AFAIK, the upper end is primarily the heads and associated parts above the main block.

The lower end is the main block, crankshaft, pistons, etc.

As Mike said in most situations the upper end is what needs rebuilding unless you think your main bearings (on your crankshaft) are going south on you. <img src="/forums/images/graemlins/kewl.gif" alt="" />

Off Roader
98 Montero with the Winter Package
89 Montero minty clean and reserved for overlanding trips or Cars and Coffee events
96SR (3.15:1 xcase, 35's) gone to the rust gods
96SR Build Up Thread
Old web page
Old web page