If the sleeves are in tight you might as well use a sponge rather than a block of wood. I use a heavy steel bar and a very heavy hammer. The engine in the picture had been set up for years. After the head, pan, front cover, the rear seal was removed and on blocks I had it looking like you see it in the picture in ten minutes. Less time if the sleeves are not stuck bad. I have never broke a block or even cracked many sleeves. To break a sleeve you have to put a shock with the sledge at an angle. That happens with splitting wood blocks or not being able to keep it straight up and down on the edge of the sleeve. With the longer steel bar you know if you cocked or straight when you pound with the sledge.