FZ600 Swingarm

FZ600 Swingarm

1985 RZ350

Measuring & Installing the Offset Sprocket

This page assumes you already have the FZ600 rear end in the bike and the rear wheel mounted. Since the rear sprocket carrier will now be out of line with the original front sprocket it is important to get a measurement of how far out of alignment they are in order to get the offset correct.

The first step is to make sure the wheels are aligned with each other. Since the rear wheel adjustments basically push the wheel to the left or to the right, it is important to make sure that both sprockets are parallel to each other.

The basic idea is explained here, but it involves using two strings with weights at the front wheel end and measuring the distance to the front tire when the string just touches the side of the rear tire.

In practice I found an 8' level was a much better way of determining when I was parallel with the rear wheel, especially with a brand new tire. I balanced the level on some cans and could easily determine when it was touching both the front and rear edges of the rear tires, and then measure the distance to the front and rear edges of the front tire.

Once the wheels were aligned, I carefully clamped s amll extruded tube on the outside face of the rear sprocket. The picture above shows it on the inside face because I forgot to take a picture on the outisde, so be sure to use the same face of each sprocket in your measurements. Also be sure to clamp the tubes just tight enough to hold it in position but not any tighter.

I then did the same thing with the original front sprocket.....

I was then able to get the two tubes to cross over and I could measure the difference between the ends which worked out to be 7.8mm. I double checked this figure by adding all the widths of the various rear wheel components together of the original RZ and the new milled down set up and agreed witihn 0.2mm so it is good enough for me.

The problem was that the suppliers I talked to only make offsets front sprockets in 1/8" increments. 1/4" was too little, and 3/8" was too much. I noticed when I removed the original sprocket there is a collar that rides against the oil seal, and I realized that I could get the 3/8" (which is 9.5mm) sprocket and machine down the collar by 1.7mm instead to get to my desired measurement.

Once again, JP Morgen took on the work, and above is the shot of the collar after it was machined down. There is a limit to how much you can machine it down because the splines of the output shaft will stick out too far beyond the face of the sprocket...but it turns out that 1.7mm was so little to remove it didn't affect the sprocket and the sprocket nut has a recessed groove in it to accommodate some play.

The new offset sprocket can then be installed along with the lock washer and the nut, and then bend the lock washer over the nut to stop it from turning.

The final shot showing the rear wheel mounted, aligned, and ready for the road.

Next Section -->