The aircraft was in normal cruising flight when the propeller suddenly went to fine pitch. A check of the instruments showed that the engine oil pressure gauge as reading low. The pilot immediately altered course in an attempt to reach a nearby airstrip. However, the engine then seized completely and the pilot was forced to carry out an emergency landing on a roadway. During the landing roll the right wing hit a tree, slewing the aircraft off the road and into a ditch. A subsequent inspection revealed that the external line which carries oil to the propeller governor had burst. It was found that this pipe had for some time been chafing against a clamp which secured another oil line.