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Discussion Starter #1
I have a thread going on over at the Hinckley classics forum but I thought I would post in a more appropriate place. I am doing a somewhat common ZRX rear wheel swap on my Thunderbird. The problem that I am running into is that the ZRX sprocket is about 1/8 in closer to the center of the hub than stock. My question is how I should go about safely spacing the rear sprocket? I have looked at place a washer under the sprocket however there is a machined lip on the hub that the sprocket sits in that would no longer contact the sprocket. What would be the idea process be to get the correct chain line?
 

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I had a look at various motorcycle sprockets around the garage to get some idea about what you are describing. As you probably guessed, the ring keeps the sprocket from moving out of position as in out of round. that would wear your chain out in no time.

While it is true the bolts hold the sprocket on, they really only keep them in place against the flat part and from spinning on the hub; the bolt and hole are not so closely machined nor sufficiently strong to prevent some wobble without the ridge.

What to do... I have a metal lathe; what i would be tempted to do is make a spacer and bolt the sprocket to that. Easiest would be to make one from an aluminum sprocket so it already fits that groove just right. turn on lathe, even a wood lathe can turn aluminum, and cut off all the teeth. If it is too thick for the amount you need to move the sprocket, that will take a metal lathe or disk brake lathe to thin it. Decide where you are going to want to install button head screws and mark the spacer with a scribe while it is still on the lathe. would figure some way to be sure the two openings line up just right; my first thought, locater pins, hardened steel pins. 1/4" would be fine; then the ream you need to buy will be cheap. You clamp the pieces together, then slightly under drill the two pieces together, , then use a 1/4" ream for a perfect hole. insert the pin. Check that the sprocket and spacer are still perfectly aligned, then drill and install another one on the opposite side. No need to get carried away and put loads of these in, you're going to remove them after getting everything bolted together.

Use a compass to mark each spot along the previously scribed circle to drill and bolt the assembly together. i would think 8 or so would be fine, more is fine, too. Just divide the circumference by 8 and that is how far apart they need to be. Pi r squared using the radius of the scribed circle. Carefully centerpunch each location. Using a drill press, drill a smaller locater hole; its easier to see that you are on the mark though a little out of round here won't cause harm. Then use a #3 drill which is the tap drill size for 1/4 28. separate the sprocket and spacer, then drill the spacer holes out to just shy of 1/4" then finish the holes with the ream. using a 1/4 28 tap and tapping fluid, tap each of the sprocket holes. Now you need to determine the length bolts needed. Presuming you use a flange nut that has a rim on it, you'll need just enough bolt coming through for the nut to have all its threads against the bolt. NOW you buy the nuts and bolts; I would use 1/4 / 28 #8 hardness button head bolts and flange nuts. clean all the mating surfaces, dry assemble everything to see it fits. , then mount the wheel on the bike and double check that everything is right. If it is, you can use Locktight red on the bolt threads. You could also use some similar locking material between the two plates. loosely assemble all of it, then torque the screws remembering that the bolt is #8 but the sprocket is a softer steel. Then mount the nuts. here you can tighten them down according to torque specs for that size #8 nut/bolt.

OK, there are other way. I was just running with it. You already know I chose to move the wheel further left to get the sprockets lined up straight.
 

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(SNIP)...
. You already know I chose to move the wheel further left to get the sprockets lined up straight.
I didn't move the Kaw ninja wheel far enough to the left to line up the sprockets properly. Noticed the sprocket wear while changing a flat tire.


The lip I'm hacking at normally holds a seal to keep out debris. I'm not sure if I'll be able to use the stock seal.

a previous poster was pursuing using spacers to move the sprocket further left, an idea I was avoiding since it looked like it wasn't necessary. If my latest adjustment doesn't work, I'll be looking at that option.



 

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Discussion Starter #4
toller,

These are very interesting pictures, and I really appreciate all the feedback that you have added to these posts. I will be interested to see if you feel any effect from moving the rear wheel further to the left. How many miles do you have on the swap? Also do you have the stock front end or did you do a zrx fork and wheel swap?

I am on the verge of wrapping up my swap, I finished torquing everything down today and all I need are those bolts that attach the brake line to the torque arm. Nothing a quick run to the hardware store won't fix, but the test ride will have to be between rain showers tomorrow.
 

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toller,
(snip) How many miles do you have on the swap? Also do you have the stock front end or did you do a zrx fork and wheel swap?
(Snip)
I have somewhere between 10,000 and 15,000 on the rear end perhaps 4,000 on the front. I did swap the front wheel and fork tubes. I bought the forks separate from the wheel; big mistake. Ended up with the wrong front wheel and had to make my own axle 25mm diameter instead of the typical stepped axle that is 20mm through the wheel bearings and 25mm in the cinch mounts on the fork lowers. I strongly recommend anyone buying the tubes, wheel and brakes/calipers/rotors as one, though this package deal might boost the price. I actually only used the fork lowers and internals because the stock kawasaki tubes are too short. If you're lucky enough to have a thunderbird sport, all ya need is to swap the wheel for the same end result. I had to make my own caliper mounts, too, which can be a pain.

Like you, I'm not much on the road this week, temperature is in the teens and single digits.

Oh yeah, great deal on Dunlop D205 180/55 17" tires at Tires Unlimited for 75.00 plus shipping. I bought two pairs since i normally go through 2 or 3 rear tires a year.
http://www.tiresunlimited.com/ALL%20TIRES/Dunlop/dunlop_d205.htm
 
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