I just use a hammer and chisel, and split the chunks into 2-3 ounce pieces for longer smokes, and smaller pieces for shorter smokes like chicken or fish, so I end up with 2 or 3 chunks per smoke, rather than a single big chunk. It's no problem, and well worth the trouble considering the quality of the wood compared to other wood sources.
Were you using a chip screen or foil in the bottom of the smoke box? You should not be with wood chunks. Also, you might want to experiment with where you place your wood, front middle or back, over the holes or between the holes.