Another Honda CB400F cafe racer


Kickstart, shift on right, drum brakes and spokes
This is a bike build thread for a 1975 Honda CB400F Super Sport café racer with a series of catch-up images and an overview of the work I have done to date. This is my fourth CB400F crank up rebuild so I know this bike well but unfortunately I cannot keep this one for I need to sell it to finish my (overly documented) BSA Gold Star project. I am however building it as if I were keeping it and to my normal build standards. There are several bad cell phone images, so forgive some of the poor images.

It will be rebuilt with slight cosmetic and mechanical modifications and the goal is to have it look like a came from the factory with British stylings (black cylinder, Honda front drum brake, custom Manx single seat, Lucas tail light, clubman bars, Dunstall replica exhaust etc). I deliberately did not hack up the frame or make any modifications so it could be converted to stock should the new owner wish to do so. It will be very similar to two other CB400f’s I built and sold:


Honda CB400f’s were produced from 1975 to 1977 only as sleek, light and fast factory designed café racers. Café racer styled motorcycles did not sell very well in America in their day so in 1977 the handle bars were changed to be more upright and the foot controls more forward to appeal to American tastes. Only 5060 1977 CB400f’s were imported to North America. The CB400F has a cult following in Europe, Japan, Africa and America and most every part is available in NOS and/or aftermarket reproductions with a few notable exceptions. Also, Honda parts are much less expensive than the British parts I have been buying lately.


The Honda CB400F is a marvel: It handles remarkably well, stops with authority, snaps through the gears precisely--and motors along smartly. The bike feels all of a piece, as if a hundred separate design systems fell into perfect synchronization. Yet the attraction of the 408 transcends its obvious competence. Even a card-carrying Anglophile would agree that the CB400F has real character. If you can't respond to the CB400F's electrifying mechanical presence, you should immediately switch your sport to checkers."--Cycle World, March 1975.

My bike is a low, low number (one of the first 750 ever built) and low mileage 1975 CB400f bought for cheap as a untitled basket case, missing the seat, tank, side covers, brake pedal but basically a roller (sorry, no dramatic “before” image). I titled and registered the bike and then stripped, cleaned, prepped, primed and painted the frame and put it in storage while I worked on my BSA Gold Star. During that time picked up a tank, side covers, brake pedal and a few other missing bits along with new bearings, seals and gaskets, hardware, tires and more. My friends and I now have a proper workspace (the Winona Riders workshop) and a lift table so I am now finally building this bike. I hate to sell it, but I have a Gold Star to finish and ride so here we go:

Frame and Forks:

The frame, triple trees, stands and other black bits were cleaned, inspected, prepped and painted with a two-part catalyzed gloss black automotive paint. The swing arm was installed with original bushings (still good). I cleaned up the rear shocks and installed them.



The original fork tubes are in fantastic shape with no wear or rust anywhere. They are the best I have ever seen on an old Honda. I meticulously cleaned everything and sanded, polished and buffed the sliders. New OEM bottom bolts, copper washers, dust caps and forks seals were installed. They were filled with fresh fork oil and work perfectly.



Although not for everyone, I used a Honda CL/CB 360 front drum brake on this bike. Many people are quick to hate drum brakes yet have not made the time to learn how to set them up, adjust and maintain them correctly. To my eyes they not only look better on a café racer than disc brakes, they do in fact work very well. I simply hate dealing with brake fluid (its feel, smell as well as its paint removing abilities) though I have rebuilt more Honda master cylinders than I can remember. I am also rebuilding the original front wheel and disc brake system with a great rim and new spokes as an option for the future buyer.

The front drum was in good shape so I dissembled everything for cleaning and polishing. The rim was in poor condition so I bought a correct used 18”rim in very good condition, (Honda no longer sells 18” DID rims in the US, grrrrr) The old factory finished of the plate and hub was removed with aircraft paint stripper, wet sanded with 400 to 1500 grit sand papers and polished and buffed with black, brown, red and white compounds. I laced and trued the rims with new spokes and nipples, pressed in new bearings and added new tube, rim strip and a new 100/90/18 Dunlop D404’ tire. I had a local shop dynamically balance both wheels on their computer. I got the front wheel perfect but the rear needed a few weights.


stripping factory finish

Beautiful and functional.

