You may of heard at some point in time the term 4 bolt main engine , so what exactly is it ? Some of you know , but for those who never seen one or know what to look for hunting at a swap meet here are some pics that give you a shot of what to look for. This is a 350 cube Chevy engine 1974 vintage. This is a bare block, but you can see 5 main bearing caps that would hold the crankshaft in place. If you look at the center 3 caps they have 4 bolts holding the cap down, the outside 2 caps have 2 bolts. If this was just the common 2 bolt main block then all 5 caps would have only 2 bolts each. But the stronger 4 bolt engine has the center 3 caps with 4 bolts each thus that much more holding the crank down in place.