WR400 99 Blown Sprocket Bearing

Anyone else out there had a fully obliterated sprocket bearing go through motor. Our bike is a 1999 model approx 8000 kms, very well serviced running full synthetic oil its whole life and chain has never been overtightened. Our only related problem was when we first removed the original front sprocket at the age of two months we had troble even using a 3/4 inch impact wrench to remove the sprocket nut. Our only diagnosis is that from new the nut was so tight it may have crushed the inner race of the bearing inside and fractured it. The rest of the engine, not due to damage from the bearing is in perfect condition. We would like to hear from any other person/people that have had this problem to please respond to this letter.

Thankyou, Leigh


the chain tension will break the bearing. it can be very difficult to get the correct tension.

i lay on the seat & go for a bit of slack.


Leigh, perhaps while riding a small rock got inbetween the sprocket and chain, causing a momentary tight condition.

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