I’ve noticed a lot of people freak out when something they rely on breaks or malfunctions. Anything from a flat tire to a dead battery in a phone, your average user tends to grimace and call a serviceman. Or just buys a new one.
I love fixing stuff, so I always wonder why they don’t get the manual out and have a bash. The typical reason is ‘I don’t understand this stuff. Things are so complicated these days.’
What, did some advanced alien race build your car? Is that smartphone an object bequeathed to us by godlike extra-dimensional beings?
Sure, almost everything is built somewhere else these days (particularly in Australia), but people still make this stuff. Not evil genius robots who cackle mercilessly when you try to re-set your dashboard clock.
Despite the litany of your average creationist, I firmly believe one of our ancestors climbed out of a tree, picked up a bone, and bonked its neighbor over the head with it.
Was the bone too complicated to hold correctly? The instruction manual in too many languages to read? The whole job of becoming the dominant species just too complicated?
It certainly was for the hairy proto-human lying in the dust, forever removed from our genetic pool.
Adapt (and achieve) or die, people. When you teach yourself to use tools, to fix something, you learn how to learn. Ignorance is a weapon used by politics, religion, marketing, and journalism. Avoid it on all fronts.
Which is why I hauled this wheelbarrow of motorcycle junk into my shed. Comfortable in the knowledge that guys like Soichiro Honda didn’t care how hard it was to stick a motor in his wife’s pushbike. It needed doing, so he did it.
For building Cafe Bob, I don’t know where I’ll start, but I have an idea where I want to finish. Will it change as I go? Will various ideas fall over, to be replaced by better ones?
Of course. Evolution never started, nor ended. Some folks just prefer to ignore it.
Enough prattling. About the donor bike.
Unloved By All But Andy
The DOHC (Dual OverHead Cam) Honda CB750 was launched to very faint praise in 1979. Sadly, its forebear, the SOHC (Single OverHead Cam) CB750 was a revolutionary motorcycle, swinging a well-aimed bone across the head of a flagging British motorbike industry. SOHC CB750’s are now very collectible, and getting your hands on a pile of bits to tinker with very expensive.
So, thanks to the lack of love for the model, I have a pile of DOHC CB750 junk my mate Mark had in his shed. He had several loads worth, and gave it all to me under the simple agreement of doing something with it.
We like Mark. Buy some booze from him (head to winedirect.com.au). I suggest the Bird in Hand Sparkling, which does a great job of ridding your mouth of Shed Aftertaste (that mix of WD-40, old motor oil, metal shavings and blood licked from your knuckles).
Now, the DOHC CB750 has a few flaws, most of all being weight. Every component seems to be made of recovered battleship steel plating. It is a boat anchor compared to svelte Italian fare of the same era. (There was a logic to this, as Honda grew it into the CB900 and CB1100 without adding much weight.)
The advantage for a barbaric tinkerer like me? I can hack great big pieces off of it and it will still work.
(I take some advice from Andy. He’s a supreme tinkerer of DOHC Hondas, and has carved several into woundrous bikes.)
For this build, I’ve set up some basic principles on how to approach it. I won’t use the term rules, as rules should never apply to a project. (And yes, I have project managed a number of complex things to fruition, and delivered them on budget and on time. It requires rules that create compromise in the final product, which is simply unacceptable when I’m making a toy for myself. So shut up.)
Principles of The Build:
#1: If a single task requires a specific tool, don’t buy it. Make it. If folks can make Phasers out of old Blu-Ray drives, I can certainly fabricate a valve compressor.
#2: If the tool will be used only moderately, buy a cheap one. I spent $20 on an angle grinder. Folks tell me it will break. It hasn’t (yet).
#3: If the tool will be used regularly, buy a good one. A good set of wrenches can be your lifelong friends. My bench grinder, which is regularly punished for being indestructible, cost heaps.
#4: Do not consult experts before you start. Not having a clue promotes fresh ideas. It’s good to have them cast an eye at critical stages of completion, but don’t let that stop you getting the damn thing finished.
With that in mind, here is a small portion of what dwells in my primitive Shed. I’ve been swingin’ bones, hoo yeah!
This week was brakes. Digging through the boxes I found the original front single-piston calipers, the rear caliper, and some of the brake lines. I had three master cylinders: Two different ones of equal scunginess for the front, and the original rear master still hooked up to the line and the caliper.
Both the front masters were utter crud. Reservoir bolts snapped off in the main casting and crash damage. If you’ve ever salvaged a bike, you know what they looked like.
The rear was even worse. Corrosion was evident in the brake line when I unbolted it. Oh dear.
So I peeled back the boot on the thrust pin for the master cylinder, going into the bore. This is what I found.
Oh DEAR. I’d spend more recovering this piece than I would on dental work. I moved on.
The fronts were in better shape. Much to my cheap-ass delight, I realised the crossover tube for the front forks (which allow you to add pressure to increase preload on the suspension) would thread into the front calipers. All I needed do was cut up a threaded rod to thread into the brake line inlet on the caliper, drill a hole through it to let air pass through the rod, then screw it all together.
Clamped the other end of the rod onto my air foot-pump, jumped on the pump a few times, and pop! Out came the pistons.
Rummaging around the top end of the engine, I discovered I had three complete sets of chains. This model has a strange assemblage of chains in the engine: The main Morse chain heading from crank to layshaft, then crank to exhaust cam, then exhaust cam to inlet cam. Certainly one from each set would be usable. I also had six camshafts, when only two are required. It is a DUAL-overhead cam motor, remember.
Knowledgable Andy noted the numbering on the cams. Some were for a 750 motor, some were for a 900. Checking the manuals tells me the 900 had different lifts (and likely durations). Hmm.
I’ll think about which ones go in.
Now, some folks may think I got all kindsa ed-jee-cashun in things mechanical.
Actually, no. I went to art school.
Most of what I have learned was from the late, incredibly great Cycle Magazine. They wouldn’t just review bikes, they took them apart. Glorious full-page spreads of engines disassembled and laid out on white sheets. Amazing. They would talk about the artistry in the engineering, name the component, and show you what they were talking about.
It was glorious. With that knowledge, I destroyed many a motorcycle in my younger days. In one case I went through four sets of pistons trying to get a beautiful red Yamaha RZ-350LC to stop seizing at full throttle.
If I had the interweb back then, I would have figured out it was cold-seizing after the first set of pistons (the previous owner had removed the thermostat). But what I learned about water-cooled two-stroke motors? Premix pumps? Invaluable.
In that spirit, I’ll swing some bones at the frame and wheels next…