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.
Honda CB750 Cafe Racer – Post 26 (7 June 2020)
One word sums up the week quite well. Progress. The rear swing-arm and wheel were mounted on the bike and she’s one step closer to being a rolling build. The side profile now shows the matching front and rear wheel-set and the drilled out rotors. We also couldn’t help ourselves and had to put the tank (currently painted in undercoat) on the bike to see how all the lines match up. Check out the photos below:
We also managed to fit up the custom made replacement foot pegs. The original weren’t the most flattering to say the least and the upgrade was well warranted. They’ve been quite popular since we first machined them up and we’ve decided that we’ll have them available for purchase in our shop. Check it out regularly or email us to pre-order them if they aren’t already up.
Honda CB750 Cafe Racer – Post 27 (14 June 2020)
This week saw a bit of everything. We painted the calipers – Gunmetal Grey, Although it also has a touch of blue in it that gives just another unique dimension. It was satin cleared for additional protection. All that thanks to our resident painter in chief Dom. The other works included shaping an aluminium fender although we haven’t finished it yet. It’ll probably be revised as we’ve decided to weld it in-place as opposed to fastening it to the fork cross-brace.
In other works. We also managed to prototype some additional components. The original fork caps were worse for wear and don’t align with the theme of the rest of the build. So we’ve gone ahead, designed and 3D printed a new set. These will also be available for sale at our shop if you’re in for a similar look.
Honda CB750 Cafe Racer – Post 28 (21 June 2020)
We decided to take a brake this week… or three, and fit them to the CB750 build. That is, the freshly painted and rebuilt brake callipers were fitted to the bike. The colour of the callipers really comes to light when on the bike. We’re confident the colour choice was the right one. The gunmetal grey has a tinge of blue and with the blacks and silvers on the the build it suits quite nicely. Now only to deliver with the paintjob of the tank and seat. Checkout the photo below.
In other works, we decided to purchase a new regulator / rectifier. The original was in good shape according to the bench test but online research and recommendations lead to the ultimate purchase. This is because a lithium battery is sensitive to over charging. Whilst the reg/rec may be in good condition, its the charging rate that we’re worried about. If it exceeds the batteries limits it’ll lead to premature damage and possibly fire. Something we definitely wanting to avoid. I’ll be doing a charging test later on when the bike is up and running so stay tuned. When it comes to picking a battery, ensure it’s compatible with the bike. Also, ensure the charging is up to scratch and suited to lithium batteries. Most older bikes are not so a new aftermarket reg/rec may be needed. If you’re looking for a regulator / rectifier for your build, it’s worth checking out Rick’s Motorsport Electrics. We’re not affiliated in any way, this is simply where we purchased ours.
Honda CB750 Cafe Racer – Post 29 (28 June 2020)
Some great progress with the build this week including a landmark moment.
The electrical tray was mounted on the CB750 for the final time, and is all done. The approach with the electrical tray is a unique one. That is, I haven’t seen it done on other custom motorcycles before. We lined the underside of the tray with automotive carpet/felt in order to dampen any road debris – Painting the underside in this region isn’t the most practical approach because after the first ride you’ll likely get marks in the paint work from debris flying up. This approach can be seen in the cars today as they try to reduce in-cabin noise, so why not take the approach with a motorcycle too. If you were paying close attention we did this on our BMW K75 Cafe Racer and it worked like a charm. Check out the photo below.
We also worked on a little dress-up kit specifically for the rear shocks on the build because they looked unfinished. Dome cap nuts won’t do the trick here so we custom machined the caps on the lathe. We won’t get into the specifics here yet because they’re not actually done. There’s still some polishing to be done but we ran out of time.
And the landmark moment? We cleaned the bench from nuts, bolts and all parts. The bike is finding it’s feet and will be coming off the bench early in the next week. Be sure to check out our Instagram throughout the week, we’ll be filming how we get our bikes on and off the benches. For now, check out the state of the cafe racer in making.
Honda CB750 Cafe Racer – Post 30 (05 July 2020)
A quick one this week. The Honda CB750 has made its way off the wooden bench top and rolled across the workshop floor for the first time in a while! We’ve had a few questions about how we get our builds on and off the benches so we took a time-lapse of the process. If you’re interested in seeing it, go to our facebook page or Instagram profile @jaxgarageau . In summary though, the workshop has a car hoist that we strap the frame to, lift and lower all bikes onto benches.
The bike is now on the red pump adjustable stand. It means it’s on the homestretch to being completed. Whilst it was on there we managed to get some photos of it in its current state (see below) before working on some electrical wiring.
