove any excess sealant.
Honda CB750 Cafe Racer – Post 22 (10 May 2020)
Very busy week this time around, and we put it to good use and got a lot done. What’s to cover, brake callipers, Tank and fuel cap, some work on the rear cowl and away from the bike – a custom wiring diagram! So without further ado,
- Brake callipers: All brake brakes were overhauled and their pistons and seals all replaced. Check out the photo below to see what the old piston looked like… Yeah, as you can see it really needed the overhaul. Having rusted brake pistons can lead to tearing the inner seal and ultimately brake failure! The job is quite a simple one, buy an overhaul kit, dismantle and clean the brake callipers, reinstate all seals, lubricate and reinstall. You can remove the old piston in two ways. One is messier than the other, the clean way is to remove it off the bike dismantle it all, clean, and apply air pressure to the hydraulic inlet covering all else. Warning: be sure to face the piston downward and into a rag or rubber, under high air pressure it can fly out and injure. The messy way involves doing it on the bike using the hydraulic brake pressure and removing the pads. Squeeze until it pops out… and clean up the mess. It’s also important to point out here that the CB750 F range had a transition in the front-end in 1981 and 1982. This change included a move from 35mm to 37mm forks, wider offset, and from two single piston callipers to two dual piston callipers. Be sure to check the part numbers before ordering your brake overhaul kit.
- Tank and rear cowl work: The tank was smoothed out and the rivet holes up top near the cap were filled in using bronze welding. The tank was let to cool down and filler was applied over the rest to get rid of any low spots. The finish should be nice and smooth when it’s all painted up and the custom fuel cover cap should come up really nice. Because we did some filler work here we also went back to the rear cowl. Dom smoothed this out really nicely and eventually got it ready for painting.
- Wiring diagram: Earlier on I spoke about some of the components we were using for the build. Here is where it all comes together. This wiring diagram takes the old CB750 wiring diagram fundamentals but incorporates the array of components that will be going on the bike. Also, you’ll notice that there is some overlap between colours. This is because I’ll be primarily making an entirely new wiring harness since that is the easiest and most simple approach. Whilst it doesn’t say so, all lighting will be LED. I was also fortunate to have this wiring diagram checked over by a local home builder of a CB750 who also happens to be an electrical engineer. Thanks @fiorellogalluzzo ! Check it out below, if you’re taking a similar approach feel free to use it as a guide under your own discretion.
Not bad for a week’s work I’d say!
Honda CB750 Cafe Racer – Post 23 (17 May 2020)
The week started off with us painting the frame with two coats of undercoat and some sanding back to smooth out all surfaces. In the end, the frame was finished with a 2 pack black and cleared with a couple coats of high gloss clear. The final result, is a magnificent deep black frame that will compliment the other black textures around the engine and other components. Check out the photos below!
We also did some important lathe work. The old footpegs had seen better days and lacked any sort of style and grace. So we machined new ones out of Aluminium that will go on to match the other polished and aluminium features and components that go on the bike. I’ve mentioned it before, but in terms of choosing colour schemes, we typically go for neutral colours with varing textures and shades for the frame and engine, a primary colour or two for the tank and cowl, and then an accent colour to tie it all together. In this build, the silver/polished finishes are the accent colours.
Honda CB750 Cafe Racer – Post 24 (24 May 2020)
A very significant week in the scheme of things. We managed to install the freshly painted frame over the engine and boy was it a happy time. To protect the frame during the installation and for any further work we used high quality painters tape to cover the inside and outside of the frame. This tape will only come off toward the final weeks of the build. Whilst most the fabrication work has been finished, it’s only there for protection. The last thing we need is a chip in the beautiful paintwork. Check out the side shot below. In the coming weeks, things will start to progress quick.
Honda CB750 Cafe Racer – Post 25 (31 May 2020)
The bike is getting closer to coming off the bench and rolling. We mounted the front-end on the bike. The fork height hasn’t been adjusted yet and whilst it may be a popular modification to shorten them we’ll be keeping them stock here. Shortening the forks definitely looks cool, but in terms of dampening performance you’ll be getting a much stiffer ride. The front-end install also gives a first look at the custom drilled rotors on the bike. Marked aesthetic improvement on the original. Check out the image below.
You’ll also note that the front-end includes our very own CB750 F Top Triple. The original was butchered by the previous owner, not that we would have used it if it was in good condition. The view from the cockpit and the front of the bike is now ultra clean. Here are a couple shots below.