The pilot of the tailwheel-equipped airplane reported that, during the landing roll, he felt a "tailwheel shimmy." He attempted to correct with elevator to no avail. The airplane veered to the right, he attempted to add left brake, but the airplane quickly ground looped to the right. The left wing struck the runway. He then taxied the airplane to the ramp with difficulty. Postaccident examination revealed that the left tailwheel steering spring was missing. He added that the spring was present and operating normally during preflight and taxi before takeoff. Crash fire rescue personnel found the left steering spring on the runway while conducting an examination for runaway damage. In pictures provided by the pilot, the spring appeared undamaged. The airplane sustained substantial damage to the left wing. The airport's automated weather observation station reported that, about 47 minutes before the accident, the wind was from 160° at 7 knots. The same automated station reported that, about 13 minutes after the accident, the wind was from 140° at 6 knots. The pilot landed the airplane on runway 27.