With the wiring of the build it’s important to take your time. It can be a therapeutic process at times if done correctly (at least for me). If you’re following this blog readily, you will have noticed that we’ve made a custom wiring diagram that incorporates all the components in it. It’s now time to start wiring this thing up. We do it in stages because other things come up, but during each stage we make sure to highlight the circuits that have been completed or write a side note. I encourage everyone to take this approach because it helps with the understanding of the brains of the bike, and it makes the whole process of wiring a lot smoother. As you can see, we’re almost half way through our wiring, and the bike should be able to charge and and start-up.
Honda CB750 Cafe Racer – Post 31 (12 July 2020)
We focused our efforts on the suspension side of things with the CB750 Cafe Racer this week. For the rear it was related to making it look prettier and that involves finishing off the bolt/nut caps and putting them in place. The work was relatively straight forward and only required a bit of high school trigonometry to determine the depth of the chamfer in order to not cut through the bore. The end result is a much more uniform finish at the rear of the bike as the shock absorbers are tidied up.
The forks also received some love and affection. You will have noticed that on this build we’re not using our CB750 Fork Conversion Kit, but have instead decided to go with the original look. The forks were in too good of a shape to scrap them. We’ve designed a few things around this to make it more unique; our CB750 replacement top triple is now paired off with a set of custom made Fork Caps. These will be available for sale in our shop in a few weeks. We’ve decided to go with the Aluminium finish, but there will be choice of Aluminium, Satin Black and Matte Black.
Finally the ride weight was determined. We’ve decided that we will in-fact modify the springs by shortening them 40mm. This is so that the Cafe Racer / custom motorcycle look can really come through. The stance of the bike is considerably more aggressive as the rest of the body tilts down. What does this mean for the ride quality? Well, it’s something that we need test when the build is back up and running. According to online research and discussions with other builders out there the original front is rather soft. By shortening the springs by 40mm the ride will definitely get stiffer, the question is by how much. We’ll get back to this questions. Anyhow, here the current look with the tank, seat and cowl back in place.
Honda CB750 Cafe Racer – Post 32 (19 July 2020)
A quick one this week. Following on from last week in determining the ride height, we got around to making the cut. The bike now sits lower at the front and no more bull horns (forks sticking through the top triple excessively). The other work this week involved mounting the regulator rectifier. We’ve spoken about this in the past and will do an extensive review on it in the future. In particular, we’ll look at the difference between old and new regulator rectifiers and their compatibility with lithium ion batteries. We need the bike to be running for some test figures, but if you’re looking to view the discussion on this see the comments in the Instagram Post on this @jaxgarageau.
A pet hate of ours is wiring and brackets that are unsightly. Especially when it comes to the front of the bike because this is usually where most of the attention is on. The only things sticking out should be brake lines. So we always try find a spot on the rear wheel for the digital speedo sensor. Once again, if we can avoid using a bracket to mount it we will. In this case it works out perfectly to drill and tap the rear caliper bracket. It’s made out of Aluminium alloy and won’t interfere with signals and lines up directly with the metal rotor mounting plate. The sensor is one you’ll find in all digital motogadget speedos and the m-unit. It needs a special ultra-fine tap (M5x0.5mm). Check it out below:
Honda CB750 Cafe Racer – Post 33 (26 July 2020)
We had a slight change of plans this week. We were going to mount the fender that we shaped last week but decided against it. The fender was made out of aluminium and whilst we had plans of using a combination of nut inserts and fancy caps to make the mounting discreet, the best option is always the smooth one. So we got back onto the English wheel and shaped out a fender out of 1mm mild steel. This time around, we got it mounted by welding it to the fork cross brace. Nice and neat. Check it out below.
There’s a certain luxury to having shaping equipment. Anyone who is half serious about building one, two or more bikes could easily invest in some metal shaping gear like sand bags, planishing hammers, and English wheel and be on their way to shaping fenders and cowls just like we’ve done so far on this build.
Our fabrication work didn’t stop here. We also got onto the mounting frame for the headlamp. The headlamp we’re big fans of and are using on this build is the STEDI 7 Inch Carbon Black. Why this headlamp when there’s no convenient way of mounting it? Firstly it’s incredibly high quality for $190 AUD. In-fact, we couldn’t find a better headlamp that ticks all the boxes in terms of performance, cost and it being approved for use on public roads (ADR, UN ECE, DOT approvals). Secondly, because there is no housing required for mounting it’s nice and discreet and can be tucked into the handlebars a bit closer. Or in our case it’ll give more room for mounting other items like the speedo.
