Time for a new top end, or new engine. If you do top end only you need to flush the case thoroughly. Remove the magnet from the magneto side cause it magnetizes the crank weights so metal sticks to them, and is hard to flush out. I pull the engine, flush 2 with gas. Then flush upside down with pressure nozzle on garden hose. Blow it out. flush with oil fuel mix. then rebuild. Before removing engine bring rod up till crank is at TDC and hold weight with fingers. Try to move the rod up and down while holding weights from spinning. If the rod moves and you detect play in the rod to crank bearing it's new engine time.