I got a free craftsman gt5000. It has a briggs ELS 725 26hp vtwin engine, model number 4467770244E1. PO said that it started blowing blue smoke. I got it home and noticed gas in oil changed oil installed new carburetor. I was turning it over by hand and I noticed a squealing sound at times on Compression? not sure. Before I put it back together should I check head gaskets? Anyone have any ideas Thanks