To make the mounting frame we bent 1mm flat strap to the 130mm diameter housing, tapped the rear auxiliary mounting holes (be sure to use grease to prevent swarf entering the housing or you’ll be there with a vacuum cleaner sucking it out), machined up some mounting lugs and spacers and there you have it. It’s ready to be welded together. For that, Dom will be TIG welding it in the next week or so.
In other works, we managed to get the exhaust system all together. The Delkavic exhaust looks the money! But we’ll need to see how loud it is before we get too excited. Noise limits are something to be mindful of particularly if you’re from somewhere that has particular rules on it. Most places do, but how strict the authorities on it is another question entirely. For this build we’re allowed to go up to 100dBa stationary noise at 50% RPM. Keep that figure in mind, we’ll be testing it in the future.
Honda CB750 Cafe Racer – Post 34 (2 August 2020)
We’re still fabricating parts for the CB750… and others’ CB750’s (We don’t usually write about our fabrication custom work/services for others in these build posts but felt it was appropriate since it was for the same make and model)
In summary, we ended up doing some work for a local who currently has a CB750 F project. He needed a fuel cap cover similar to the one that we have for this build so we got onto the lathe and made him a nice piece of aluminium to add to his fuel tank. Check it out below.
I think @fiorellogalluzzo will be quite happy with it when it’s finally on the completed build. How is the fuel cap cover fixed to the cap? We use high quality structural adhesive. In this case it was the Loctite 4080 FY range. Skeptical about adhesives, we were too, but not after watching them tow a 140 tonne locomotive with a glued coupling… very impressive!
In other works we managed to mount the STEDI 7 inch headlamp. The design for the mount is something a bit different. It required some tube bending, lathe work and welding. It serves as holding in place the headlamp as well as the motogadget motoscope pro dashboard. Very neat! the cockpit view should be very clean after this! We’re lucky to have Dom, our expert welder and fabricator on hand for such work!
We also got a new bit of bling for the build. That is, all the brake line banjo bolts were replaced with new stainless steel replacements. Note that they’re hard to come by because the thread pitch of 1.25mm are no longer commonly used. It’s a must for this custom motorcycle!
Honda CB750 Cafe Racer – Post 35 (9 August 2020)
The CB750 Custom Cafe Racer is really coming along nicely now. This week we were fortunate enough to take a good seat on it and dial in the positions of the controls and the motogadget instruments. This required placing the tank and seat pan back on of course just to see how everything tied together. Here are a couple shots of me on it. Yes I was making broom broom noises on the inside!
We also got to making the rear registration plate bracket. We deliberated on whether the bracket came from under the seat similar to the tail-tidy we used on our K75 Cafe Racer or whether to create a wrap-around from the swing-area. In the end we decided that we wanted the rear of the seat cowl and frame nice and clean and a single sided wrap-around bracket was used from the caliper bolts. This ensures the entire unit moves together. The bracket was made from 16mm mild steel tubing and a 5mm cross brace. The attachment points were also made from the 16mm tubing but turned on the lathe to bore out a larger opening. The end was welded in place allowing the caliper bolts to clamp the entire assembly together. We’ve left the end on the tubing open to attach some additional indicator lights here. For these we’ll be using the motogadget m.blaze pin indicators for a discrete finish.
Note that depending on where you’re from you may have more options in terms of mounting. A few people have already suggested that we could have gone with a side mounted registration plate set-up, but we decided against it because of regulatory reasons. In the state of Victoria, Australia we have a registration plate visibility requirement. The requirement means that the registration plate needs to be seen from 45 degrees when standing on either side of the bike. A side mounted set-up (whilst seen on many bikes on the road) is far from legal here.
Honda CB750 Cafe Racer – Post 36 (16 August 2020)
We’ve been spending a lot of time on the lathe this week. Most CB750 Cafe Racers are converted into single seaters. This allows for a more tucked in rear-end and a considerable weight reduction. We’ve made an attempt at getting the best of both worlds. A tucked in rear, weight reduction, style, but also allowing for a pillion passenger. We therefore decided to work on some replacement footpegs for the rear passenger that match the styling of the front riders position. You’ve seen some of this work before but here is a detailed breakdown:
- Measure twice, cut once: Do some measurements to ensure they’re comparable in style and look to the front pegs.
- Put it down on paper and don’t rely on your memory. Try doing a hand sketch of your design. Keep in mind the process of using the lathe and the mill and in which order you’ll do what.
- Get it in the lathe, clean it up to the diameter required, step it up for the knurled edge (in our case this was 30 degree angle). Be sure to leave yourself an additional bit of length so that you can move the peg from the lathe to mill and have room to work with. After this, it’s all about polishing the surface up by using a series of sand paper grits ranging from 240 to 1500. Then, finish off with some aluminium polish.
