Making the Top Engine Cap

The first thing is to highlight a group of polygons around the edge where the cap will go. Use the loop regulizer script to make the polygons into a circle then clean up the edges. Once finished cleaning up, extrude the circle part up a little bit as seen in image 1.

To make the cap, start with a new cylinder and start with 64 sides. Then add loop around the bottom so that the whole side doesn't indent (as seen in image 2) highlight 4 Polygons in a row every other 4 polygons and use the bevel tool and bevel inwards and then move those polygons so that the top edge is inline with the top edge of the cylinder then delete the top polygon and cap the boarder. After that, inset the top polygon and then bevel and then inset and bevel again to achieve the result as seen in image 2.