1974 Honda CB750 Cafe Build

swan

Kickstart, shift on right, drum brakes and spokes
DTT BOTM WINNER
Intro
I am documenting a cafe rebuild of a 1974 Honda CB750 K4. Let’s call it a chopper rescue project. I have built many Hondas and British café bikes and frequent this and the SOHC forum often but have never posted a bike project from beginning to end until now, so here goes…

I will document the major portions of the build as reference for others doing the same, post problems encountered with my solutions and emphasize the non-stock custom work. Many areas of CB750 restorations are well documented on this forum need not be repeated (carb and tank cleaning, frozen brake caliper, etc).

History
Two years ago I bought a K4 and a K3 CB750 from dude out in the countryside for cheap. I had other project bikes in progress but the price was too good to pass up, so I bought them and stored the until this week.. The K4 turned over and had compression while the K3 was frozen. I spent an afternoon cleaning the carbs, tank, petcock, installing new battery, flushing the old oil and put the 4-4 exhaust from the K4 and fired her up. Tweaked it a bit and it idled and rode well, but the front brake caliper was frozen so I only rode a few miles on empty back roads to assess its condition. Solid motor, clean functional carbs, transmission crisp and smooth, crap brakes and tires and ugly as hell. A perfect candidate for a café rebuild. For the Honda purists, I am not destroying anything special, it is a Honda K4, not a Vincent, and there are thousands of these rotting away in barns, garages and backyards.

Life happened, several other bikes completed and sold, fell in love with a Norton, so I am finally making to the time to tear into this project. I have bought a mountain of new Honda OEM and aftermarket parts waiting for this bike. New rims, tires, spokes, all new cables, Fast from the Past rearsets, battery, pod filters, larger main jets etc.

Personal
I am a British bike junkie and build Honda cafes as my methadone and financial source to support my British habit. Like most everyone on this forum, I enjoy wrenching, building, restoring bikes and the pride and self-satisfaction of making something old beautiful again. It is my passion and hobby, but not my career. My day job is in the museum field and I am a trained archaeological conservator and work with high end art and priceless objects centuries and millenia old, so 30-50 year bikes are relatively easy and simple to work on. Free time is scarce for me and is spent either riding or restoring bikes to keep me sane and out of trouble. Cycle therapy.

Goals
My goal for this bike is to build a cafe racer in the true sense and spirit of the term: stripped down and fast with good handling to mimic the British track racing bikes of the 1950’s and 60’s. Appearance, though important, is secondary to function. There is more to a café racer than a bad black paint job, rearsets and an ugly seat on an ill running bike. I do crank up rebuilds on all my motors, complete rebuilds on my wheels (new bearings, spokes, rims and tires), meticulous electrical and carb work and work methodically, without shortcuts. The 74 K4 will be based heavily on two of my previous CB400F café builds; Honda Milano red tank, Manx seat, plain black side covers, black cylinder, clubmans, rearsets, 4 into 1 exhaust, rebuilt wheels etc. A strong and powerful girl in a sexy red dress. The K3 will have a strong Norton Manx and Triton influence (black hubs, front drum brake, black fenders, Manx seat, rearsets, clip-ons 5 gallon Manx tank, Dunstall and John Tickle style goodies etc). One of these two will have a GT550 4LS shoe front brake drum just like my Triton.
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My first CB400f cafe build
Recent CB400f cafe
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CB750 K4 as purchased in all its 1970’s chopperesque glory. Ugly, but got her running within an hour. A solid bike, but since it has been sitting for years I am going to build it from the crank up with all new gaskets, seals and replace the bearings as needed. Repaint cases, polish covers and rebuild carbs, paint frame, rebuild wheels etc, here we go…..
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Finally, made the time to start this one. 6 uninterupted hours of bike time on a Friday and 8 hours on a Saturday-heaven! Stripped her to the frame, pulled the engine and pounded knee indents in the tank, first coats of filler and sanding.
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I cleaned the exterior of the motor, pulled the carbs, soaked the cover screws in PB Blaster overnight and removed them with an impact driver. All but two screws came off easily. One screw on the breather cover got strippied and one on the stator was drilled and removed with a reverse easy out tool in a hand drill.
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The stator and clutch covers were removed along with the carbs, clutch plates and basket, starter, oil pan and filters to lighten the motor before pulling it out of the frame. Two lifts and I got the beast out of the frame and on to a milk crate. It is still weighs more than I do.
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Everything was cleaned, photographed, bagged and labeled. The frame and swing arm was an oily mess, but all that oil kept the rust at bay. Spiders were evicted.
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Proper use of a self-service carwash....
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Sump oil filter…. This is why I always strip my bikes down to the crank. You never know what has happened to your bike with the previous owners.
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I have been waiting two years cut the rear hub out of the god awful, ugly 16’ Harley rim and fat tire. Why people insist on hobbling their machines with fat rear tires is beyond me. The hub will be highly polished, drilled with a few large holes with screens for ventilation, but will not have shotgun blast holes a la Carpy. I have a brand spanking new 18” DID rim, new spokes and Dunlop D404 waiting to surround the hub.