- Time for the knurled edge. There’s a special knurl tool which simply cuts into the material. Set it up just off centre and tighten. In our case we went a half turn to allow for a nice texture but without deforming the material. There’s a video of this on our IG acccount @jaxgarageau show the knurl tool doing its magic.
- Move the peg from the lathe to the mill. It’s time to mill out the longitudinal slots. For these we used a 6mm ball point drill bit. With regard to the depth, we went deep enough for a 3.5mm profile. Be sure to crank up the speed for clean cuts during the slotting.
- Time to part off the excessive length of the peg and face it. You’ll need a nice flat surface so this step is crucial. This is to ensure the drill bit doesn’t wander when we bore out a 9mm hole that will be tapped (10mm tap).
- Refer to your tap size chart. General metric is 9mm drill for a 10mm x1.25mm pitch tap. On the lathe you can bore it out and start your tap dead centre. Once you’ve gone in a few revolutions you can decouple the chuck and finish the thread off by hand whilst its in the lathe.
- Last step is to get some high tensile 10mm threaded rod (stainless will work too, but mild steel may bend). Cut the length required using an angle grinder and holding the rod in a vice. Be sure to leave nut or two on so that once you cut the thread you can retain the thread when the nut is pulled off. Otherwsie, you can get your die kit out and clean up the thread.
- You’re ready to mount it on the bike. Use a nyloc nut on the outer end and some medium strength thread locker on the peg side. Torque it up appropriately.
It requires some work, but the results can be quite good if you take your time. We understand that not everyone has access to a lathe and mill. For that we’ll be offering rider pegs and pillion pegs for the CB750 on our website shortly.
Honda CB750 Cafe Racer – Post 37 (23 August 2020)
We were back on the electrical wiring and components this week. You haven’t seen much work in terms of wiring because it’s been done in stages as the bike progresses and we’re moving on to different aspects of the build. This week however, we’ve made sure to take some key shots of what the electrical loom underneath the seat will look like (refer to the wiring diagram for finer details of what goes where). You’ll notice two things. All components are fixed on the tray and connections between components are bundled in a loom and wrapped with a self closing sheath. When it comes to sheathing it’s important to get a good quality product. It doesn’t necessarily have to be self closing (although it makes the process much more convenient), but what you’re looking for is anti-abrasive, heat resistant and fire retardant properties. The cheaper stuff generally won’t have any of these qualities. If you’re from Australia, you can visit Jaycar, but any good electrical or automotive store should stock something similar.
You want good, long lasting connections. This means having the tools and connectors for the job. Often overlooked are the connections to the m.unit. Each input and output connection is secured with a spring clamping mechanism that keeps the wiring in place. A simple way of hooking up the m.unit is to plug the ends of your electrical wiring directly in, whilst this will work, it’s not ideal. The gauge wiring used at each point is very light duty and over time each individual copper strand will break apart resulting in a looser and looser connection. To combat this we use a ferrule crimp that squashes all the wiring together in a tight bundle and provides a firm overcoat. The strands of a cable are always stronger together than they are apart.
In line with the electrical work we made a start on the connecting the switches and the rear indicators. For both we’re using motogadget gear. Specifically the m.switch mini and the m.blaze pin indicators. The indicators will be mounted at either end of the registration plate bracket. It’ll be connected with an aluminium insert that we threaded and slips in the inner diameter. it’ll be polished up nicely to match the features of the rest of the build.
The work for the m.switch mini involved cutting a slot in the handlebars. This allows ample room for both cables to thread through the handlebar. It also allows some adjustment side to side and up and down. Having the controls on one side will significantly reduce the clutter on the right side where the throttle is. It also means less work! The perfect thing about the m.switch mini is how well they integrate with each other to complete the look. We haven’t seen anything better out there on the market.
Honda CB750 Cafe Racer – Post 38 (30 August 2020)
This week we ran a competition over Instagram. It was in-line with the latest bit of work we did on the custom CB750. @davidmichaelmanchester won the competition by being the first person to guess the new part we were making – the billet aluminium grips. To make them (both sides – 22mm left and 25.4 right – for the throttle tube) we turned the aluminium stock on the lathe, bored out the holes for the handlebars and moved to the mill. Here we made six equidistant slots along the length of the grip and made a thumb step for extra comfort. Check them out below:
Note that the billet aluminium grips will be prototyped and made available on the website shop in 3 colour choices; aluminium, black, and black with aluminum slots. These will be available for 22mm handlebar configurations.
