TOPIC:

I'm looking for some input on machining a cush drive/rear sprocket carrier.

I have done a swing arm swap on my KZ750 LTD and have had to move over the swing arm a bit to one side. I didn't want to do this but had to in order to get the sprockets close to lining up. The rear sprocket is still about 3/16" off center, even with a 5/8" offset front sprocket. Due to this, I have been looking at machining the rear sprocket carrier and looking for some advice from guys that have already sorted through this issue.

Thanks for all the help!

Is the wheel still central after moving the swing arm over ?
If it's not you will have to recentralise with new spacers and still take the original larger amount you had off the carrier.
On average it's usually around 8mm but i've had to remove more or less depending on wheel/motor.
I machine my carriers in the lathe but you could just take it to a machine shop and tell them how much you want off and it should be a simple job for them.
I set the carrier backwards in the chuck so I can take a very light cut off the back where it fits the cush to ensure it's parallel with the sprocket mount face then spin it round and machine what's needed off the sprocket mount.
Sometime it's more complicated if it leaves too little material for the sprocket studs to screw into and I've had to sink the carrier bearings and shorten the inner spacer to get the clearance required whilst still retaining a minimum thread depth for the sprocket studs.
I did a Z650 with Suzuki RF600 Teapot running gear a few years ago and it was a simple job with just a few mm off the carrier.
I'm doing ZX12R wheels in my latest Z1R Turbo project and the 6" wheels rear carrier has needed 15mm off , 7/8th front offset ( I've actually extended the gearbox output shaft to take a cheap stock sprocket rather than an expensive offset one ) and the frame notching but the wheel is still true central.

I offset a 900 with 3/8" front, then used an aluminum sprocket on rear. And another rear sprocket I cut just for a spacer 3/8" also.
This is a 150 x 16 hog wheel that is a 4" rim.
Then I countersunk the aluminum rear, used 45 degree flat head machine screws. This took away the stud and bolt sticking out. This gave me clearance at the swingarm, so I did not have to modify the the rear very much. Downside is an aluminum sprocket. But this bike is not a road bike.

Thanks for the help.

The wheel is not true center anymore, I had to offset it to get the rear sprocket close. It's been a bit difficult to determine true center because the wheel has a tire on it and I don't want to remove the tire.

I ran a straight edge straight across the tire, so it was meeting the sidewall in two places and ran that to the swing arm and marked it. I did this for each side to find the center of the tire. I then measured each side off the of frame at the axle point. The difference is 1/4", so to center it, I'd have to move it over 1/8".

The difference between the front and rear sprocket it currently 1/8" (3.175mm). If I move the swing arm over 1/8" to center it, that would leave me with having to take off 1/4" (6.35mm) off the carrier.

I need to order a 530 chain to make sure there is enough room between the sprocket and tire to take off the 6.35mm off the carrier. I'm assuming you would suggest centering the tire/wheel and taking off the larger amount of 6.35mm off the carrier. I mocked it up with a 630 chain and there is a total of 1/4" (6.35mm) of room between the tire and the chain, so with that, I suppose I could take 1/8" (3.175mm) off the carrier and move swing arm over little as well. That way there would be 1/8" between the chain and tire.

Zed- you mentioned the studs screw into the carrier. What is the easiest way to get them out for machining?

If you are doing it you need to do it correctly or not at all.
You cannot trust the tyre as an accurate datum for measurements as they can be off by a few mm on one side to the other compared to the rim.
Get the tyre off and center the wheel off the rim then you may find you have less to take off the carrier than you thought..
6mm is nothing and there will be plenty of depth left for the studs.
Use the 630 chain width for clearance , it's the same or fractionally wider than a 530 depending on make.
For the studs you either need a proper stud remover or lock two nuts together to unscrew them.
They are usually in with factory Loctite and it can be tough so a bit of heat on them may soften it.
Sometimes the studs get chewed up getting them out and most of the time i just fit new ones anyway as the old ones stand out like a sore thumb on a fresh build.

If you dont want to remove the tyre, you could clamp two straight edges either side of the tyre and check the measurements to the center line of the wheel (or to the rim). This should give you an idea of how centered your tyre is on the wheel. Rotate the wheel and try it in a few different positions to be sure.
To get the rear wheel in line with the front,run two longer straight edges from either side of the rear tyre up along front tyre. Again,measure either side and adjust til you have it where you want.
(You just need to clamp enough for the straight edges to hold. Dont over tighten the clamps or you might distort the tyre and the measurements.)
Some people reckon the rear wheel dosnt need to be in line with the front. I find this crazy and wouldnt trust a bike with wheels running on different lines.

P.S. I tried a ZXR 400 wheel on my project and there wasnt enough meat on the cush drive to shave off. So, I went with a 600 Bandit wheel in the end and I had a machinist shave off about 10mm + - . Still solid. From what I remember the studs just pushed out the back.

Beware;

davido wrote: Some people reckon the rear wheel dosnt need to be in line with the front. I find this crazy and wouldnt trust a bike with wheels running on different lines.

Some of the folks who say that are factory engineers. The Kawasaki ZRX 1200 comes from the factory with an offset rear wheel, as do a number of HD models.

Cant speak for the ZXR but holding up HD as an example is just asking for trouble!! and Im sure factory engineers are working on the grounded Boeing 737 fleet as we speak .
Why would you want to do that anyway? A bit of thought and you should be able to line up the wheels and have the clearance you need for the chain run. Shaved cush drives are only one part of it. Offset front sprocket,scalloped frame. I managed a 160 tyre (on a centered wheel) with a shaved cush drive,offset front sprocket and a change of chain thickness. Other people have fitted 170 and 180 tyres. Look at the frame scalloping the AC sanctuary boys do. Top of the line bike builds. I doubt they would go to all that trouble if they could just shove the wheel over to the side a bit
Then again Im no engineer. What do I know!

This is my latest effort for a 6" rim.
If your gonna do it, do it right.

I know that frame notching is common, but I wonder how much strength is lost in the process?

Thats living on the edge right there