Topic: 1978 CB750k. “Bottle Rocket”

[csdawson97]

Hey all. Bought this off a guy the other day after selling my CB650 Nighthawk. $500 with a title. Came to me exactly as pictured along with 3 tubs of the smaller parts. Motor is free and has compression, that’s all I know. Supposedly it was running and a daily rider before he disassembled for a cosmetic restore. Second pic is before he disassembled. I have a vision in my head of a shiny Honda Red and White cafe racer blasting down the mountain and will be slowly sculpting it over the fall and winter. Here’s my plans for it as I have them now.

Full motor rebuild with pistons cams and connecting rods set up for a twin Garrett GT12 turbo setup. (Maybe a pipe dream, that’s another thread entirely)

Frame detabbed and powder coated white

Seat pan and hump painted and most electronics relocated to hump. (To help balance weight if I go with turbo setup the way I want)

Different tank, possibly with integrated oil tank.

Large oil cooler with electric fan to handle additional oil cooling needs of turbos.

Front end swap, haven’t decided on donor yet, been looking at triple tree kits at cognito Moto. Any suggestions?

So far that’s about it, everything else is still floating around. Pics and updates will be posted here, specific questions will be asked in their respective forums. Any and all suggestions are greatly appreciated. I’m 20 and have been working on bikes for the past 4-5 years. I don’t have much (read; any) experience with internals or cracking cases so hopefully this will prove to be a great learning experience where I can pick up knowledge from the wiser minds on here.







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[calj737]

The Cognito hubs do make front end swaps rather easy. You pay upfront for the “plug and play” ease, but it does save heaps of time and errors and custom machining.

If you are have never busted open the internals on an engine, your Garrett turbo-driven aspect might be overly ambitious, this time. Perhaps keep that as a Stage 2 project with another donor motor. Rebuild this one, normally aspirated and bumped up to get yourself acquainted and determine if that investment is where your heart really lies.

In a slightly HP bumped condition, riding an old bike fast is heaps more fun than riding a fast bike slow.

[csdawson97]

The Cognito hubs do make front end swaps rather easy. You pay upfront for the “plug and play” ease, but it does save heaps of time and errors and custom machining.

That was my thinking, I don’t have access to a CNC so everything would have to have been made by machine shop, I figured I’d spend more in trial and error.

If you are have never busted open the internals on an engine, your Garrett turbo-driven aspect might be overly ambitious, this time. Perhaps keep that as a Stage 2 project with another donor motor. Rebuild this one, normally aspirated and bumped up to get yourself acquainted and determine if that investment is where your heart really lies.

That’s certainly a possibility, I will likely see how I feel once I have it open and see how comfortable I am, and how in depth I’m able to grasp it. Do you have any suggestions for learning a motor rebuild?

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[calj737]

In my opinion rebuilding a motor to stock-ish condition is vastly different than building a HiPo motor. The Service Manual it Mark Parris’ Book (Hondaman) can get you thru a full re-build. But dialing up a motor to accommodate and take advantage of a turbo is not for the uninitiated.

If you’re going turbo, you need to use HiPo crank/rods, chains, pistons and valves. All that has to go to a machine shop. And they don’t work on trade... It can all be done, but more people are bound to abandon a lofty project than complete it. And if you’ve never owned one of these bikes, you might just wait and get it running and decide you love it before you invest $10-$12k in building a motor for it.

Should you pursue it, I’m sure there will be no shortage of advice and caveats forthcoming. Everyone here likes to see people succeed.

[RAFster122s]

I feel it would be foolish to think you can build a turbo or twin turbo bike with no experience building/rebuilding motors. A turbo bike is not simple as a bolt on affair to a stock motor as Cal has tried to briefly explain. You can easily spend 2-3000 for a nice mild  high performance motor without the added complexity and specialized parts needed for a turbo bike.  You are going to have to be pretty skilled at diagnostics and tuning for a turbo motor as well.  Over boost a turbo motor and you can end up blowing up the motor or melting a piston.

Sit down and calculate what a normal rebuild will cost you using a tried and true kit from Dynoman or similar.  Expect to double that cost with unforseen expenses the first time around.  Consider your motor to require a complete rebuild with new gasket set, pistons, rings, machine work for cylinders. Total top end valve job with 1/2 the guides or all the guides replaced and the machine shop time to get new guides honed to size and new valves and springs. New hardweld rocker arms as most all cams are hardweld rather than a new grind or billet camshaft.
Throw in primary chain and tensioner and guides along with a new camshaft and all new oil seals
Oil pump overhaul or replacement and overhaul.  New clutch discs and new clutch steels.  New Honda Cables for throttle and clutch, speedo, tach.

.
New drive chain and sprockets

[SOHC4 Cafe Racer Fan]

We are not trying to piss in your Cheerios, but both if you have not done an engine rebuild before, that's going to be enough of a challenge for your first rodeo.  A proper normally aspirated motor can run you easily in the $2-5K range.  Adding a turbo creates even more complexity because these motors were not designed to handle the higher stresses. You will end up having to spend more on rods and your valve train. 

[csdawson97]

Welp. Due to both the loads of contrary advice and today’s purchase of a Monster 900, my desire for a turbo 750 has been reduced. I will likely, if anything, boreover and leave NA, if not just rebuild.


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[RAFster122s]

Better really to buy a turbo bike that is not known for massive issues.  Once sorted the CX650Turbos were entertaining.

Surf over to Motorcyclist and read their article on Turbo motor cycles from the 80s.

Even with a factory turbo bike it is no bed of roses.  If you run a turbo hard you need to let it cool down before shutting down.  Even if it is a water cooled turbo you end up cooking the oil a bit after shutdown as bikes are not going to have post shutdown circulation pumps to cool the turbo.

I would rather build a supercharged bike, but even then, best done with a FI bike for ease of programming fuel curves and ignition curves to suit...
But, I do not have the skills to do it at this time.  Not to say I could not learn, but it would be a journey and a learning curve to overcome.

As Clint Eastwood once said in one of his movies, "A man's gotta know his limitations. "