I am having problems with bearing carrier on my 400ex. Every time get some were the quad is pulling real hard the bearing carrier turn whitch losens the chain. The bolt are tight too. Im getting tied of every time I go riding having to stop and tighten the chain back up. How could I get the bearing carrier to quit turning.

 

Throw the stock bolts in the trash. I use normal bolts in mine, works alot better.

 

This is a classic sign of shot bearings! Don't ride the bike again, until you replace the bearings. Otherwise, you will ruin the carrier as well (like I did) and be in for a big $$$$ replacement!!!