I have a 1981 XS650SH that has a 19" spoke front wheel with dual disc brake and an 18" spoke rear wheel with drum brake. I want to convert to a rear disc set-up that uses a 19" front wheel, but I'm not sure what year wheel to look for. I believe there's a change in the hub around 1977 which uses a different offset and requires a different disc than post 1977. Can anyone clarify this for me? Also, does anyone have a wheel/hub that they want to sell?
In 1977 Yamaha made several changes to the front end. Fork tube OD went from 34 mm. to 35 mm. The early dual piston rigid caliper was changed for a single piston floating caliper, and the mounting points on the fork sliders were changed to fit the new caliper. And finally, the disc itself was changed from a 2-piece design to a 1-piece design that was more deeply dished. There was no change to the hub; spoked hubs from 1974 forward were the same, with the exception of the Heritage Special hub with its crazy high spoke count.
I wouldn't recommend using a stock front rim in your conversion; it's too narrow for use with any rear tire that you'd want to run. And yes, I know the style mavens run big fat 120/19 tires on those little skinny 1.85" rims, but it's a serious mistake. Another factor to consider is the rim type. The late Special II's used steel rims, anything from 1974-1979 used H-pattern alloy rims (AKA "dog pee catchers"). Locating decent 19" rear tires will be a problem.
The drum brake on the XS650 rear wheel is entirely adequate, and IMO the rear disc brake did little to nothing to improve performance. If you must have a 19" rear, you'll avoid more headaches than I'm in the mood to list if you install a 19" rim on your current rear wheel.
Last Edit: Mar 25, 2016 20:43:28 GMT -5 by grizld1
Thanks, your information is helpful. The reason I'd like to convert to a rear disc is purely for the "cool factor". My bike has the alloy shouldered wheels. If I could find a suitable rear disc type rear hub that I could lace to my existing 36 spoke 18" wheel, that would be awesome. However the only rear disc conversion I'm aware of uses a front wheel.
Do you know of anyone who's adapted a rotor to work with the rear drum hub? If the sprocket bolts went through the drum hub and attached to an adapter that fit inside the drum of the hub, the adapter could facilitate the attachment of a rotor. A spacer might be needed to replace the spacer used on the drum design, but it could conceivably work. I'm not a machinist or I'd take a stab at it myself.
Re. converting drum hub to disc, my guess is that you'd wind up with something ugly, very heavy,and probably dangerous, since braking loads would be applied out on the ends of some pretty long studs. You'd also need a disc large enough to allow the caliper to clear the edges of the drum; again, heavy and rather ugly.
If you just have to have a 19" rim and a disc brake in back, the easiest way to achieve it would be to lace a 2.15 or 2.50 x 19 rim to a front hub. I think I have a hub that I can part with; I'll send you a PM when I've looked.
I've read some blogs claiming that using a front hub on the rear is questionable. I'm not sure I agree with that. Braking loads are significantly greater for the front wheel. The rear wheel has to deal with the engine torque, the payload (including rider) and some braking. My current rear wheel is an 18" alloy "H" type. I may be able to lace a front hub to the existing rim which would suit me fine. It may require custom spokes to use the 18" rim so a 19" rim might be a better choice since I could use stock spokes. If you have a front hub you're willing to part with, I'd like to see it and talk to you about price. Hopefully, the hub you have is from a later (late '77 and newer) model because the offset and rotor attachment are different on the earlier models.
I know about the Omar's kit to make the front wheel work on the rear. Someone on this forum mentioned a guy by the name of Jim Henry who also does the adapted kits, but at a more reasonable price. The blog included his email so I sent him an note asking for price and availability, but never received a reply. Do you know this person and could you provide his current contact information?
Sorry, I don't know him; you might try a Google search. BTW, spoke hubs are exactly the same from 1974 forward; only the rotor itself changed, as a fast check of old part numbers will show you. However, the hub in question is from a 77.
Last Edit: Mar 28, 2016 16:01:50 GMT -5 by grizld1
r80rt: :)This is a splendid write up, THANK YOU!!!!
