I bought a wrecked airplane (RV6A) that only had 6.9 hrs on it. The engine was brand new from Lycoming (Vans), but when it was wrecked the prop did hit the mud as the plane wrecked in the rain. The prop was barely bent and repaired. I decided to pull the back engine cover and check the dowel pin on the crank gear in addition to doing a crank shaft starightness test. (put a dial indicator on the crank snout and slowly roll the engine) Everything checked out perfect, so I am putting it back together. Installed new bolt and retaining ring on the crank gear, per Lycoming recommendations.