Ironhead rear wheel on cb750?

[bryantr]

Ok so I'm trying to get a plan together before I start building my bike. Wanting to use a hd ironhead rear wheel on my cb750 build.

First problem was the drive side is on the wrong side, will this matter as far as which way the drum brake lever is being pulled? If so can I mount it with the lever on top side of the drum?


Second problem the 51t sprocket on the ironhead wheel, will the 19t front sprocket cyclex sells be enough to correct the ratio?

Third problem is axle size the Harley is 17mm and the Honda is 20mm. I'm wanting a 2" extended swing arm, what would be the best route to accomplish this and have the 17mm axle mounts?


Lastly, the issue of the rear brake linkage. It would need a cable or jackshaft since the brake and lever are on opposite sides. I'd rather use a cable as I think it'd look cleaner. All helpful input would be greatly appreciated!

 

[bryantr]

I'm guessing not many people are interested in this idea because its taking a huge step back in performance? But I plan on installing new brake shoes and having the drum lined. I also plan on having a nice big drum brake up front and I have set up drum brakes before and know what to expect. Just doing this for aesthetic purposes. I should also mention I will no longer be referring to this as a cafe racer project, because...well it's not haha. Don't think I really want to limit it to a specific type or even sub-category of type of bike.


Mainly I just need advice on the gear ratio 19-51 for a CB750. Will be used mostly around town and weekend rides through the country.


As far as the swingarm I'm going to have my dad fab up a jig and have him make me a few. Shouldn't be too much trouble for him...he's been building race car chassis for years.


Also anyone have a vendor for custom length brake cables? Can't seem to find anything myself.




***edit: if no one responds this time I'll take the hint and shut up about it haha.

 

[VonYinzer]

Well, first off... Why? Whats wrong with the 16" Honda wheel? You should be able to push/pull the brake arm either way. at least you can on a Honda. Call MotionPro for custom cables. As far as the sprocket, you couls probobly have a custom one cut for very little money that matches the Honda tooth count.

 

[bryantr]

Why? Always really liked the look of having the chain and brake on the same side.. Purely aesthetic and I'm not building this to fit in or impress people. Just kinda have an image stuck in my head and really want to see it happen. If it sucks I'll change it haha. But you can't go any lower than a 51T sprocket on these wheels because the sprocket is on the outside of the drum.


Like the rear wheel on this bike.

 

[pacomotorstuff]

Bryan,
Regarding the ironhead brake / gearing thing, you can see how close the 19/51 is to your stock Honda gearing by division.
19/51 is .372.
Whatever your stocker is - and I'm just pulling 2 numbers out of the stone age here - say 16/45, the ratio is .356. Pretty close.
You also haven't said what rear tire you want to run - I've seen ironhead rear hubs laced up to 18", 19" and of course 16". Each tire has it's own diameter and it will affect gearing.
It seems you're right about one leading shoe and one trailing shoe brakes -it doesn't matter which way you rotate the brake shoe actuating cam - just make certain that if your brake has a dedicated leading shoe - and I think the ironhead does - have it in the correct location.
If you want to get real jammy, look on the web for instructions how to convert the sporty rear brake to double leading shoe brakes using factory parts, a little welding and a little machining. I'm eventually going to do this on one of my bikes.
It's probably lost in the mists of time, but I think at least one KR rider did something like that to his machine (basically the same brake as the ironhead) for mile dirt track and road racing.
Keep in mind that the Sporty hub has a smaller(!) rear axle than the 750 Honda and you may have get creative as to what chain pitch you use on your project bike to get everything to work.
If you can get the parts at a reasonable price, I'd say "go fer it". I think it'd look great and like you said, you're running a decent front brake anyway (4 leading shoe Suzuki?).
Pat.

 

[bryantr]

Pat,
Thanks for all the input! I like stance of the Wm gorilla punch CB750 and was wanting to go with 16" wheels and Firestone tires. Unfortunately between the gear ratio issue and the size of the front hub (I am wanting to use a Suzuki 4 leading hub) I don't know if it'll work. Have you seen them used with 16" rims? Looks like I've got some research to do. No worries I have plenty of time as I'm gonna have to save up around $4000 to build it how I want.
Bryant

 

[pacomotorstuff]

Regarding the use of 16" rims, you may still be able to buy a spoke kit to adapt a 16" to the Honda rear hub.
For the ironhead hub, it was a pretty common lashup - the 16" rim on a Sporty hub... may have even been offered by the factory for all I know and you may be able to find either of the above on ebay or someplace already complete.
The other thing you have to do is figure out wheel circumference, 16" (like you want to use a 5.10 or 130mm or something on the back, right?) versus the stock Honda 18" (which was probably a 120mm or something) and see how the 16 stacks up and how it affects your overall gearing...
Also keep in mind sprocket and chain alignment. I was told you could probably run about 1/8" or even a bit more wheel centerline misalignment as long as they are parallel to each other - in fact, the BMW R90 Superbike built in the '70's had a lot more offset for rear racing slick clearance, but the sprockets have to be damned straight and in line...
I've never seen a Suzuki 4LS brake on a 16" rim but I guess it can be done.
Another thing, those old Firestone tires with the "block" cross-section are pretty effin hard to ride on -maybe consider something else when you're closer to that part of your project.
Years ago, I saw a SOHC 750 motor in a late '60's Sportster frame, done up "Frisco-style". I have no idea how hard the swap was, but it looked real coooooooool.
Good luck with your project and keep at it.
Pat

 

[bryantr]

Thanks again Pat. I definitely have a lot to think about. I'll start a build thread soon.

 

[bryantr]

Ok, I'm leaning toward running 18" rims front and rear. For tires I really like the Firestone 450-18s. They match up diameter wise with the 130/90/18s so hopefully the gear ratio will work out. Going to look at a basket case this week...hope to get started soon!