DURING CRUISE FLIGHT AT 3500 FEET, THE AIRCRAFT YAWED VIOLENTLY LEFT, FOLLOWED BY AN ENGINE SHUTDOWN. THE PILOT ATTEMPTED A INFLIGHT ENGINE RESTART WITHOUT SUCCESS. LANDING WAS MADE TO A PASTURE WITH THE GEAR UP DUE TO THE SUSPECTED WET GROUND CONDITIONS. DURING THE GROUND RUN, THE AIRCRAFT STRUCK A FENCE ROW, RESULTING IN SUBSTANTIAL DAMAGE. THE VIOLENT YAW AND ENGINE SHUTDOWN WAS THE RESULT OF THE TAPPET FACE FAILURES. EXAMINATION OF THE FACES DID NOT DETERMINE THE FAILURE MODE.