Topic: Updating 1975 cb750 with cbr f3 parts

[cb750frank]

Hello I am a new member and this is my first post. I purchased a 1975 cb750 about a month ago. this is a great site. I searched the forums for information and got it running and idling nicely in a couple of days. I am about to begin tearing it apart for a rebuild. I would like to update the braking and handling of the bike. I am not sure exactly what I want to do to the bike. Has anyone used cbr f2/f3 forks, wheels, brakes and rear swingarm with a mono shock. I am just curious how difficult this swap will be and any info or pictures would be greatly appreciated. I learned a lesson with my 1968 camaro in not planning ahead and having to back track. Dont want a repeat. thanks!!! Once again great site and great bikes in the gallery.

[nickjtc]

Welcome. I cannot help you with your specific request, but wish you all the best with your project. Don't forget to post pictures!

[.RJ]

The forks are probably not a big deal - you'll want the entire rolling front end if you can get it (forks, wheel, brakes, clip-ons, etc) and you'll need to order head bearings from all-balls to match the new steering stem diameter.  I can see that you might run into clearance issues with the clip-ons and gas tank, and maybe the gauges.  You might want to get an CBR F2 front end, since that uses a speedo drive on the front wheel (the F3's speedo is electronic) but I'm not sure if the 'gearing' on the speedo drive is the same - probably want to measure the tire circumference on the F2, and the 750.

The rear presents a more interesting problem, since there's not a whole lot of room to work with, and you'd have to relocate the battery somewhere, and either machine the swingarm to fit the frame, or use spacers.

Good luck!

[ProTeal55]

This bike is on Carpy's website --->

It can be done (and looks badass in my opinion). I just cant get past modern sportbike wheels...

[cb750frank]

Thanks RJ. I will narrow my search for cbr f2 front ends.

[rhinoracer]

Just because it's a Honda doesn't mean it'll fit.

Look for a fork assembly with a stem size that's long enough to fit the frame headtube with the races in the right places. Also look for stem diameter and make sure you'll find bearings in the appropriate ID and OD to fit both stem and head tube.

That will save you a lot of grief.

Good luck

[.RJ]

I just cant get past modern sportbike wheels...

I've had the same thought - the only answer really is to use a set of wheels off of a Motard (Suzuki DRZ-400, KTM, etc) but they are really expensive used for some reason - I've seen stock DRZ400 wheels go for $600-800 with trashed tires.

[eurban]

You are almost certainly not going to be able to simply locate a set of headstock bearings to fit a sportbikes front trees to the 750 headstock.  You will need to do some real work there.  You could have a set of trees made up with the correct spacing and fork tube diameters but with a cb 750 stem or you could probably have the 750 stem installed into the cbr trees.  Adapting the rear for a monoshock is going to be a huge amount of work but would be pretty unique.  Adapting a cbr swingarm for pivot bushing fit and for use with dual shocks would probably be a more reasonable approach.  Having a swingarm fabbed would be an option too.  If you want things to perform and be safe you might want to learn all you can about motorcycle handling/frame design/steering stem offsets, rake and trail etc etc.  Have fun

[FunJimmy]

I'm currently grafting a 2000 Yamaha R6 front end to my CB550 and it may be easier than first thought. The Yamaha steer tube is the same diameter for the lower bearing as the CB550, but the upper steer tube diameter is larger and overall length a little longer. I’m going to use the same taper roller bearings on the top and bottom, but the top bearing will be installed in the head tube using a bearing cup just like a bicycle headset. That will allow me to use the Yamaha triples with alloy steer tube without having to cut the length down.

Interestingly the 1999-2001 R6 triples have almost the exact same offset as the CB550 triples. This should keep the factory geometry as close to the same as possible.

While you are at the lathe making up the upper bearing cup, machine two bearing carrier/disc spacers to sandwich the front hub. Just like the spacers on this hub http://www.sohc4.us/forums/index.php?topic=26193.0
These will be the diameter of the CB front hub/disc mating surface and as thick as required to mount 1998 Honda CBR600 F3 rotors.

Calipers are the only thing I’m still working out. Yamaha R6 calipers are too wide and hit the spokes of the CB wheel. I’m looking at using other calipers or machining the mounting ears of the R6 calipers a little, combined with possibly milling a little off the inside of the caliper in efforts to clear the spokes. Must be careful not to breach the piston bores when milling the backs of the calipers though.

Update October 18th 2007 - The project is comming along well. New thread: http://www.sohc4.us/forums/index.php?topic=27159.0

[thefreeryder]

since i guess im not really a purist of ....well....anything....i have to say this bike looks amazing. I love it.