Honda CB750 Cafe Racer – Post 39 (7 September 2020)
We’ve been doing a lot of prototyping recently. Most of this has been around the the CB750 that we’re focusing our attention on. What does that involve for us? Well let’s take the billet footpegs that we machined earlier as an example. The measurements have already been noted, aluminium stock was turned on the lathe and cut on the mill. The pegs have already gone on this build and validated it so It’s made our life much easier, But we’re still in the habit of taking those dimensions, modelling the part and then 3D printing it so that we can assess it easily enough before it becomes manufactured in larger numbers. So one of the most important tools here is the 3D printer that we use. For a good accurate print it requires good calibration, it needs to be serviced regularly, and the right material choice is crucial.
You can see we had to take apart our 3D printer printing block above and replace the nozzle. After some time it’ll wear and produce less accurate prints due to the abrasion in the nozzle head. We print with PLA which is relatively gentle compared to other filaments so it should last a while. The other advantage over PLA when compared to ABS is that PLA does not shrink like ABS does. So when it comes to material type, not all are suitable for accurate dimensions. Filament quality is also important. A general rule of thumb with anything, if it’s cheap, it’s probably not good. In summary check out the print of the footpegs against the ones made in-house below:
Honda CB750 Cafe Racer – Post 40 (21 September 2020)
This week we tidied up the front-end by polishing up the stainless steel clip ons for the build. We then went ahead and made our final installation of all components. This included:
- Original modified brake and clutch levers.
- Domino fast response throttle lever.
- Our custom billet aluminium grips.
- Motogadget m. switch mini switch gear.
- Motogadget m.view bar-end mirrors.
- Motogadget m.blaze disc bar-end mirrors.
The custom billet grips give a nice contrast to the black motogadget components and tie in nicely with the aluminium finishes of the bike. You’ll also notice that the switch gear will all be located on one side. This will allow for left and right turn signal, horn and high beam, Kill and Start switches.
Note that if you want a similar set-up you can shop around by clicking the links above.
Honda CB750 Cafe Racer – Post 41 (28 September 2020)
This week we made some headway with the rest of the wiring on the CB750. You will have noticed that we’ve been tackling the wiring in stages and in between other works such as fabricating new components and so on. But this is arguably where it all comes together. That is, all the wiring was essentially finished and tested. What was involved in the process:
- Powering the circuit and pairing the Mototgadget m.unit blue.
- Testing and pairing motogadget m.lock.
- Calibrating the m.unit and all the lighting and functions on the motogadget m.unit. I’ll go through this in detail in the future. The features available or the m.unit are vast to say the least!
- Testing connections and power to the ignition system (as well ensuring it’s going to fire in the right order).
- Starter Motor Test.
We didn’t get the bike running throughout this process because we still need give it a change in oil and filters. But according to all tests there’s no reason for her not to fire. When it comes to old school Japanese bikes the systems are relatively simple.
You’ll also notice that during this testing we didn’t use the lithium Ion Battery. Well we did at the start, but without constant charging like a running bike they go flat pretty quickly so we used a car battery and a couple good quality leads. If you’re going to do it this way, make sure you don’t short anything out – you’ve been warned.
Here’s a happy snap of it all:
Honda CB750 Cafe Racer – Post 42 (4 October 2020)
A quick update for this week. It follows on from the last one where we conducted some testing on the CB750 and got it paired with the m.unit. We then decided to go ahead and finish off all the wiring. Since we’ve been doing it in stages it didn’t mean a lot of work, but it’s quite a significant step. It’s import to note here that all the wiring we have running around the bike is kept safe and tidy by wrapping it within a self closing wrap. It has anti-abrasive and fire resistant properties for extra safety. When it comes to wiring we’ve ensured that all pinch points are avoided and any sharp edges are cleared. If in the chance that the loom could be resting on a sharp edge we’ll be safe knowing that the wrap and in-built m.unit fuse protection will do it’s job.
Here’s a photo of the bike as it is. The next one will be very different. we’ll look at clearing away that blue tape.
Honda CB750 Cafe Racer – Post 43 (11 October 2020)
Here’s the new-look 1981 CB750 F Cafe Racer. As promised, we removed the the blue protective tape since we’ve finished all fabrication aspects of the build. The colour theme can now start to be appreciated without any distraction – the blue tape was quite polarising. We’ve gone for a subtle and elegant approach in the colour choice of the frame, engine and other components. Black is the main theme here, but with varying shades and finishes. The frame is gloss, the engine block is matte, the forks are satin, and there are hints of crinkle finish for some texture. Then we have the accent colours in the aluminium and stainless finishes. What’s left? Some colour to make the build pop – not revealing much in the colour choice for the tank and seat, but we have decided, we just need to get painting!
