On February 26, 2013, about 0930 mountain standard time, an experimental Blumer (Quad City) Challenger II, N107BW, collided with a sign during an off field landing on a road near Peoria, Arizona. The pilot/owner was operating the airplane under the provisions of 14 Code of Federal Regulations (CFR) Part 91. The private pilot and one passenger were not injured; the airplane sustained substantial damage. The local personal flight departed Pleasant Valley Airport in Peoria about 0910. Visual meteorological conditions prevailed, and no flight plan had been filed. The pilot reported that he was practicing touch-and-go landings. On the base leg, the engine lost power, and he decided to land on a dirt road. He landed uneventfully, but a wing collided with a road sign during the landing roll. The airplane spun off the road into desert terrain, and sustained substantial damage to the wing and fuselage. The engine was a Rotax 503, serial number 4298279. A Federal Aviation Administration (FAA) inspector oversaw examination of the engine. He discovered a cracked cooling fan housing that he believed resulted in misalignment of the magnets in the ignition system, and thus an ignition failure and loss of engine power. The fan housing was not a Rotax part. No Service Difficulty Reports (SDR) were found on file with the FAA regarding the cooling fan.