On Thursday, August 26, 1993, at 0915 eastern daylight time, a Piper PA-25-235, N9556P, registered to Spraying Specialists, Inc., and piloted by Peter A. Cummings, sustained substantial damage during a forced landing in Chesapeake, Virginia. the pilot was not injured. Visual meteorological conditions prevailed, and no flight plan was filed. The flight was being conducted under 14 CFR 137. The pilot was conducting a spraying flight. In his report, the pilot stated: Engine failure occurred while making final alignment for normal aerial application swath. An emergency landing was conducted in the field being sprayed. the airplane flipped over...because of the dense foliage of the crop. Mr. Fred E. Teator, Air Safety Inspector (Airworthiness) for the Federal Aviation Administration, conducted an examination of the engine. In his report, Mr. Teator stated: Prop was virtually undamaged...The engine was removed from the aircraft, after it was determined that the engine was difficult to rotate, indicating an internal problem...External appearance of the engine showed nothing unusual. Accessories were removed with nothing to note. When the crankcase pan was removed there were four broken teeth found. The gear case cover when removed showed the crankshaft gear to be loose and the alignment pin and attachment bolt were sheared. Crankshaft gear and magneto drive gear had 10 teeth broken off. There was no indication that maintenance (or lack of) caused the engine stoppage. Consensus of opinion is that the engine stopped after the crankshaft gear bolt and guidepin sheared. There was no other obvious internal engine damage and the engine rotated freely when the damaged gear was removed. The cause of the bolt and pin shearing cannot be determined.