2-split or not 2-split

Can anyone tell me if you have to split the cases to replace the bearings for the balance gear shaft on 2006 yzf450?

There is a bearing in each case half, and yes - they remove towards, and install from the inside.

There is a bearing in each case half, and yes - they remove towards, and install from the inside.
Wrong.

The bearings in the '06-'09 models are removed by driving them outward, and can be replaced with the engine in the frame, although it's a higher skilled operation in a couple ways, and should only be attempted if you consider yourself a fairly well qualified mechanic. This is how I did mine.

The bearings should be replaced in a particular sequence if done this way. Remove the weights and drive gears and the retainer plate on the right side bearing to start with. Understand this about the balancer shaft (refer to the picture on 4-87 of your manual):

  • The shaft should slip freely within the inner race of the bearing once the weights are off.
  • The shaft has a shoulder at each end that the bearing is clamped against when the nuts are tight.
  • The shaft has a flat cut on it, and the end of the shaft will only slide past the crank in one position.

You need two new nuts. Run the new one on the left end of the shaft, then run the old one down so that the shaft threads do not protrude through the nut. Tighten the new one out against the old one. This will protect the threads.

You will now need to drive the right bearing out by striking the balancer shaft on the left end. You may find that heating the case around the bearing pocket helps ease this process, or that striking the outer race several times sharply from the right side with a punch helps break it free. It will take a good sharp strike to initially dislodge the bearing, but afterward, it will move fairly easily.

As the bearing gets to be about half/two thirds out, you have to start checking the shaft alignment with the crank. You should be able to push in on the shaft and rotate it, and once it comes into contact with the crank, the position of the flat relative to the crank will become apparent. Be sure the flat is poised to clear the crank as you drive the shaft farther. It may also become necessary to remove the two nuts protecting the threads in order to run the shaft far enough to the right to remove the right bearing.

Once the right bearing is removed, you should find yourself able to extract the shaft outward to the right. At this point, you can remove the left side bearing retainer plate, and drive out the left bearing with a suitable tool by working through the crankcase bore from the right side.

The major risks are in damaging the shaft threads, and possibly damaging the crank, by driving the shaft into it because you failed to align the shaft for clearance.

However, it can indeed be done.

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