2006 apex engine knocking

[seasonal]

Need help have a 2006 apex that had a knock in engine with good compresion and oil. After I took it apart the only thing we could find was the crank sprocket looked burnt and seemed a little sloppy against the reducer gear. Any Ideas?

 

[Sled Dog]

Reads like it may be the reducer gear bearing may have gone south.

 

[seasonal]

We checked the bearing it felt tight no play. There is a grove on the crank gear I am not sure if that is normal or not. Can you replace just the reducer bearing or do you have to repace the whole unit.