[Jinxracing]

If you go here:

http://www.ohiocaferacers.com/

In the tech tips section there are pdf files of just about all of the steering head dimensions and fork tube diameters you could ever want. Great resource!

[22kahn]

Im a newb here too but want to do something along the same lines. Ive got an 03 zx636 rear end and brake assembly, which fits very nicely into the frame of my 78 cb750. Im hopefully going to grind off all the excess tabs and weld on tabs for cb suspension, although I have been looking into a monoshock set up due to the elimination of battery and relocation of oil tank. In terms of the front end I was advised to go with a 91 z1000 fork tubes and HD hydra glide triples. (per at wrenchmonkees suggested it). But I found a cbr900rr front end with wheels and brakes that i might end up trading some bicycles for. So if that happens Ill let you know about the process and problems im going to obviously run into. good luck on your project man!

[Kale]

[Kale]

Sorry fot the late reply. This is my 1978 cb750. It has 1997 (?) cbr900rr front and rear end. There were slight frame mods but not too much. The ignition system was switched to electronic for electric tac. purposes and for better performance. It is deff possible as you can see..

[Silverback]

One of my favorite bikes!

Somebody posted info on it somewhere, but I can't find it now. I'm pretty sure this is an F3 conversion.

[dusterdude]

im not too sure where this project is at the moment,i will say,when i put an f3 swingarm on my bike,the legs(so to speak)were offset to the left of the frame a tad and therefore the shock on the right side did not lay on top of the leg of the arm like the left did,ala the stock swingarm.thats the only real issue i faced,so i put the stock arm back on the bike.

[Variantbuilder]

i was curious to what rear suspension is posted in the picture? I am in the process of putting on a 07 yamaha r6 front end and need some rear suspension to balance out the bike.

[Jwexperience]

I put the later cb900/1100f shocks from the early 80's on my bike. They're longer than stock and make turn in a little quicker but handling is pretty nice, it doesn't feel like it is falling into a corner.
My bike is a '78 cb750f with '06 gsxr600 front end and 17" wheels front and rear. Offset is stock gsxr.


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[Variantbuilder]

Thats Awesome! so the gsxr rear wheel fit ok on the stock swingarm? i really want to try getting an 07 R6 rear on mine and im not sure how to make that happen. i own a 76 cb750 k

[Jwexperience]

Thats Awesome! so the gsxr rear wheel fit ok on the stock swingarm? i really want to try getting an 07 R6 rear on mine and im not sure how to make that happen. i own a 76 cb750 k

I think that will take quite a bit of work. My rear wheel is off a cbr600f2 and is a 150 series tire. Your tire is most likely a 180 and I think your swingarm is a little narrower than mine. Plus the chain alignment would be tough to overcome as well. I added a offset front sprocket to move the chain out a little and your sprocket is even more inboard than mine was in stock form.


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[Variantbuilder]

Hmmm yeah it is a 180. Dang I was hoping to make this happen to keep both rims the same. Thank you for the info.

[Variantbuilder]

Found some info here: http://forums.sohc4.net/index.php/topic,40729.msg1892673.html#msg1892673

[PeWe]

I put the later cb900/1100f shocks from the early 80's on my bike. They're longer than stock and make turn in a little quicker but handling is pretty nice, it doesn't feel like it is falling into a corner.
My bike is a '78 cb750f with '06 gsxr600 front end and 17" wheels front and rear. Offset is stock gsxr.


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Nice build!!

[Shtonecb500]

I put the later cb900/1100f shocks from the early 80's on my bike. They're longer than stock and make turn in a little quicker but handling is pretty nice, it doesn't feel like it is falling into a corner.
My bike is a '78 cb750f with '06 gsxr600 front end and 17" wheels front and rear. Offset is stock gsxr.


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What did you do for the rear? I just picked up f2 wheels and im starting to think the rear wheels fits into the 77-78 swinger.

[madmtnmotors]

What did you do for the rear? I just picked up f2 wheels and im starting to think the rear wheels fits into the 77-78 swinger.

You will note that Jwexperience is listed as "Guest" which means no longer a member here, and for good reason. He was banned from this forum multiple times under multiple user names (and many other forums as well). The picture of the bike he posted was likely copied from somewhere else so he could claim it as his own without really knowing anything about motorcycles or mechanical related topics. Some of his continuing antics are documented here:

http://forums.sohc4.net/index.php/topic,163088.0.html