Topic: "Zasshuken" Monoshock cb750 build

[cbxr750]

Hey everyone, ive been looking around the site at some other build and decided it was time to join and share mine. I purchased a 1975 cb750 in August for $300. It ran and rode but looked horrible. Previous owner had put forward controls, aftermarket bars and some crappy flat black paint on it. That weekend I had it torn down to the frame and sold all the parts I would not be using. So essentially i had a free bike. A good friend of mine had a wrecked GSXR 1000 from 2001 laying around so I purchased his complete front end and sourced a 1988 GSXR 1100 swing arm, 750 wheel with sprocket, rotor and axle. Detabbed the frame and got rid of the shock mounts. Had a guy in Colorado machine me some brass bushings that would allow me to use the stock pivot bolt with the new swinger. Build is at a stand still now until i can get the funds to buy all the parts below.

Gauges – reddragonfly speedo and tach
Cognito moto retro nut
Cognito moto gsxr kit GSX-R1000, GSX-R750, GSX-R600 BILLET TOP TREE 2000-2004
Stem with bearings pressed bottom triple
Autofeel 7 Inch Round Philips Led Headlight
Dyna s ignition with coils and wires
led flexible tail light with signals
cnc aluminum levers with master
regulator/rectifier ricks motorsports
8cell antigravity battery
Cyclex exhaust
CB750F REARSET BRACKETS GSXR MASTER CYLINDER CONVERSION
Rear sets

Hardest part on this build will be the monoshock set up. I hope to run the stock 88 GSXR linkage and shock. Tail section will have a custom oil tank and the seat will be bolted to a cafe style carbon fiber design. Keeping the stock tank but will be painted candy red. Frame and swing arm will be cadillac black diamond. debating on the wheel color still. Motor work will remain minimal, just ignition and exhaust for now and keeping the engine chrome/aluminum. not painting the engine unless it doesn't clean up well.

Since i have some down time with the build, I wanted to start a discussion on the suspension. I want to keep the geometry as close as possible to the 88 GSXR design. What is everyones thoughts on that?

[cbxr750]

[calj737]

Aside from offset, rake and trail numbers, you also need to consider the swing arm angle from the pivot rod to the axle. Bike-to-bike swaps don't translate exactly, but the modifications your making with grafting GSXR parts front and rear should work pretty well. You might give some consideration to additional bracing of the stock frame to support the components.

A "frame kit" on a 750 is a very nice modification too allowing easier install/removal of the engine, and servicing of the engine while still in the bike. You should also consider installing some DIY "Steering stops" on the lower tree to align with the stock neck. Check out Cognitomoto's trees from an example, or add one of his trees to your Wishlist 

[cbxr750]

Yea Im sourcing most of cognito's parts. the triple kit from there will be my first purchase and the offset sprocket to line up with the rear. Also, i should add that the swing arm is upside down in the picture. wanted to see different options for the shock. the frame will have considerable bracing where the shock mounts up. ill take a look at the frame kit. Wheel base now is 6in over stock. Its going to be like riding a mini tank haha but should be quite stable on road.

[SOHC4 Cafe Racer Fan]

Welcome to the forum.

You may or may not have considered that the GSXR swingarm is significantly longer than the original. I don't know your knowledge and experience level. The extended wheelbase will affect your ability to turn the bike. It will handle like a drag bike and be very difficult to turn quickly.

You should also consider painting the engine, since you will never clean the oxidation off the fins, etc. without blasting, and the rest of the bike is being powdercoated and painted. Otherwise, the engine will stand out in a negative way. You can still clean and paint the engine as a whole unit, and you already have it out.

[cbxr750]

Thank you! Ive worked on cars my whole life and built a 89 Radian last year. I have been pouring over information on suspension design. i know it will not handle the twisties well compared to other bikes. im ok with that. as far as the engine, I have a soda blaster i may use on it. Ill take a look when i get it on the stand. I just dont want it all black since thats played out. Im open to suggestions however!

Trying to sell the radian to fund the CB.

[calj737]

Maybe a new rear tire would help sell it? 

[cbxr750]

Good thing I put new tires on  lol

[SOHC4 Cafe Racer Fan]

You could in theory shorten the GSXR swingarm by sectioning it, but you'd want to reinforce the splice with some great welding.

[cbxr750]

This is true. Also, I believe they had 2 lengths for this year and this is the longer one? I remember reading something on that. I dont mind the longer arm. Looks mean with the big motor and big tire.

[Retro Rocket]

This is true. Also, I believe they had 2 lengths for this year and this is the longer one? I remember reading something on that. I dont mind the longer arm. Looks mean with the big motor and big tire.

It may look "mean" but it will handle like #$%* as has been pointed out, if you only want it for looks then go for it, If you expect it to handle better, or even close to stock it won't...   Just saying, don't get upset....
PS, you can't turn a monoshock arm upside down and expect it to work, the linkages are designed to give a specific rising rate to the shock....There are a multitude of reasons why "keeping the 88 GSXR specs" on the suspension, won't work, the ONLY way to achieve that would be to put the 750 engine in a GSXR1100J...

[cbxr750]

Totally understand. I know its not going to handle close to stock. Not building a race bike. the arm upside down was just for mock up and experiment and I know it wont work. As I am not a professional in suspension design and geometry, I figured the best way to go was to keep the arm and shock as close to the stock design on the bike it was meant for. Also the reason why i am here, to get constructive criticism on how it should be set up.