In other works, we finished all fabrication (famous last words) by completing the rear chain guard. We went for a unique approach here achieve a nifty and very lightweight looking guard by bending some 5mm mild steel rod. The main structure is made out of 3 pieces of rod. The first piece has 8 bends in it, all required a bit of back and forth between the bike, a bucket of water and the oxy torch. We finished it off with some perforated stainless steel plate. Good way to cap things off, especially on something that isn’t necessarily a feature of bike, but a requirement here in Australia.
We also decided to remove the cylinder head cover to measure the valve shim clearances. We’re at that stage now where we can look at dialing things in mechanically. We anticipate having the bike up and running any day now. The valve shim clearances were within (or very close to) factory spec. But this isn’t ideal with today’s modern unleaded fuel and the engines run hotter. We need to make a choice on either adjusting the shims and getting greater clearances to the factory manual, or adding a suitable fuel additive. They have their pros and cons, and we’ll be documenting what approach we go with in due course.
Honda CB750 Cafe Racer – Post 44 (18 October 2020)
We achieved a serious milestone with the CB750 Cafe Racer build. She breathes and fires, and after almost 18 months of not doing so, she idles rather well too! Now the tank and seat haven’t been painted yet but we have a temporary fuel supply set-up. It kind of looks like an ICU drip – Looks like even bikes need their fluids ha! How was it done? We had spare aluminium reservoir (originally used with a transmission oil cooler). It was cleaned and fitted with suitable hose and in-line filter. If doing something like this, be sure the reservoir is okay with fuels so they don’t melt and keep it away from any heat sources. The other more obvious aspect to it is to hang it up higher than the intake.
The bike ran incredibly well (Posted up a short video on Instagram @jaxgarageau) and had all cylinders firing. We haven’t dialed in the carbs yet, and we’ll be doing that just after we adjust the valves. But we needed to fire it up to do some fundamental tests in the meantime. This included the battery charging, oil pressure and ofcourse the m.unit.
Now, a bit about oil. When selected it, be sure that it’s suitable for your bike. These old bikes don’t need anything fancy, and if you decide to get a synthetic oil, be sure it doesn’t have energy conserving properties or you’ll find your clutch slipping. For this CB750, a SAE 10W40 standard motor oil is fine. Choose something that’s good quality thought and your bike will thank you for it, for many years/kilometers to come.
Honda CB750 Cafe Racer – Post 45 (25 October 2020)
There is a certain degree of black magic involved in tuning an old school motorcycle. This means extracting the most amount of performance possible, and keeping in mind the longevity and reliability of the engine. Luckily, bikes like CB750 have been around for many years, and riders, enthusiasts and tinkerers have had a long time to test and trial different approaches to ensure a sound and strong engine. The process from here on in will be as follows:
- Adjust valve clearances
- Check and adjust timing
- Sync and tune Carbs
First up on our list is the valve adjustments. We spoke of this a couple of weeks ago where we measured the clearances between cam lobes and the valve shims. We found them to be very close to factory specification. The manual for these calls for 0.08mm (+0.05mm, -0.02mm), which sets a range of 0.06mm (min) to 0.13mm (max). 40 years of experience by the Honda DOHC community suggests that the 0.06mm (min) is far too tight as the valve clearances tend to reduce over time. Burning of valves becomes a serious vulnerability, particularly as our engines now run hotter with unleaded fuels. The advice from the community (and apparently acknowledged by Honda some years later) is that clearances of 0.10mm (min) and 0.015mm(max) are the most suitable.
Adjusting the valve clearances is a relatively straightforward process. However, it is also a very time consuming process (very much unlike it’s older brother – the CB750 K Series with standard tappets). This is how we tackled it.
- Record all valve clearances between the valve shims and the camshaft lobes by using a feeler gauge. Be sure the tall end of the lobe is pointing away from the shim when conducting the measurement.
- Remove the valve shims in pairs and record their value in a table, then return them to their buckets. You’ll need a special tool to depress the buckets in pairs and pop out the shims (Important note: do not turn the engine over without the shims back in their buckets). The values printed on the shims indicate their height. So a value of 255 indicates 2.55mm. Sometimes the values can’t be seen so have a micrometer handy. So replacing a shims with a value of 260 to 255 gives you in increase of 0.05mm.