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I picked up two Suzuki GT550 4LS front drum rakes recently. One, I bought a $200 parts bike to get it and the other I literally stole from someone on Craigslist who had no idea it was worth $300-400 unrestored (To thwart hate mail and possible theft charges I will not reveal the price). I collected all the necessary parts to install dual drilled front discs but I may go with the GT 4ls drum on this one.

The K4 tank was exceptionally clean and had one small dent, so I filled it, primered and painted it black. It is not pictured and I will save or sell it. For this project I used the tank from the K3. It was clean on the inside, but a Bondo queen on the outside and the tank badge holders were filled in. It was ugly and I had no problem smacking it with a hammer. I created a pattern outlining my knees, traced it on to the tank and pounded away with a rubber and plastic headed mallet. No problems, easy to do and both indents are symmetrical. The indents were filled with body filler and sanded twice. I layed down one guide coat of primer and sanded it to determine the high and low spots of the tank. I filled the lowspots, sanded again and it now has another guide coat. On more round of sanding and spot filling and then on to final prime, paint and clear.

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I am busy this week and a have big pile of junk waiting for me this weekend. Frame to paint, tank to sand, prime, paint, clear and polish, motor to break down, rebuild, paint, polish...

Cannot wait, stay tuned…
 
i love the self-service carwash...looks like you did great work on the 400's can't wait to watch your progress on the 750
 
Thanks, I have been waiting a long time to dig into this bike and want to do it it right.

Stay tuned...
 
Awesome! I just read your method on body work for the tank. i've been having trouble getting mine to shape right. I'm also having trouble filling the badge mounts. I always get outlines of the bondo, so either I'm not feather edging enough or I'm feather edging a lot.
 
Busy week, out of town with little time to touch the project. I managed to sand and polish the fork lowers, front hub, primary covers and dissembled rear hub as well as picked up new bearings front and rear.

You know the drill: paint stripper, clean, 400, 600, 800, 1000, 1500 grit sandpaper wet and dry and polish with black, brown and white polishing compound with lacquer thinner clean between all.

I will have a full day off on Thursday dedicated to working on bikes and have another pile of new parts ready to go.
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It was a beautiful weekend and I spent most of it working on bikes. The Norton got new exhaust headers and I put 200 miles of curving, empty backroads on her.

