1974 CB750 Built from Parts w CBR600 Front & Rear

[Frankenfe]

As I wind up my first “Café” build of a red headed stepchild - "CM400T" - I realize I truly enjoyed the whole garage build, creative & fabrication process. I have taken all the ribbing for the platform I chose to work with and the “café” approach with the challenge of the CM twin’s more modern “Dropped Cruiser Frame” pressed steel frame.
That said, after cutting my teeth on the process I couldn't wait to start the next build before finishing the twin.

Basic Criteria was
• Stay with a Honda
• Use a (+-) ’78 and earlier flat line frame (Ok I get it now I like the straight line)
• Since I have a “Twin” I wanted a four

So it would be a CB 450/550/750 Four. I have a 95% Stock Original ’71 CB750K1. So nice & original - I couldn’t molest it, I wanted to …but had too much respect for it. A smaller four would be nice, a little lighter and more nimble, but to own a highly modified 750 and a stock one would be cool.

Here is the early 71 K1 as I got it and after I got it (Removed the '70s Accessories back to naked stock. Except for the small case savers that in my opinion look ok. Bummer that he decided to paint the bike to match the vetter accessories instead of The Accessories to match the bike. Some Day I'll have it painted back to OEM Green. The original seat was still in the box the touring seat came in so it went back on.
,

 

[Frankenfe]

Re: 1974 Built from Parts, CBR600 Front & Rear

If there is one thing I learned in the Cafe process is that there are truly few parts that are needed by the time you properly strip it down. So rather than molest the K1 I decided I would build it from gathered parts.

Afterthe CM Café had been sort of a Reverse Engineered Design, (Mags to Spokes, Front Disc to Drum) this next build I wanted to do a “Tech Forward Vintage” or “Resto Rod” approach. This amounted in my mind, Front End, Brakes and Wheels so going the completely parts route seemed right.

Then my inspiration came with the tank. A Dicks Cycle West (of the 70's) "Racer 1" Tank. The "Street" Version(Pocketed in the end to accept/cover a stock seat). The original design Full / Race Version was a copy of the JapAuto French Race Team and used to win the Bol D Or in the early seventies.

 

[Frankenfe]

Re: 1974 Built from Parts, CBR600 Front & Rear

So I needed a frame and I needed a Modern Sport Bike Willing to give up its front and rear.

A quick search showed most wanting in the $400 range for the parts I wanted so I began to wonder if buying a whole bike and kept what I wanted ....to make a long story short that is what I did. Bought a 1998 CBr600 F3 Complete not running but not frozen for $500. Sold all but the Front End - Triples and Clips toWheel and Discs and Rear Swing Arm with Shock brakes and wheel. When all done My Parts free & $107 in the pocket.

A Titled BARE Frame (No Swing arm or Engine Mounts) with a new "Carpy" 4 into 1 and a few other odds and ends for $200.

Research on the CBR600 Front End looked promising so a $24 ebay Tripple tree became a donor of a stem. Ground the Welds on the bottom of the lower tripples press out - press in - weld it up and put it together with a new set of All BallsTapered Bearings and Boom More Modern Brakes Forfs and a lighter wheel that will accept more tire.

I quicly Realized I was not going to try and engineer the Mono Shock Transplant and I really wanted a more vintage feel (Silver Wheels, Black Frame, Clean Vintage Engine, ...) Additionally the PO had bumped up to a 180/55-ZR17 from the Stock 160/60 I could see even a 160 was going to be a challenge with Sprocket alignment and clearance and tire clearance on an early pressed seam swing arm. A little research and off to ebay for an Early DOHC Swing Arm. $30.35 Shipped for a "79 with Axle Bolt (CBR and 750 are same size) I also like the look of the Tubular design of the later Swing Arm vs the Seamed "Early" Swing Arm. There is an issue wuth the width at the pivot point, I cut off some from one side only (Some say a little from both). And the Arm is about 2 inches longer as well...more on that later.

Cleaned up old set of Bushings and a couple old shocks and I have a roller.

 

[Frankenfe]

Re: 1974 Built from Parts, CBR600 Front & Rear

I Really had more than a "Roller" by the time the above pic was taken. I had done the tab removal of everything, yes even the center stand spring mount, horn mount and brake pivot tube. The only things left in the pic (that ultimately came off) were the Oil Tank tabs, Side Kick Stand, and Rear Fender stays.

I will use a Track Stand in the garage and a (Yet to be Engineered) removaple / packable side stand with "Stealthy" mounting.

You will notice the CBR600 also donated the Rear Sets, complete with Linkage and Master Cylinder / Line. Mounted with a set of welded on Threaded Bungs on each side.

I had also decided on fabricating an Oil Tank out of aluminum that fit in the rear "Pocket" of the tank (Designed to accept the OE Seat) This would kill 2 birds with one stone, open the frame up and finish the tank visually. I tried to just continue the lines of the Gas Tank.

 

[Frankenfe]

Re: 1974 Built from Parts, CBR600 Front & Rear

I was really struggling with the what kind of front fender or no front fender. the 17" but Wide front tire made a vintage difficult with larger diameter wheels and "Arcs", I eventually stole a 2004 Ducati 999 front fender off ebay for less than $12 shipped.

