Nuts And Bolts
While changing an IO-520-BBs oil during an annual inspection, steel and red rubbery pieces were found in the filter. Metal determined to be coming from crankshaft gear driving alternator. Rubber was coming from alternator drive coupler. Four bolts holding crankshaft gear to crank were loose, allowing gear to slop around and cause wear of gears and coupler. Locking plates securing the four bolts were missing.