Several hours were spent cleaning, preparing, sanding and blasting the CB750 frame, swing arm, stands and trees. I spray primed everything with a two part catalyzed primer and painted with single-stage gloss black and flat black for yokes. Everything was wet sanded with 1500 grit to knock off the orange peel and followed by hand and machine poishing with 3M rubbing compound, swirl remover and final polish. I love my Dewalt 849 polisher! Everything looks great and it is a shame though most of the frame will be covered.
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I laced up the polished front hub with new spokes into a new DID rim, new bearings, trued it, and wrapped it in new rimstrip, tube and new Dunlop 100/90/19 D404 tire. Looks like it is doing 100 mph when standing still. Truing wheels takes time and patience but is one of favorite parts of any bike build. Something very zen about getting the axial and radial rotation perfect. Here is a very easy to follow tutorial on trueing from Dan Jones on SOHC forum: http://forums.sohc4.net/index.php?topic=368.0
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The rear hub was cleaned, stripped and I started to sand it. It takes ages to polish these hubs to perfection.
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Dissembled, cleaned, polished the front forks and rebuilt with new seals. Still need to drill and paint the front rotor and then the front end will go together.
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One more round of guide coat sanding and spot filling on the tank was done and I repaired the side covers with MEK and ABS plastic. I found some Legos at a rummage sale, mixed them with MEK to create a glue to fix and seal the cracks on the covers. It works and I read about this method here http://forums.sohc4.net/index.php?topic=49736.0

I have a busy work week ahead with limited free time but am looking forward to building the rolling chassis, finishing the tank and covers. Stay tuned...
 
Well, time to dust off this project and get started again. Cold weather is here, snow is coming and time to work in my cozy shop all winter. I will have several restored bikes this spring. With this CB750K4, I want to put her on a diet, shed much of the unneccessary stock components, add a British cafe racer elements of style and produce a fast, well-handling and reliable motorcycle that looks like it could have come from the factory.

For the first time ever, I had problem titling this non-titled bike in Minnesota. I have successfully obtained titles for 7 other bikes with Bills of Sales and sellers' statements but since this bike came from Wisconsin I had problems titling in it Minnesota. I will come up with an alternative method to get it titled by this spring (title service, forum member titling in another state and "selling" the bike back to me, etc) While this project has been in storage (3 years) I have moved house, rented a proper workspace (with a lift, tools and refrigerator full of beer, etc) bought, restored and sold or kept several other motorcycles (several CB400f's, 1966 Triumph Bonneville, 1959 BSA A10, 1974 Norton Commando, a few more CB750 parts bikes and my beloved 1962 BSA Gold Star restoration). I have nearly all the parts I need, the bike frame has been painted gloss black, wheel hubs painted, new bearings pressed in, trued spokes, rims, new tires etc. She is a rolling chassis and time to get back to work.

I lugged the motor over to the Winona Riders' workshop yesterday so I could break it down to the crankshaft, access its condition, clean, paint and heat cure the engine cases, cylinder, head and covers, new gaskets, seal and anything else it needs to be new again. I did run and ride this bike when I first bought it and it had good, even compression in all four cylinders and rode well. Here we go:
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Several hundred pounds of grease, oil, dirt and anodized alloy-yuck.

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Upper valve train looks really good and clearances were all correct.

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No problems removing the valve cover or cylinder head other than one marred screw from my impact driver. The pistons were evenly carbon coated and the bores look good, no damage.

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All four cylinders are even and well within factory specified standard wear. No trauma or drama, confirming what I suspected; this is a common Midwest bike that suffered lack of use rather than abuse. Hopefully when I dig into the lower end tonight there are no problems. Regardless, I will strip it to the crank, measure all the tolerances, rebuild with new gaskets and seals and fix or replace anything bad. Stay tuned...
 
LOVE your work and your bikes man! Keep us entertained with this build please!!!
 
Thanks all!

One step forward, several steps back....

I dug into the valves, springs and guides. So far, so good. The valves and seats look good but I am going to meet with my machinist neighbor next week to use his small bore internal micrometer and other high end valve tools to measure the guides and go from there. For now, I wanted to take the head apart and get it clean.
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bagged and tagged.

