98 yz400 excessive engine noise?

I have a 98 yz 400 and it seems to make excessive engine noise. the shop said that these bike are notorious for the main drive gear coming loose. anyone experience the same?

The 98 YZ got this loud engine noise i think its normal...try a Petrol with higher oktans, will help the motor "pinging" less. I fill only 98 oktan in my Yammi, engine becomes much more quieter since then...

You want to check the primary drive gear for sure. The balancer drive comes loose. What happens is the key way deteriorates and allows the balancer to run slightly amuck. My suggestion would be to make your own keyway, as the Yamaha keys are too short, or could be longer, whatever your view is. Usually its a modle year 2000 issue, but the earlier bikes had the same crank. You'll need a 30mm socket to get the clutch hub off and to tighten or replace the primary drive gear also. Advise on the socket, go to pepboys. Sears wants an arm and a leg for it.

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