- Once recording all the clearances and the shim values it’s time to consult your table. You can swap shims between buckets to achieve the desired clearance and ensure you’re staying between 0.10mm (min) and 0.15mm (max). It’s likely that you’ll need to order in a few shims to get it close to perfect.
- Once you’ve ordered in the shims, go through the process of replacing or swapping the shims between buckets and ensure that when you’re doing this you do not turn the engine over without a shim in each of the buckets. It could take you a few revolutions of the engine to swap over all shims and have them replaced.
- Re-measure all the clearances between the shims and lobes just to be sure you’re within the desired range. Change or swap any shims if you fall out of your range. The word of advice when it comes to the target range is that you’re better off being slightly over the range than under the range. But of course, staying within the range will give you the best results.
For reference, here are a couple tables of the before and after values for our valve clearances:
Honda CB750 Cafe Racer – Post 46 (22 November 2020)
We had a little break from the CB750 build in the recent weeks but we’re back in full swing now! We’re busy improving our workshop and designing new parts to suit a variety of models. There are some minor bits and pieces of work that need doing on the CB750 F but it’s on the home stretch. Saying that, we’ve decided to make quite a drastic change in the powerplant – specifically, the carburetors. We were never truly happy with the old stock carbs and despite the previous owner claiming that he re-built them, they needed a proper tear-down, attention and an overhaul. The bike started and ran, with these carbs but leaked fuel due to stuck open floats and cylinder 1 was cold during idle. When looking inside, things appeared fouled up. So they had to come off.
We’ve always had one-eye on a set of RS34 Mikuni carbs from the start of the project and it was time to call it. So here they are folks!
Why Mikuni Carbs? Mikuni Corporation have been supplying OEM’s and aftermarket Carburetors since 1923. Throughout their 97 year history they’ve refined their design and prioritised a simplistic approach where they have fewer fuel passages and larger idle circuits. This makes them very forgiving, providing instant response and fuel delivery and allowing for easy tuning. They’re not quite set and forget, but they’re pretty close. In terms of performance, the RS34 carbs will allow the engine to breath and suck fuel in better. They claim an increase in performance by up to 25%. Whilst our custom CB750 cafe racer isn’t a dragster, it’ll be quite a nice feature to an already feature-packed build.
Next week, we’ll have these out of the box and looking pretty on the bike!
Honda CB750 Cafe Racer – Post 47 (29 November 2020)
As promised, we continued our work with the CB750 and installed our new Mikuni carburetors! We managed to spice things up a bit by polishing up a few brass fuel fittings and installing a set of 50mm velocity stacks to suit. Why velocity stacks? well, why not! They definitively look great and the bike will be used relatively sparingly, only to be enjoyed on warm weekends when the weather is fine. In terms of filtration, Velocity stacks are usually kept open but the risk of sucking in large debris is too scary so we’ll need to think of a discrete filter to insert, which won’t restrict too much airflow. For now though. Enjoy the sights.
For anyone looking to get a mirror finish with brass, aluminum or any other material, be sure to step it up with sand paper gently. We typically do a combination of wet and dry papers ranging from 120 grit all the way to 1500 and finishing off with a polishing paste and buff. The brass fittings have come up like a mirror, only problem is keeping the finger prints away!
We’ve still got a few steps involved here. When removing the carbs you’re left with two holes at the top of the engine that need to be sorted out. These are the crankcase breather and oil breather and usually circulate back through the airbox and into the engine. As you can see, we’ve got a pipe laying across already in order to tackle this problem. We’ll be sharing more as we continue, but the plan here will be to make a custom filter that will protect any debris from entering the passages. The build is moving along, and we’re at the crux of it now.
Honda CB750 Cafe Racer – Post 48 (6 December 2020)
This running blog first started life on the 8th December 2019. Can you believe it’s almost been an entire year since we’ve have this project going?… and what a year 2020 has been. Lots of positives to take away but also a lot of frustration and challenges that was brought up by the COVID-19 pandemic. We’re at the final stage of this build we promise!
This week we focused our attention to the two holes at the top of the CB750 engine that are left open when removing the airbox. These holes (oil and crankcase vents) usually recirculate back through the airbox and into the intake. It’s typically done to reduce emissions but results in hotter air and carbon deposits entering the combustion chamber. It’s one of the obvious reasons why the Mikuni carbs are able to produce more power because we now have fresh cold air being sucked in allowing for cleaner burn in the cylinders.