Dec 26, 2015 16:54:05 GMT -5
mashermoto: What the what is this shoutbox for? Or should I shout, WHAT THE WHAT IS THIS SHOUTBOX FOR!
May 12, 2016 22:22:21 GMT -5
motormike: Good Day ...just a FYI.. Wild Cat is this Labor Day weekend. Still go'n on. A few 650's still make the scene. Various rides at different skill levels each day.. awards dinner sunday eve. BS in the park'n lot after dinner.
Aug 23, 2016 7:57:01 GMT -5
lsettle: First post in over 6 years!
Aug 28, 2016 19:45:17 GMT -5
kardon: Wow quiet here, where did they all go.
Oct 7, 2016 2:18:13 GMT -5
gggGary: XS650.com LOL
Feb 16, 2017 20:49:02 GMT -5
buell88: Anybody have any idea who built the xs650 tracker used in the Draggin Jeans Ad on Pipeburn?
May 16, 2017 16:24:09 GMT -5
joshua: The regulator/rectifier unit I got from Mikes PMA has closer hole spacing than original. Are we supposed to mill the holes to fit?
Jun 7, 2017 19:25:58 GMT -5
joshua: My bad. I found the bracket they supplied to mount the rectifier/regulator... Uh oh. How is this meant to work? Which way is it meant to mount? Looks like I have to use some spacers or something. Good instructions would be nice.
Jun 7, 2017 22:09:52 GMT -5
craig8johnson: Not sure if this is the right spot or not but oh well...
Jul 11, 2017 18:04:15 GMT -5
craig8johnson: I'm checking the charging system. I'm afraid I might have fried the last battery. With the solid state regulator (after market) what should it be charging at. The book says, I think, 15 volts. I'm hitting 17 when revved. Is that too high?
Jul 11, 2017 18:06:19 GMT -5
gggGary: Yes 17 volts is too high, about 14 volts is max, sounds like you don't have the right regulator or it's wired wrong.
Jul 13, 2017 6:54:33 GMT -5
dean: Just saying Hello, new member who is going to fix up a 79 XS650 that has seen its better days. I will definitely have lots of questions coming up.
Jun 23, 2018 16:45:32 GMT -5
tt650: Trying to breathe life into a 1980 that's been stored (indoors) for 25 yrs. Air filters are dry rotted. Have cleaned carbs but she only runs briefly on choke then stops. Need jet setting info and other ideas that might help her idle and rev.
Jul 3, 2018 19:15:19 GMT -5
trix13: Hey everyone! New to the forum and am fighting those gremlins!! New charging system, ignition switch, coil and fuse box. Resistance is higher than normal on the ignition pick up so I'm trying to find one. No such luck yet.
Aug 16, 2018 8:50:48 GMT -5
trix13: Also, even though all of my connections are clean, I cannot seem to find out why , when at higher rpms, I hit the signals and the rpms pulse with the signals...hahah. same with the brake light. I appreciate all input!!
Aug 16, 2018 8:55:08 GMT -5
bob99: how do I post a question. I am new to the forum
Jun 6, 2019 10:52:10 GMT -5
adlpc: Hello all! Been enjoying your edifying posts and discussions - and as a fan of the XS650 since my early teenage years happy that I now own a 1980 Special which I plan to turn into a vintage half faired racer. Thank you all for being here!
Oct 1, 2019 0:58:56 GMT -5
jimothyj: Hello everyone, I just joined & wish would have known about this site in 2014 when I brought my 1974 TX650A back from the grave. I have spent a good deal of $$ and alot of time on it. Just painted it and working on electrical, I will post pics soon,
Apr 10, 2021 2:14:13 GMT -5
louisvan: trix13 - I had a problem with my 1975 SX650. When I got to highway speeds, the engine lost power. The problem was in the connectors. At a certain vibration and the wind pushing on the wiring loom, the connector lost continuity. A bad crimp to the wire.
May 20, 2021 1:19:09 GMT -5