1986 Ski-Doo Factory Shop Manual, Page 254Get this manual
Section 03 TRANSMISSION Sub-section 02 (DRIVE BELT)
9Sheared cogs, compression section fracture or tornCAUSE
a) Refer to Installation sectionb) Check drive componentsc)
a) Improper belt installationbl Belt rubbing stationary ob ject on pulleysc) Violent engagement of drive pulley