My front sprocket "wobbles"

Many people are taken aback when they receive their replacement front sprocket and it seems to “wobble”. This sprocket design is known as a floating sprocket and is perfectly normal.

The bolt-on plate that secures the sprocket allows just a tiny, insignificant amount of sideplay to the sprocket. There is nothing whatsoever wrong with this design, and the sprocket will run forever like this and never, ever cause the slightest amount of trouble in any way, shape or form.

In fact, this is a superior form of sprocket mounting because it is simple to install and remove in a few seconds without any special pullers. The earlier traditional mounting was with splines inside the sprocket and splines on the gearbox shaft, and a big nut threaded on the end of the shaft supposedly locking the sprocket. What ALWAYS happened was that the constant reversal of stress on the chain would wear the splines on both sprocket and chain (there had to be enough original clearance for you to push the sprocket on the shaft, or if actually tight, you might have to bash it on and would need a puller to get it off), the result being that the parts would develop a little clearance, and tend to loosen whatever form of nut they had in the design (maybe some form of locking nut like a "Nylock" with an insert). So, the locking nut would stay in place, but the sprocket and shaft splines would rock back and forth against each other. Just like the sprocket and splines do on our 250 Ninja.

The advantage of our design is that it takes less space at the end of the shaft than does the older design with a nut. Besides, if the big nut did manage to come completely off with the old design, the whole thing might manage to get unshipped and raise hell.

Also, there is logic to having a gear floating on a shaft (within certain limits).

The rear sprocket is roughly fixed to the rear wheel, and even with very careful and accurate alignment, there is probably always going to be some degree of mis-alignment. Allowing the front sprocket to float and even potentially tilt a bit on the shaft actually takes stress OFF the chain, and places more of it onto the shaft/sprocket union. This is advantageous since the sprocket and sprocket shaft are both MUCH stronger than the chain itself.

If the rear wheel is slightly to one side or the other of the ideal plane of chain travel, the front sprocket can float perhaps enough to create a different ideal path, or at least enough to reduce the side-to-side stress that may be placed on the chain. If the front and rear sprockets are not perfectly co-planar, allowing the front sprocket to tilt slightly will allow the chain tension to align the sprockets in an inclined plane, again, taking twisting tension off the chain, but now placing it on the sprocket-shaft union.

In this situation, the natural tension on the chain will shift the front countershaft sprocket into better alignment. This is not a good substitute for aligning your chain, so you should make sure that is done periodically.

Sprockets are parts that wear slowly but constantly, and have to be changed periodically. Be happy that your 250 Ninja, like most Japanese bikes, has the ideal form of front sprocket mounting.

A note on design: The cheaper sprockets are cut/stamped out of a flat piece of metal; they're the same thickness all over, like a rear sprocket. The better ones (OEM and AFAM, perhaps others which we're not sure about) have a thicker area in the center where the splines are (the "hub"). This makes them marginally less wobbly, and should reduce wear on the countershaft splines, since they have a larger contact area.