The rear hub was an absolute nightmare and took a lot of time and energy and I considered buying another used one, but in the end I tackled it. Good thing I like a challenge. It was covered in rock hard grease, oxidation and the brake shoes were frozen to the drum and the sprocket was not coming off until the BFH (big fuckin’ hammer) appeared.

The OEM chain cover over the sprocket was removed by drilling out the rivets and though I repainted it, decided not to use it. After degreasing, scrubbing and media blasting, I painted the hub and cover with VHT silver paint and heat cured the parts in my oven. New bearings were pressed in, the rim polished, new spokes and nipples laced and trued the rims to .005” lateral and radial tolerence. The hardware was zinc plated, new brake shoes and springs and a new sprocket was installed. Both hubs were spun on the stand and I used varying degrees of sandpaper to remove the crud, rust and bring inner drum lining closer to truth.



Media blasted






Ahhhh, much better

To determine the correct offset of the rear hub I centered the front rim between the forks, laced and trued it. Next I ran parallel straight edges from the trued front rim to the loosely laced rear rim to determine the correct position relative and in line to the front. then I measured the offset on both sides and then trued the rim in my stand. The centers of both rims are perfectly aligned.

Centered front rim
front to..
IMAG0868.jpg determine alignment and rear rim offset


with the correct offset the rear rim was trued on the stand

I mounted new Dunlop D404's (100/90/18 front and 110/90/18 rear), tubes and rim strips and got to one of the best moments of any build; ROLLING CHASSIS!

Motor rebuild coming next…
Motor Rebuild

Here is a quick overview of the motor rebuild. Nothing fancy or tricky, but I took my time to do it right following the factory service manual and a Haynes manual. Cleanliness was important as well as measuring everything, taking notes and using plenty of engine assembly lube. Any part that questionable or bad was replaced. The engine cases were cleaned, degreased, prepared, painted and heat-treated with Dupli-Color VHT aluminum 1615 paint. Three sessions of oven curing 150, 200 and 300 degrees F hardens the paint and make it oil and gas resistant.


Next was a meticulous crank up rebuild, ensuring all components are to factory specifications. Anything that was out of spec or questionable was replaced with Honda OEM parts. All new seals and gaskets were used. The rotor is difficult to remove without the proper Honda service tools (which I purchased but was given the wrong size). I opted to borrow a heavy puller from an O’Reilly’s auto store to remove it (along with PB blast and heat it came off easily) New seals were installed on each end of the crankshaft.


All the crankshaft journals were measured, the bearings checked with Plasticgauge and fortunately everything was well within factory specification confirming this is a low mileage Midwest bike that saw little abuse or use. The cam chain guides show little to no wear and everything inside the motor looked great, no drama, all good.



The cylinder, pistons and rings were cleaned and checked, all good.



New main shaft bearings and snap rings were installed, the transmission, cam chain guides were inspected and then I buttoned up the lower end sealing each half with Yamabond. All good.



The cylinder was soda blasted and painted (non-stock) gloss black with VHT paint and heat cured in three cycles.


The cylinder head looked awful and took several hours to degrease, dissemble, clean, soda blast, prepare and painted high temp black and heat cured. One valve head was corroded so I replaced it with another I had in storage. All the valve stems, springs and goods were to factory specification so the were cleaned and the valves ground in and installed.



The motor was placed in the frame by myself (easy and lighter than a CB750 motor) I have done many time before and use pipe insulators to protect the frame.)

The oil pump was dissembled, inspected and cleaned. All good. put in the starter, new sprocket and chain and installed the left hand cover. All the threaded holes on the engine cases were chased with a greased tap and I used a stainless steel allen bolt kit for all the covers with anti-sieze lubricant on the threads.



The gear change assembly was cleaned and installed. Clutch was in good shape and plates and springs have plenty of life left in them so they were cleaned and installed. I made a service tool to torque the clutch hub nut. An old socket cut to fit the four slots on the nut, not pretty but effective. I polished the clutch inspection cover and roughed in the clutch cable so it functions, but I will shorten the cable later this week.



