What kind of rear sprocket do I need?

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mconigliaro

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Hey guys, I just bought a pretty heavily customized xs650 with an unknown set of wheels. I took it to a local shop to have them look it over, and they told me it was time for a new chain and sprockets, but I'm not sure what kind of wheels these are, so I don't know what kind of rear sprocket I need. The guy who did most of the work on this bike is not the guy I bought it from (and I'm still trying to get in touch with the original owner), so you guys are pretty much my only hope for now.

For what it's worth, here's what I know:

The "H" model originally had a 19" spoke front wheel combined with a 16" spoke wheel in the rear. The rear was also a drum brake. Both wheels have been replaced with matching mags that have a 19" front and 18" rear..both discs.

Rear disc brake conversion is by no means plug and play. A disc brake swing arm with the brass bushing upgrade was installed instead of the stock nylon ones. This also helped the handling. Rear wheel had to be modified with conversion bearings and spacers to stay with the larger 20mm axle. Precise measurement and fitting to assure correct chainline and tracking also necessary. More spacing required for the disc brake. A lot of work but worth it to get rid of the 16" chopper rear. Calipers, master cylinder and other parts are stock Yamaha for ease of replacement if ever necessary.
Click to expand...

I'm hoping "other parts are stock Yamaha" means I can just go with a stock xs650 rear sprocket.

Thanks in advance!

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how many bolts hold on the rear sprocket ? if its four its most likely rd400 sprockets if six measure the distance between two diaganal bolts ans its 110mm its uses a 650 sprockets. As far as spront sprockets goes thats up to you wether you go 17 or 18t and 530 0r 520 but the length will be 104 link
 
yea rd wheel or xs400, ok its gonna be a little hard to find a 34 or lower rear sprocket. there should be a number stamp on the sprocket if not try try counting the teeth on the rear sprocket man its most likely gonna be 40, 37 or so teeth. the stock xs used 17t and 34t i like to go 17-30 or 18-32
 
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From the stock 17/34 one tooth on the front equals 2 teeth on the rear/ a 2-1 ratio. An 18/35 is a 1.94 - 1 ratio about the same as a 17/33. That's pretty close, a bit higher than stock but usable.
Leo
 
I looked as best I could on both sides of the sprocket, but I couldn't find a number anywhere on it. I did confirm it's a 34T though.
 
One thing that seems strange though, is that none of the rd400 or 650 sprockets I've seen online look anything like mine. There are four bolts on the outside of the sprocket, but in between those, there are another four holes with bolts that appear to only be accessible once the sprocket is removed (so technically, eight holes). You can see these pretty clearly in the pictures I posted. What's up with that? Should I care?
 
the other four might be for the cush drive ? im glad its 34 but idont where you can get another the front sprocket and chain are easy tho. sometimes you dont have to rplace the back but it is recommended, and yours look pretty worn. do some resarch man im sure you can find another sprocket
 
mconigliaro said:
One thing that seems strange though, is that none of the rd400 or 650 sprockets I've seen online look anything like mine. There are four bolts on the outside of the sprocket, but in between those, there are another four holes with bolts that appear to only be accessible once the sprocket is removed (so technically, eight holes). You can see these pretty clearly in the pictures I posted. What's up with that? Should I care?
Click to expand...

Hi mconigliaro,
other 4 holes different centers? Mebbe a generic meant to fit more than one bike?
Whatever, the extra holes reduce unsprung weight and that's a good thing, right?
If you simply CAN'T find a replacement; get a standard XS650 rear sprocket and have a local jobbing machine shop drill the 4-hole bolt ring in it.
If the hole in the middle is different the shop can either bore it out or make an adapter ring as appropriate.
Your bike's "look" suggests it would like to run 17/32 on a 530 o-ring chain.
(18T front lets the chain nibble at the shifter shaft. 520 chain wears quicker with very little weight saving)
and us belt & suspenders guys fit a Scottoiler, too.
 
Disc brake and spoke in the rear ?

I was asked elsewhere so ...

The rear caliper is bone stock 2F0 . I was careful to leave as much of the conversion stock as possible . With the un-modified KZ750B LTD M1 twin 18" disc brake hub and rim the Honda disc centers in the caliper once .200" is taken off the diameter . Now one caution , the disc was "marked" CB200C but I did not take it off myself so I won't swear to it . I'm told that the KZ305 is very similar also so ya pays yer money and takes yer chances . I did turn down one side of the rear hub and I believe it was the sprocket side so it would fit inside the center of a KZ650 sprocket. . As the project stands the disc is centered in the caliper and the sprockets are so nearly in alignment that I may be able to let it go . I did have to futz with spacers for hours but it fits . I should say almost fits . I'll have to pull the wheel toward the drive side about .250" to put it on center line but with all else falling into place I'm far beyond complaining. I had considered the modification of the front hub to carry sprocket and disc but going without the dampener was more than I or the gearbox and transmission could tolerate .

915081204.jpg


I've since laced a Borrani 18" valenced (shouldered) rim from a '70's Sportster and trued it in the swing arm so the offset is whatever it is but on frame centerline .

~kop
 
Hmm, I think I may have solved the mystery of the additional four holes in my current sprocket. From this thread: http://xs650temp.proboards.com/thread/11299

"It is almost impossible to use the XS650 sprocket for this project due to the six- hole mounting on the sprocket vs the four hole on the RD wheel. I suggest ordering a 32-34 aluminum sprocket from Sprocket Specialties . Just tell them you need the RD400 sprocket. When you get the new sprocket, you will have to drill four additional holes in it to allow mounting over the sprocket spacer nuts. These holes should be 3/4" to allow clearance for the nuts that hold the spacer to the wheel."
 
yup thats it man rd400 wheel and that explains the other four holes. i would go 520 tho man if youre already gonna get a custom sprocket from sprocket specialties or whereever, 520 chains are much cheaper. and that of them wearing out faster is false, new sports bikes run those chain and they make more power then our 650s ever will
 
I was never able to get anymore information from that thread. I did some research on some of Slide's older posts and got the information on the conversion.

Here is what i found + there is some info for converting a Special 19" front to a rear
 

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  • RD400 rear wheel conversion.pdf
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xs650dreamer said:
- - - 520 chains are much cheaper. and that of them wearing out faster is false, new sports bikes run those chain and they make more power then our 650s ever will
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Hi 'dreamer,
520 chain is 2/3rds the width of 530 chain and thus must last only 2/3rds as long.
As the cost is also 2/3rds you break even on chain BUT as you should also change the sprockets and they cost the same for both widths you lose money running 520 and you get your hands dirty more often.
The sportbike boys run 520 to save weight and so long as the chain lasts for the practice laps and a weekend's racing they are happy.
And if you look up the recommended maximum power transmission rate for industrial #50 chain, it's good for ~5HP.
It's amazing how far modern chain makers have come.
 
fredintoon said:
And if you look up the recommended maximum power transmission rate for industrial #50 chain, it's good for ~5HP.
It's amazing how far modern chain makers have come.
Click to expand...
Far enough that I was finally able to take the #630 chain off my 100HP !00 ft/lbs torque
Kowalski piglet (KZ1000P) and my GPZ ("little" more than 100/100) and replace it with modern #530 . I haven't tried anything less than #530 on an XS and probably wont . Modern #520 would be right at the limit of what the XS can produce .

~kop
 

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