I am debating about filling my block. For those that don't remember, my motor will be a competition piece. I was not planning to run water anyway. A friend bought a couple of these motors when he was building his competition motor (post 1777 for photo). Several were cracked at the front of #1 cylinder and the front web. He believes this is the week spot in these engines. He filled his block. I am wondering if this is where they break if they freeze, but not a strength issue during operation?? Recently another guy using one stuck #4 rod out the side. He destroyed everything inside. That wasn't caused by block issues but a rod issue. I had an extra block for him but he is still needing a crank. If I decide to fill the block I am wondering what to use. The common block fill material has iron filler in it. That makes sense for an iron block, but not so much for an aluminum block. I have that here in bulk. The other option is epoxy with aluminum in it. That gets very expensive if it is purchased premixed. Epoxy is about $5 a pound if you buy bulk. Aluminum powder is cheap when purchased by the pound. My wild guess is epoxy weighs about 10# a gallon. Another option for the aluminum is waste from a machine shop. I have access to all of the aluminum milling chips I want. I would need to clean the coolant residue from them. Anyone have suggestions?