New chain and sprockets were also installed as set. I did drop the front sprocket to a 16 tooth based on research and others’ recommendations. The 6-speed transmaission has a short first gear so this may help a bit.


The OEM 4 into 1 exhaust was in good shape, not perfect, but good. This piece of plumbing with its sexy, swoopy and curvy bends is one of the most beautiful headers ever. New Old Stock (NOS) ones are selling for $1200 and up on Ebay. I see David Silver Spares in the UK are selling very nice reproductions but I am sticking with this one and after cleaning and polishing it it looks pretty good. Also I soda blasted the exhaust collars and they look great. I bought a replica Dunstall muffler and with some extra baffling. The Emgo Dunstalls work and sound better when you replace the tissue paper thick fiberglass that comes with them with better baffling. I run two Dunstalls on my Triton with the same set up.


original baffling

Moose baffling

I was inspired by this video:

I spent a lot of time, money and energy tracking down and buying a lot of the little bits that were missing as well re-zincing most of the hardware. The motor, exhaust, rearsets, brake pedal, kickstarter etc were finished and installed last night and I set the valve tappet clearances so I can now add oil, do compression and leak down tests and then start work on the carbs, electrical, tins and seat. Stay tuned…
gee you have been a busy boy ;) lucky new owner to have you rebuil this, good job.....
Yup......signed up for sure.

Great work Swan - the future owner should be very happy with a "new" 400F.
Looks like a nice stocker rising from the grave! Love these 400's. Great platform to work with.
Thanks all! I was not going to do a build thread for this bike at first, but I changed my mind and will keep the updates and images coming.

Last night I added oil and kicked it over to get the oil into the internals but did not test compression yet. No leaks, drips or errors.

Started on the electrical, bought and charged a new battery and dug my way through three wiring harnesses that I picked up over the last few years.

Two are hacked, spliced, duct tape, wrong connectors and wrong color extension wires-total amateur hour and a pile of useless spaghetti.



The third was dirty but unmolested with the correct part number so I cleaned it up. The fuse holder is broken but usable.

I have three left hand controls but did not think any of them are for this bike. I hit the service manual, wiring diagrams and multi-meter to sort it out and ended up repairing a bad HI/LOW switch on one control and it is the correct one. I need to take it apart, drill a hole for the wires on the side to fit the clubman bars and paint it to match my new OEM right hand control. The old right side controls ALWAYS have a broken or fragile starting button, so it is best to start with a new one. Of course the left hand control is no longer available from Honda in the US, but they are still available in the UK and EU.



I have a busy couple of days at work and socially but will work more on this bike later this week. I want to get this thing running within two weeks. Stay tuned...
I was watching Swan working on his seat all afternoon today. This is going to be a sexy bike when it's done.
Thanks all, a quick update: The electrical is 98% sorted, tested and installed and my left hand control is painted, assembled, tested and installed. It looks good and works great. I found a good fuse holder in a box of spare parts.

I am greatly inspired by Oldog's thread on making a fiberglass seat mold and producing a seat pan and decided to buy the materials to do this. One, so I could learn the process and two, I want to produce seats for my CB750, KZ400 and possible other projects for guys in our shop. This will be a Manx style seat with black marine vinyl covering the entire pan with red piping to match the tank. I took detailed measurements of my tank, frame and rear fender and made a cardboard template. It is important to me that it uses the stock locking mechanism and hinges and I want it to look like it could have come from the factory.

Next, I glued with a hot glue gun pieces of scrap foam insulation I had been saving and marked out the general shape and form. The rough form was cut with a hacksaw blade and hand saws. Next,I used rasps and rough sandpaper to get to the final form. More sanding with finer grit sandpaper and then coated the plug with lightweight body filler.


With more rasp and sandpaper work, additional coats of filler, I am nearing the final form of the plug and plan to finish filling and sanding it tonight so I can paint it with a two part epoxy primer and then create a mold from it

From this plug I will make a mold from which the seat will be cast using black gel coat, epoxy resin and airplane grade carbon fiber I friend gave to me. It will take several days for the mold and cast pan to be made and cure so I plan to start on the carbs during the drying process.

