Bottom Half of Motor

[Hammerhead]

I don't like the demarcation of "Top Half" and "Bottom Half" of a motor.
IMHO, a motor is best divided into thirds.
Top Third:
Everything from the head gasket up. If your head or cams are worn and this is what you replace, then you are not disrupting the bottom two thirds.
Middle Third:
Liners, pistons, block, connecting rod from the crank bearing up. This section of the motor cannot be accessed without undoing the other two thirds, but the other two thirds can be done without touching this or each other section.
Bottom Third:
Rotating assembly down. Rod bearings, main bearings, crankshaft, oil pump, etc. This section can also be serviced without disturbing the other two sections.

When you divide a motor in half, you can't service the liners, pistons, and such without removing the top half. The traditional phrase of "doing the bottom end" usually means rod & main bearings, and occasionally the oil pump. Doing only this is fine if you have inspected the liners with a boroscope. But if your planning to do this, and the top third, then it's just best to do a complete inframe at one time. There's no sense in doing bottom end bearings, then a short time later planning to do the top, you're buying the same parts and labor twice doing it that way.