What happened
During an approach to a field, the engine began running roughly, causing smoke to fill the cockpit. This smoke limited the pilot's forward visibility while performing the downwind approach. As the aircraft reached short final, the pilot identified a fence positioned across the landing area and responded by pulling the yoke all the way back.
The resulting hard landing caused the airplane to travel through the fence. The impact led to the collapse of the nose gear and caused damage to the wings and engine fuselage.
The investigation
Mechanical examination of the engine revealed oil present on the engine cowling and near the #4 cylinder. The oil sump contained approximately 1.5 quarts of oil. Investigators found that the push rod tube and the exhaust valve push rod on the #4 cylinder were bent and had been displaced from their positions.
Records indicated that the engine had flown 697.65 hours since its last major overhaul, and the aircraft had flown 26 hours since its most recent annual inspection.