The Cylinder Block — The Foundation

The engine block is the main structural piece of the entire engine. Everything else bolts onto it or fits inside it. Think of it as the skeleton that holds the engine together. It is a heavy casting — either cast iron or aluminum — with cylindrical holes bored through it. Those holes are the cylinders where the pistons move up and down.

Cylinders — the round holes where the pistons travel. The cylinder walls must be perfectly smooth and round because the piston rings seal against them. Any scratches, scoring, or out-of-round conditions in the cylinder wall allow compression and oil to leak past the rings. Coolant passages — channels cast into the block that allow coolant to circulate around the cylinders and absorb heat. Oil passages — drilled channels that deliver pressurized oil to the crankshaft bearings, camshaft bearings, and other moving parts. The main bearing saddles — precision-machined surfaces at the bottom of the block where the crankshaft sits and rotates.

Cast iron blocks are heavier but extremely strong and durable. They handle heat well and resist wear. Aluminum blocks are much lighter — saving fuel and improving performance — but aluminum is softer than iron and requires iron or steel cylinder liners pressed into the bores to provide a wear-resistant surface for the piston rings. Some modern aluminum blocks use a special plasma-sprayed coating on the cylinder walls instead of liners. The trade-off with aluminum is always weight savings versus durability and repairability.