 

[Frankenfe]

Re: 1974 Built from Parts, CBR600 Front & Rear

I wasn't satisfied with the look and eventually settled on cutting the rear vertical portions off. Then the challenge came on how to mount them. I made up a set of adapters out of aluminum.

I had also picked up an '84 CB650SC Oil Cooler and added shock mounts by this time. Other mounts added were New Mounts for aluminum Under Seat Trays, Rear Master Cylinder, 4 into 1 Exhaust end mount and new Fork Stops.

 

[Frankenfe]

Re: 1974 Built from Parts, CBR600 Front & Rear

Working out the venting, return and feed lines before closing up.

 

[Frankenfe]

Re: 1974 Built from Parts, CBR600 Front & Rear

A $17 Cap and Bung with scavanged Barbed Fittings from stock lines for Return and Feed and aluminum Brake Line for internal Vent. Closed it up.

 

[Frankenfe]

Re: 1974 Built from Parts, CBR600 Front & Rear

So this is pretty close to where it is at now. I'll post sone picks of the trays, and I have an interested Possability vor a Vintage Headlight / Tach I am working on that I might use.

also picking up small things like grips, throttle, horn button and all metal pegs to replace the CBR 600 pegs.

 

[Frankenfe]

Re: 1974 Built from Parts, CBR600 Front & Rear

I will also post some pics of the Cosmetically nice '75 CB750F0 I picked up with a Truck Load of parts for $100. I want some nice custom and vintage parts on the engine, but NO Finned Covers. I have an interesting Oil Preasure Gauge adapter that came on an old engine in the truck load as well. Here is an oil line adapter I picked up in an ebay CB750 "Lot"

 

[Rattlecan]

Nice I'm signed up! This build looks like it could be pretty cool keep up the good work.

 

[JustinLonghorn]

Yep, I am on board.

 

[Maritime]

Me too. Nice work so far, tank in the tank was an awesome idea and with the cooler should give you enough volume.

 

[Bobbed_out]

Pretty cool...

 

[Frankenfe]

Thanks all, I will try and keep it moving.

I had an opportunity to pick up a set of Keihin CR Street Carbs, used but appear to be in good condition. Missing an accelerator arm, but found a replacement. Came with K & N Filters and I picked up a Newset of Original Black Plastic Velocity Stacks. Not sure what I will use, plenty of time to decide.

 

[surffly]

So the rear CBR wheel bolted on to the DOHC swing arm? and all it took to mount the swing arm to the SOHC frame was alittle grinding?

 

[Frankenfe]

surffly,

Evidently when the DOHC frame was designed, they made it a little wider. In my opinion it is all added to one side (one side protrudes a little more than the other) I used a cut off / box saw to cut mine so it would be square and flat.

I currently have the old tire on it, a 180/55-70 and ther are no tire clearance issues. (I will go back to the original size of 160/60-17 maybe even a 150/60-17) Clearance with tire and Swing Arm is not the issue. It will be centering the tire as much as possible while alligning with the sprocket. An off-set engine sprocket and probably mill work on the wheel hub to move the sprocket in will be required.

The Axle Size of of the '98 CBR600 (Wheel) and '79 CB750 (Swing Arm) are both the same, 20mm - If I remember correctly. a fabricated to fit spacer(s) will be necessary. Length of the axle bolt was not an issue.

The DOHC Swing Arm is about 2" longer than the SOHC swinger. This puts the Wheel and the Lower Shock Mount Further Out. Some will like the longer wheel base others won't. But the real issue is the Lower Shock Mount. using Stock CB750 Shocks will lower the bike almost 2 inches. Not what I am looking for actually I wanted to slightly lift the rear. I will be moving / adding shock mounts at the point they would be on a SOHC Swing Arm (about 2" inward) I will also be using a little bit longer Shock 14.5".

I am foolishly attracted to the CB900F Shock and its racy but vintage look. "Foolishly" because I know they aren't good techcnology and all that can be found will likely be beat to hell and as I understand it, are not rebuildable. bought a pair cheap recently off ebay. I have seen them go for as much $280 a pair, so I am comfident I can get my money out of them and they will look good during mock up.

Pic Below shows another loer shock mount about where I will cut & Weld in. Notice the "Tubular" Construction of the Swing Arm.

 

[Frankenfe]

Here are some more pics of the Oil Tank & Gas Tank mated up & on the Bike, and the beginning of the seat.

 

[Frankenfe]

Pics of trays for electrical, (Cut out for Oil Lines) Currently Oil Breather, Fuse Box, Ignition Switch and Starter Button are mounted.

 

[Frankenfe]

Better Pics of the Fender and the headlight I have been working on. It is a CL77 headlight with a 1980 CM400 Tachometer adapted to mount in it. I cut and shaped a ring out of 1/4" aluminum.

I went with a tach only because the CBR front end ran an electronic speedo and I am not up for that challenge. So I went "garage" and the path of least resistance using what I had. I did mount the tach turned for the look as well as the routing of the tach cable. Gotta love the Horn mounted in the back of the headlight too.

I am not sure I am sold on this headlight though. The small diameter looks a little odd to me with the enormous tank, beefy forks and fat rubber ????? I would like a bigger deeper bullet shape I think, we will see.