They are complete, and are not in terrible condition but I plan to spend many hours inspecting, cleaning and rebuilding them with new carb kits. Each step is one closer to a finished bike.
COMPLETELY BEAUTIFUL BIKE! You sir are an artist! I can't wait for the finished bike!!! The detail you put into every little nut and bolt...congratulations!

Updates: Carbs are done and the seat mold complete

I made time to finish cleaning and rebuilding the carbs. Overall, I spent 6 hours dissembling, cleaning, rebuilding and setting them up and I really need to be in relaxed frame of mind to do this detailed work. I soda blasted the bodies and the interior of the bowls. The exterior of the bowls and caps were polished on the buffer.

We have all been here before, years of sitting, dirty exterior and varnished gasoline in the bowls-yuck:


New rebuild kits, #80 main jets and lowered the needle clip one notch (raising the needle). I used the same set up on other CB400f's and this will be my baseline for tuning with K&N pod filters, stock header and Dunstall replical muffler. Plug chops and a carb synchronizer will be used to determine the final carb set up.

This was one of the best set of carbs I have worked on. Dirty, yes, but no corrosion of metal, zinc plating is in great shape, nothing missing. Someone had been in the lower portion before, but not the top parts. The slides are prisitne:

The floats had undersized pins and drill bits holding them loosely in place and they were set to the wrong height. I threw them out, bought the correct diameter rod stock from a model/hobby store, cut to fit and installed. They work correctly and I set the float heights to 21mm.

The only drama was on the carb number 4 float bowl screw. It was very tight even after soaking in PB blaster. I was literally walking over to grab a propane torch to heat it and I made the mistake of trying to turn it once more and it snapped off. F#$%!

The broken piece came out easily with a screw extractor and I replaced it with a spare screw from one of my shop mates, thanks Andrew.
The carbs done and installed on the bike. I will shorten the stock throttle cables and install them this week.



Since I am making a mold from which to cast a seat, there is much more work and several more steps involved then simply casting a seat off a plug. Again, Oldog's thread was of great help and I am bodging my way through this to learn the process and made a few mistakes which I corrected and learned from so my next attempt will be better. I am experienced with fiberglass and resins but not gel coats.

The sanded plug was sprayed with multiple coats of two part automotive sealer/primer and wet sanded with 220 to 1000 grit sandpapers. Next three coats of Partall Wax was buffed on and then topped with a PVA mold release film. The beer is optional.

Next, several layers of black tool gel were applied with a brush. I do not have a dedicated spray gun for gel coats (yet). Things went bad on the second coat and there was some wrinkling which could be attributed to an inaccurate mixture of the gel and catalyst or most likely too thin of a coat due to brushing, not spraying. From the Fibre Glast website:
"A coating less than five mils thick may wrinkle, especially when brush marks are present. Check the thickness using a gel coat thickness gauge. The preferred thickness is .010" to .020". Live and learn....

After the tooling gel set, layers of fine weave fiberglass and epoxy were applied followed by two layers of a heavier fiberglass mat. The mat may have been too thick, was difficult to work with, leaving me with some air bubbles on the final coat (whitish areas). The mold ended up being very solid and will work well, but just looks ugly. For the next mold I will start with fine veil, regular weave and then a single layer of lighter weight mat fiberglass.

The plug was removed and the inside of the mold was washed with soap and water to remove the release film, The wrinkling in the tooling gel left valleys which will show up on the seat if cast as in, so to correct this I filled the valleys with a few rounds of light weight body filler, sanding and then sprayed the same catalyzed primer sealer I used on the exterior of the plug. Then the mold was wet sanded up to 1000 grit, waxed and sprayed with release film. There are still a few minor imperfections in the surface of the mold. I can live with them since the final seat pan will be upholstered. The flaws are more obvious on the flange of the mold, but that part will be trimmed off.



Tonight I will brush several layers of tooling gel into the mold and plan to lay some fiberglass and carbon fiber tomorrow, have a seat pan by Tuesday and start sewing a cover on Wednesday. Stay tuned...
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