On a side note, I am going more for looks. I hate street bikes. They are a dime a dozen in my area which is why i opt for different. Im going for some thing that turns heads but is also ridable. Speed and dragging knees is not my thing(not many 22 year old guys saying that  ).

i do appreciate everyone's input!

[SOHC4 Cafe Racer Fan]

I would suggest that you alter the swingarm to fit the frame versus the frame to fit the swingarm. It is very possible you will change it after having to fight the bike to turn it. Just a friendly suggestion mind you.

[cbxr750]

Define altering the swingarm? I bolted this right up with different bushings. no modifications to the frame to fit

[SOHC4 Cafe Racer Fan]

Define altering the swingarm? I bolted this right up with different bushings. no modifications to the frame to fit

Depending the rear wheel used, you will still need a brake arm stabilizer.  I would adapt anything on this rear end to fit the stock frame versus the other way around.  That way you can easily swap out the swingarm for a more functional option.

Ideally, if you wanted the bike to turn (maneuverability is not underrated as a safety issue), you might want to shorten the swingarm by at least 4 inches.  This would require some tig expertise, to not only reattached the sectioned out swingarm portions but to reinforce the re-attachment point.  This would really take your build up a notch.

I know that this is your bike.  This is just some friendly advice.  I have actually ridden bikes with extended swingarms.  They feel heavy and turn like pigs.  If you intend to ride on the street, you may need to turn, swerve, etc. and a six inch wheelbase extension is even more than many drag bikes will use.  Do you really want a bike akin to this ...

[cbxr750]

I agree, the length is quite large. i think i may get everything mechanically finished before paint and powder so I can test ride it and see how it performs. I can have the arm shortened if need be. Not able to tig but i have connections. once i have it rideable i can make a better decision. and no I dont want to look like a stretched busa haha. I have spent money on this arm and I would like to make it work for the build so I will modify it need be.

Ride height plays a role in this as well correct? I feel if the angle in the back is raised slightly it will turn quicker. not going brian fuller on you guys, dont worry 

[754]

 I ran 6 over on the street on my 836, for the most part I liked it.
the paert i did not like was parking , or rather parking with other bikes jamming me up. And I could not run my 54 tooth rear without going over 120 chain links...harder to get the long ones.
 So ideally I am now shooting for 4 1/2.. hope the front end stays down.
 Sure is a lot more stable on the highway..sorta like that..I dont corner hard either, and had no rear shocks, but still rode hundreds of miles a day.. rode it 950 miles to Bonneville from here.

[cbxr750]

Yea im in the same boat. never rode anything this long but i like the idea of the stability as well. We will see how it is after all is bolted up. its killing me not being able to work on it right now.

[calj737]

Yea im in the same boat. never rode anything this long but i like the idea of the stability as well.

Since cornering isn't your primary concern, and you want increased stability, maybe a 3-wheeler is your cup of tea? 

Be prepared that if you undertake sectioning that GSXR arm, you're in for quite a bit of work. It may well be that the arms tied to the pivot tube are much longer than stock, and therefore a straight sectioning won't shorten the arm as desired. It may necessitate 2 completely different cuts and filler material to bring back the spacing, geometry, and length. If the axle end of the arm is long enough, then you are far better off in shortening the arm and moving shock mounts. But I don't know that arm particularly well....

MY opinion is a 1" over 550 arm or 2" over 750 with a GSXR front end would be about the perfect geometry for handling, stability and braking. Adjustable front offset triples too.

Keep getting it, just don't go too far down a path that cripples your project if you need to abandon certain ideas. Thats when these projects die due to disappointment and aggravation.

[cbxr750]

Actually i saw cyclex has a pretty trick 3 wheeler 750 haha but yes, i am going to get it to a rideable setup and see how it is then go from there. That way i can pull the arm and shorten or source a similar arm with less length.

Side note. Devin came out with a cnc air box. I want it!
http://cognitomoto.com/collections/new-products/products/cb750-air-intake-box-sohc-and-dohc

[SOHC4 Cafe Racer Fan]

I agree with Cal's recommendations re swingarm if you want a nice handling bike.

I have the same setup on my modern fork projects.

[cbxr750]

well that brings me to the next question. not sure if you all are familiar with 1st gen gsxrs but what arm has the same pivot bearing size? if I can source a shorter arm with the same bearings, I can use the parts I already have. I may need to find a different axle but those are only $25 bucks. also would like to use the wheel i have since i dropped more $ than necessary on it. its a 750 wheel but same year range. I can use this arm for a different build if need be. maybe a kz1000 drag bike 

[SOHC4 Cafe Racer Fan]

I have no idea in terms of the world of fitments for GSXRs.  GSXR.com and gixxer.com are forums that might be able to offer you some additional information.

Frankly, it will be cheaper for you to buy a used CB550 swingarm, and mod it as Cal suggested.

IMHO, the ideal (but much more expensive) solution would be to use a modern box-style swingarm made specifically for your frame and application, like a CMR Racing swingarm.

[SOHC4 Cafe Racer Fan]

You should also ask Ilja as he did a similar GSXR swingarm bike.

[cbxr750]

currently drooling over the swingarm you had made.....but cant justify the money. joined gixxer.com to see what my options were also found a cross reference on the bearing part number and have a list of bikes using the same bearings. now to find the width of the pivot sections. hopefully i can figure out a similar arm. in an ideal world i could find a wrecked bike and use the entire rear section with suspension. While the cb550 would be a viable option, I want the gsxr swap. something about its challenge and engineering to make it all work gets me going.