On August 13, 1994, approximately 0805 hours Pacific daylight time (PDT), a Piper PA-28-140, N95285, registered to and being flown by Gerald A. Coon, a certificated commercial pilot, was substantially damaged upon collision with an irrigation system during the landing roll following a power loss and forced landing near Redmond, Washington. The pilot and two passengers were uninjured. Visual meteorological conditions existed at the time and no flight plan had been filed. The flight, which was personal in nature, was to have been operated in accordance with the requirements set forth in 14CFR91, and originated from the Auburn Municipal Airport, Auburn, Washington. The aircraft was destined for Abbotsford, British Columbia. The pilot reported that while cruising at 2900 feet and slightly east of Sand Point, Washington, an engine vibration and loss of power developed. The pilot chose to execute a forced landing in an agricultural field. During the landing rollout on dew covered grass the aircraft's right wing impacted the irrigation system. After the airplane was retrieved from the field, an engine examination revealed that part of the number three cylinder exhaust valve was missing. Extensive damage to the cylinder wall was also noted.