sorry brookesy I was away fro the weekend.
No offense taken by the way, I know you went trying to bust my chops.
Issues that i need to look at are exactly as you mention
Frame bracing and rear swingarms and also pushing the sprocket out to match the new rear end
It's a pity there's not something like the Katana site where there's details of how to brace the frame
looks like someone has done a finite element analysis of the frame (i assume again) and added strength where it's needed most
It sounds like we're on the same planet anyway - one of the ideas i'm throwing around is exactly that - getting a CBR600 swingarm
and adding shock lugs. I don't want the rear wheel though (if i go that way) and i'm not sure (yet) how i would put a spoked wheeel on it.
I need to do some more hunting for info before a make final decisions.
USD front end??? not sure...
any suggestions for info on this stuff?
i'm sure the look i want for the rear could be covered by a nice braced alloy swingarm and Ohlins shocks
cost is always a factor - and sometimes spending more in one area can save more in another
the answers to these and other exciting questions will be answered in time
I'll try looking for some streetfightered SOHC cb750s for you, I had a whole collection of pics on my home comp but I am not there right now.
If you want to keep a spoked rim, it kinda limits your options and you may have to do some leg work. The only bikes that use spoked rims these days are crusiers and the rims are heavy or dirt bikes where the rims are skinny. you can get aluminum rims to lace to the hubs but the hubs will still be heavy. You can try keeping your original rims and adapting them to the new forks but you will need custom spacers and brake mounts. One option you might consider is that disco volante sells a spoke wheel conversion for the yamaha fazer. The hubs are cnc milled aluminum and very light, but they are not cheap. This would solve your front end problem as you could adapt a whole fazer front end to your bike and get better forks and brakes in one swoop (you fit the front end by either have sanders machine make you custom triple trees or by replaceing the fazer stem with a cb750 stem in the fazer triple trees).
Another route you can go is to rob a dirt bike of it's front end but you will have to find a way to cut down the forks as they are probably too long. Most dirtbike fornt rims are 21", great for a chop but lousy for a biek you actually want to make turns. Try to find something in the 17"-19" range.
Personally I like modern rims because they take a tubeless tire, are easy to repair, and have a better selection of rubber.
Guys with later motors seem to have no problem fitting wider tires to the cb750. Usually they are restricted by the rim, swingarm, and frame and not so much the chain line. This is because the 77-78 bikes have a wider chain line than previous bikes. Guys building honda choppers have been able to get 180 tires on the back of rigids with minimal sprocket offsetting. I don't know if this has to do with the motor sprocket shaft being physically longer or just the sprockets being longer so you will need to do some research in this department. I think the largest a stock frame can hold is a 150 and that is if the rim, sprocket and swingarm issues have been addressed. As far as a spoke rim is concerned I would try using a supersport rear rim and brake disc just because cbr and cb750 axles are very close in size (if not the same diameter) and see if you can modify the cbr caliper to work with the stock supersport rear caliper mount (it might pay for you to find someone with a milling machine and maek you a custom bracket, also you could try getting a harely rear setup to work but the axle bore will need to be sleeved to fit).
A fast way to get semi-better brakes and an aluminum rim is to use a 75-77 goldwing front end on a cb750. It is a bolt on (if using temkin neck bearings you use one cb750 bearing and one gold wing bearing but I forget which one and where), will give you 37mm forks, true dual discs with a working speedo, and an aluminum rim. The down side is it is slightly heavier than your current front end and the brakes are still 70's brakes (which are meant to stop a heavier bike I might add so they do work fairly well) which means you won't be pulling any stoppies. I have this setup on my 76cb750F period cafe racer and I like it a lot but it isn't as cool as a modern set of nissen 4 pots on lightweight rotors.
The best advice I can give is find yourself a motorcycle junkyard you can visit reguarly. Bring beer. Bribe the owner with beer to let you wander around his place with a set of dial calipers. Either bring your bike or take detailed measurements of it (measurements from the centerline of the bike are crucial to finding wheels that fit, remember the centerline is constant). Wander around the yard measuring everything in sight. Sooner or later you will find something that works since there are a lot of standard sizes in motocycles (remember everything is metric so bring a metric caliper). Another thing to do is make friends with the guys at the service department of your local motorcycle dealers. So much so that they don't mind you taking measurements when ever they take a wheel off a bike.
A good way for you to figure out chain line on the fly is to measure from the centerline of the bike to the inside of the motorsprocket, then you measure from the centerline of any wheel you are looking at to the inside of the wheel sprocket. Since the centerline of the wheel will match up to the centerline of the bike, this will tell you whether your new wheel will get you close to ideal chain line or not. Any machine shop can make you spacers to fit any wheel to any swingarm, the crucial part is getting the sprockets close.
Personally I like the fzr400 parts because they are alloy, about the same size as most 70's japanese bike components (on my kawasaki h1 the pivot bolts were even the same size) and are not too expensive as compared with new r6 stuff. The fzr600 stuff is steel, but the same dimensions and even cheaper. I would use an fzr600 arm because it would be easier to modify (easier to weld steel than aluminum) and stronger, but it won't save you any weight. Fzr400s ran about a 140 tire to a 160 tire on a 3.5" rim, 600s use a 4" rim and run from 150 and up (and use different rear brakes). I hear ninja 250 and 500 parts are pretty good too so you might want to look into that as well. In other countries there are other 400 bikes that have trick pieces that a cb750 might use. Bikes like the zx400, cbr400, etc... that are pretty close dimensionally to a cb750 and never made it to N. America. You might want to locate an owners group overseas and ask for measurements from them, Shipping might be expensive but if it saves you fab work in the long run then it all washes out. A custom JMC swingarm will cost you about a grand pre-shipping, from UK, depending on options so figure if you can get something to work for cheaper than that you are doing good, on the otherhand a jmc swingarm is a bolt on and go deal (all the bracing you want, shock mounts, made to take any wheel you specify) so that may be the way to go if you have the ducketts and don't want to mess around with the leg work.
These are all things meant to give you some ideas, figuring stuff out for yourself is half the fun fo projets like these. There are plenty of guys who have done cbr wheel swaps to cb750s (some even using cbr swingarms and converting to monoshock) so ask around (and do a search through the site, there was a pretty cool F posted a few months ago with a cbr swing arm and front end).
If you want you can e-mail me at dean_morarity@yahoo.com and I'll try and help you out some more. In the mean time I'll look for those pics.