We’ve looked online for crankcase breathers and haven’t found anything to our liking. They’re simple at best, usually quite unsightly and wouldn’t fit with the other custom components already on the build. So we decided to fabricate a custom breather that joins the two at the top of the crankcase vent. The breather is a 4 part construction consisting of a main body, top cap, a threaded side fitting and a 100 micron filter. The top cap is clamped with 5 equidistant button head bolts. In short, this little filter took quite some time to make between the lathe, mill, hand polishing and lots of love and care. The end result is something we’re quite happy with it. It’s probably one of the final bits of custom work to finish this build off (aside from the paintwork… which is coming, I promise!). Check out the filter below.
Honda CB750 Cafe Racer – Post 49 (13 December 2020)
We try to keep auxiliary features on this build nice and discrete without dragging too much attention away from the main aspects of the CB750 Cafe Racer. This week we installed our freshly painted headlamp and rear registration plate brackets. The brackets are painted black to provide some depth and texture to the black colour scheme of the frame and engine.
The rear lighting and registration plate bracket came up better than expected. The satin clear gives a very OEM-looking finish. You may remember from earlier weeks that we turned and polished some aluminium spacers for the motogadget m.blaze pin indicators to mount on to. This adds another dimension to a “boring” bracket and definitely something we’ll continue to do in the future to spice things up. Check it out below:
We also managed to get back onto the carbs and think of a neat filter to insert and prevent large debris from being sucked into the combustion chambers. We used stainless steel mesh with a 100 micron perforations, cut them to size (a little larger than the diameter) and wedged them into velocity stacks, before clamping it all together. The mesh is concave in shape and definitely looks nice and neat. It will put our minds to ease when taking this bike out on the road. Whilst the mesh won’t prevent fine dust from entering into the engine, this bike will probably never see dirt roads or wet conditions if it can be avoided. If at some stage in the future we decide to change things, we can cut out a fine filter and press it against the stainless steel mesh for extra filtration. We’re yet to see what that means in terms of airflow and whether it’ll reduce the laminar flow created by the stacks though. Here are a couple photos below:
Honda CB750 Cafe Racer – Post 50 (22 December 2020)
What a way to mark the half century post (50) for our Honda Cafe Racer build. We got the bike started and running, and with very little work it was idling well on its own. The induction noise, pops and gurgling of the Mikuni carburetors still give me goosebumps. If you haven’t seen the video yet, go to our Instagram page @jaxgarageau and check it out.
We started dialing things in by adjusting the push-pull throttle cables and getting rid of any slack. About 1mm slack is desirable when you’re adjusting these cables. If you spend a little bit of time you’ll get it pretty close, and you will be thankful for the throttle response.
We pretty quickly got the bike idling and then moved onto the timing. The bikes are pretty reliable in terms of timing and chances are you won’t need to adjust the timing plate on the left hand side of the bike at all. But it’s worth getting a timing light on there and checking it out – in our case, we did actually adjust it just a touch to get it perfect. To do this you will need to connect the timing lead to the spark plug lead No.1 and get the bike going. Then check out the F hash marks (Firing) and try align the indicator so that it sits directly in-between the two marks. To move the plate you’ll need to loosen the 12 and 6 O’clock bolts and turn the plate clockwise – or anti-clockwise depending on whether you want to fire sooner, or later. If it needs adjusting, you’ll notice that there will be an improvement on the way your bike runs during idle. A point to make here is that you also want to make sure your idle speed is set to factory specs which is around 1100 rpm. Our Motoscope Pro digitial RPM readout wasn’t correct so we had to hook up the old analogue gauge and work from that.
What was wrong with the digital RPM readout? A little bit of trial and error, and help from our Instagram friend @Fiorellogalluzzo and we attributed the incorrect readout to two things:
- Magnetic interference of nearby lead (no.2)
- Inherently weak spark making it difficult for our Motogadget ignition signal sensor to pick up the spark.
To fix this we moved the the sensor closer to the coil and away from any potential other leads other than no.1 and turned it over so that it’s resting on its back face. Whilst the Motogadget instructions state that the lead needs to pass over the black side of the sensor we found it to be more reliable on the back.
In truth you shouldn’t need this sensor. When we initially made the wiring diagram this was included because the bike has a CDI ignition and the Motogadget digital gauges instruct that they don’t work with CDI ignitions. CDI stands for Capacitor Discharge Ignition, and a true CDI ignition means that the bike should continue to run if the battery is removed. This isn’t the case with this bike, making it suitable for the RPM gauge to be connected to the low voltage spark ignition wires. But always read your manual to make sure.
We also managed to fit up our custom rear brake reservoir. This fitted up nicely and runs parallel with the frame. At one stage we though it could do well with being tucked in behind the frame, but due to the work that went into the reservoir, it’s gloss finish, and popular demand we’ll be leaving it exposed. Check it out: