Recent History of Cylinder Types

The oldest and most common method of cylinder design is a cast iron block that is machined with a cylindrical bore directly from a solid casting. There is also a cast iron block that incorporates a sleeve that is pressed into the iron block. Generally iron block motors weren't very successful in small engines. Most small engines were used in vehicles and equipment that needed to be light and mobile. This made cast iron blocks undesirable for this purpose. There were a lot of single cylinder motors used in lawn mowers, construction equipment, scooters, small tractors and small motorcycles that used cast iron block motors in the early years. These began to disappear in the 60's and they were replaced by aluminum block motors with cast-in iron liners.

This opened the door for new lightweight motors that could be used in many more applications and in bigger displacements than ever before. This was accomplished by placing a cast iron sleeve into the mold before the molten aluminum was poured into the mold. This made the sleeve an integral part of the cylinder block. The sleeve usually had locking rings or flanges around the outside to prevent it from slipping in the casting as the engine expanded from the heat generated by the combustion process. A major problem occurred often when air pockets would develop during the casting operation around the sleeve. This caused hot spots and often caused premature engine cylinder failure.

There is another type of aluminum block with a cast iron sleeve that wasn't cast-in; it is installed in the block after casting. The cylinder bore of the aluminum block is machined to 3-5 thousands of an inch less than the sleeve diameter, block is then heated to around 600 degrees Fahrenheit, and the sleeve is dropped in. When the block cools the sleeve is held in place by the interference fit and the flange at the top or bottom of the cylinder. This cylinder can be rebuilt by simply re-heating the block to 600 degrees and removing the old sleeve and replacing it with a new one. Of course the finish bore will have to be machined to size and honed.

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