I disassembled the lower end last night and was shocked to find a big gaping HOLE in both the top and bottom cases! @#%$!!! The DPO threw a chain, cracked the cases and "fixed" it with a crappy JB weld and thin aluminum plate. No wonder the motor was so heavily covered with oil and dirt near the drive sprocket. Originally, I suspected a bad seal was leaking oil. I often see chain damage on British vertical twin cases. Since they are vertically split, the damage is to only one half of the motor, but with horizontally split Honda cases, the chain blew out both halves of the motor. My friend Pat is a master welder and can work miracles with heli-arc/TIG and I will meet with him this week to access the damage and devise a solution. If the cases cannot be saved, there is another CB750 K4 parts motor in the Winona Riders' shop I may have to use. I would rather repair the original motor since all crank, rods, bearings, gears etc are in excellent shape. Hmmmmm.... Stay tuned...
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I had the crankcases cleaned in at a local machine shop to remove the residual oil before handing them over to my welder. He is going to start on them tonight and is confident he can save them.
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yuck...

I also cleaned the lower end components, cylinder and head and carefully measured the crankshaft journals, bearing tolerances, piston gudgeon, cylinder bore, rings etc. No surprises and everything is well within factory specification.
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The pistons were soda blasted and washed. They have some slight pitting on their tops, but nothing too deep and no scoring on their sides and they measure to factory spec.
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This is good news and confirms the motor has low mileage and is in good condition (beside the gaping hole in the crankcases) underneath all the dirt, grease and oil. If my welder finishes this weekend I should be able to prep, prime, paint and heat cure the crankcases and cylinder. Once my new piston circlips arrive, I will rebuild the motor. I am however going to wait to work on the cylinder head until my machinist friend returns and we can accurately measure the valve guides. Stay tuned….
 
On board! I'm interested to see how you repair the cases if that's the route you go.
 
Thanks all. Cases were welded tonight, all good! Full story and images tomorrow.
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Well Swan whats the main focus these days? The Goldie or the 750? Regardless the work you do is top notch and more. Your posts are some of the ones i look forward to the most!
 
Very entertaining read, good luck with the cases.
Decided on discs or 4TLS yet??.......after fitting twin discs I went with the shoes myself, completes the nod to the Brit look for me, in my head anyway.
 
Haplo84, trust me, I want to finish and ride my Goldie more than anything, but I need $1500 to do so. The snow is here and these Honda builds are money just sitting in boxes, so I am finishing them to sell in the spring and buy the last parts for my Gold Star.

MCR, I sold the GT750 drum a while ago and am go with stock-ish front brake set up. Drilled rotor, stainless brake lines, new caliper seal and master cylinder.

Case update; My friend Pat worked his TIG magic and saved my crankcases. I thoroughly cleaned the broken area with acetone and carb cleaner and later had them cleaned again at my machine shop. He tacked welded in some large pieces of aluminum with 4043 aluminum tig wire, wrapped them in insulation and let them cool over night.
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The next day he finished laying a bead around the tacked pieces following a template I made from another CB750 case we had at the shop. He used a piece of carbon to fill the hole in the top halve of the cases so I would not need to re-drill it.
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We wrapped them in insulation and allowed them to cool overnight. I ground, filed and sanded the excess weld to match the rest of the crankcase. Ideally this should have been milled, but I did it by hand using straight edges and a flashlight to carefully remove the excess weld to the correct level. The cases mate perfectly, I drilled and tapped a thread in the lower case and now need to find the time to clean, prep, prime paint and heat treat them.
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It ain't pretty, but will do the job and is much better than the beer can/JB weld patch that was there before.

While my cases were being repaired I cleaned, soda blasted,washed, tacked, primed, painted and heat cured the cylinder cover, cylinder barrel and oil pan. I used a light mist of Duplicolor high heat primer, and Duplicoler high heat aluminum 1615 and gloss paint 1613, dried over night then 45 minutes in the oven at 150, 200 and 300 degress F with a cool down period between each bake. I find this works well and makes the paint very durable and resistant to gas, oil and solvents. The pieces look great and I cannot wait to paint the cases and start going clockwise. Stay tuned.
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Nice work man, I'm all for good ol fashion hand working stuff,u prove if you take your time u can achieve good results , cases look well ;0)

Cheers Wayne :)
 
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