what sprocket do i need ( rear rim question)

[mitchberry]

i guess there's a small chance that anyone would know this off the top of their head.. but...

the kid i bought my bike from found a bunch of random parts from craigslist during the time he owned the bike.. one of things he found was a good rear wheel.  the one that came ON the bike was a 16" rim (78 cb750K) every one of the spokes were rusted to crap and should be considered to be unsafe, so, he found another rim on CL to replace it with in much better (damned near perfect) condition...   the thing is that it is an 18" rim  (fits a 110/90X18 tire).. it is obviously off of a different year bike.. it may have even been off of a different type of bike altogether, but i assume it was a cb750 of some year.

the plate that holds the shoes on it was slightly different from the stock one, and the rose shaft that came out of it was considerably smaller than the stock one (therefore i couldn't use the same lever on the new one as i had on the old one)

given that, i retrofitted the factory "plate" as we'll call it, to fit that rim by adding a washer inside the hub, and shaving about an inch off of the wheel spacer.. it fits perfectly, and works flawlessly, just as it should..

 MY QUESTION though is this..

 the sprocket that's on it is a small sprocket... he had a larger sprocket that came with the bike when he got it...

 he had it backwards and thought that a smaller rear sprocket would give it torque, so he went with that as opposed to the larger one that was on it..

 honestly, i want MORE torque and less top speed. i PROBABLY won't be taking this bike past 90mph at any given time, but i would like to be able to get there a lot quicker.. so... i need a 45 tooth sprocket in the rear at least...

ok.. the question....

 WHAT YEAR / MODEL cb750 came with an 18" spoke rim ????  as opposed to the 16" spoke rim..

 the reason i ask is because, i went to change the sprockets out and the larger sprocket i have does not fit the new rim...

 i have NO IDEA what year the rim is from, or how to find that info, or which sprocket will fit it..

 i can buy a new sprocket no problem, but it's about a 50/50 chance that i'll buy the wrong one and it wont fit..

this is kind of important to know asap, because, i need to buy a chain to get this thing going, and BOTH of the rear sprockets i have are used... and i only have 1 front sprocket, also used...

 the front sprocket is easy enough to figure out.. it's the stock motor...   but i am having difficulty figuring out which rear sprocket to buy...  

and then there's the fact that i have no idea what chain length i'd need for that...  i think the standard chain size is 80 links  on a 630...

is it possible to anyone's knowledge to do a 530 conversion?  there's REALLY no need for that heavy of a chain on that bike...

 sure their fast, but they aren't -that- powerful... my busa doesn't even have a 630 chain on it i don't think... abd that's just shy of 170 horses... double what the cb puts out...  

a 530 chain / sprocket setup would shave a lot of weight off of the beast...

then again, mayyybe the sprocket that is on the rear IS a 530..... and the front one is a 630.. i really have no idea at this point..

That's the thing about buying a project that several people have worked on and failed with.. you have no idea what they've done..  i would ask the kid these questions but he's pretty clueless about bikes.. which is why he sold it to me in the first place.


 any thoughts??? seasoned advice is much welcomed

[Re-run]

Well none of the sohc CBs came with a 16. that is a harley rim conversion to take advantage of the tire choices in that size. the 77/78 cb came with a 17 inch spoke rim for the K and the comstars were 18 I think. Prior to 77, every was a 18 inch rim which was narrower. So the rim you have may be from a 69-76 cb but I dont think there are any defining marks to make sure.

For more torque, you would want a smaller front sprocket or a larger rear. Do not go below a 16T though on front and remember, a 1 tooth change on the front works to about a 3 tooth on the rear.

When I did a 530 conversion on my 78k, I got a 112 link chain and took off something like 4 full links. I cant remember if I got sunstar or jt sprockets though. You will want to look at your spline, if I remember correctly, it is a 6 tooth spline so you need to make sure the sprockets you get are the same. fYI, the stock 630 chain was 88 link. back in the day, metallurgy was not as good and the cb was snapping 530 chains and knocking holes in cases, thus the 630 chain. These days, a 520 works fine.

You would not be able to use a 530 with 630 though. teeth are spaced differently.

[mitchberry]

actually, upon closer inspection, you're right.. it was actually a 17" rim not a 16 as i mentioned earlier...

the front sprocket is a 17T which i expect is probably the stock one... or at least the stock size...   i don't know if i need to go much smaller than that.... i would never do a 15t on a bike this heavy, or with that high of a torque:weight ratio..    but a 16 sounds good.

The sprocket he put on the rear is a 37T... rather, that's what came on the rim he got to replace the bad rear wheel...

There is a 45T sprocket sitting there that was on the original / junk rim but it doesn't fit the "new" rim... that's the problem i'm having... not sure what to get... i hate having to send stuff back to our distributors.. they charge re-stocking fees and such..

so i guess what you're saying is that every cb750 in existence prior to 77 had the same rim, then they changed it in 77 and kept it for 78, which is what i had on my bike stock...

and yeah, i would definitely assume that it's an older rim... just.. in better shape..  

 the only other thing i'm worried about though is the chain.. i can't find any markings on the chain to indicate that it IS in fact a 630 chain.. i kinda assume it is because it's huuuuuuge ..

so i guess the other thing is, if i do the conversion, that makes it even more difficult to figure out which sprockets to get....  

But i do like the prospect of losing about 4 pounds on the chain alone.. lol

i dunno.... i could always re-drill the holes on the 45T sprocket and use it, but it's a used sprocket...  if i'm going to put a new chain on it, i won't do anything but put new sprockets on it...

any idea how to figure out for SURE that it's actually a 630 chain?

[Re-run]

Well on the 77/78, the stock chain was 630 of course. the front sprocket was a 15tooth and the rear, 41 for a 2.73 ratio.
In the 530 equivalent, a 17t front and 47t rear give a 2.76, so slightly more bottom end but hard to notice.
If you did a 16/47 you get a 2.93 which would be a fair jump in bottom end pull.

the difference in 630 is apparent on the spacing between rollers. So if you have a known 530 sprocket, if the teeth fit, it is already a 530. Although it sometimes says the size on the sprockets too.

I would not worry about the chain though if it is old. Sprockets/chains are best replaced together and then if well lubed and cleaned, will last 10,000+ miles, some people can even get 20,000.

[mitchberry]

well, i want to convert to a 530 to reduce the weight just a little... sure its only a pound or two, but every pound counts...    as for the sprockets, they all fit the chain, and none of the above are market with a size, one is a sunstar or whatever and only says the teeth which i mentioned in the last post..

 as for chains and sprockets, i know that you replace them all together... they all wear together so need to be replaced together.  

with that said, the larger sprocket came used from a different bike and doesn't fit my rim...   the one that's on the rim now is also used and came with that rim... the original one for the bike was lost or thrown away and... old anyway.. the front sprocket is original to the bike most likely, so is the chain, which, the kid did a poor job of taking off, and he claims it was messed up in the first place which is why he cut it.. he couldn't get the tool off of it, so it's hanging there, the chain is unusable.   so i have to replace that, and may as well replace the sprockets since it's against my religion to put used sprockets...

hmm.. i'll call one of our distributors tomorrow and see if they can find me a part number for the crap i need..  easiest way. lol

[Lucky 1]

Well it is a year later and I have the same problem.
But since you never posted your solution I guess I will have to
start all over.

I did find a place that sells the sprocket set for the cb750 (my year 78)
http://yamatoyamotorsports.3dcartstores.com/Parts-Unlimited-Front-Sprocket--530-Conversion--Honda-CB750-69-70_p_1852.html
The website shows a front and rear sprocket.
The rear sprocket is steel and has a design that has a lot of the weight removed.
Only thing is the sprocket size on the rear is 34 teeth and the the front is offered as 17 or 18 teeth.
STOCK for my bike is 15-41=2.73:1
So 18-34 is 2.0:1 much higher.
Question is will it be too high??

I guess since the chain is smaller a larger sprocket will fit in the front.
The price is only $18 for the set?? Wow.
I have to call tomorrow and find out more on the telephone.

[Rodgil]

I went from 18/46 to 18/40 on my 1982 CB750FZ DOHC, 1st gear is now like second, 4th gear is like 5th.
I wouldn't want to go any higher than my 2.22 gearing.

[Lucky 1]

The stock rim on the 1978K model was 17 inch.

I found the #520 sprocket for the front of my 1978 CB750K 17 teeth.
I am now looking for a rear alloy sprocket 45 teeth.