Small Engine Maintenance
by THOMAS SCHUENEMAN
Small Engine Maintenance
Motorcycle-ATV-Snowmobile- Personal Watercraft-Outboard Cylinder Repair
Cylinder Sleeving VS. Cylinder Plating
Modern small displacement engines use a variety of cylinder types. There are iron type cylinders and plated type cylinders. Original equipment manufactures (OEM) produce many variations of both types and all are excellent performers and very reliable. The only real issue is how do I repair my cylinder after a failure? You may think you��ll never have to face that problem, but if you keep your vehicle or toy long enough you will eventually have to make this decision. In the following article I��ll try to make that decision more enlightened.
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.
Near the end of the last century it was discovered that you could make a mold pattern using a computer aided molding system out of Styrofoam. This made it possible to have precise duplicate patterns of a particular cylinder that you wanted to mold of aluminum. These are placed in a mold made of sand, molten aluminum is then poured slowly into the mold melting and replacing the Styrofoam pattern. This process is called total loss mold casting. Now all they have to do is a little milling and drilling, plate the bore and hone to size. For the two stroke market the best part of this is the finished product is an identical copy of the original. The factories love this because it just eliminated a whole lot of assembly line workers. No more absenteeism, no health insurance or pensions, and no coffee breaks. As far as the consumer goes they get a cylinder that doesn��t need a lot porting before they can be competitive.
There are a lot of four stroke motors that use aluminum blocks and aluminum sleeves that are plated a variety of hard finishes. These sleeves can be removed and replaced. The replacement sleeve can be either iron or aluminum. If you want an aluminum sleeve it will have to be plated after installing otherwise it won��t be true and round.
There are several types of plating that has been used over the years, and the companies doing plating guard their formulas carefully. The finish in the early years was a simple chrome or hard chrome electro-plating. The plating was generally only a few thousands of an inch thick. If it was more than about ten thousands of an inch thick it was prone to chipping or flaking because of heat expansion and contraction. In the early seventies Electrofusion became popular. Electrofusion was different from electroplating in as much as it was a fusion process instead of electroplating. Next came ceramic composites and Boron. All of these perform in about the same way as far as wear and durability. Then came Nikasil. Nikasil was a new plating formula of nickel-silicon-carbide. It was harder than the others that came before it. For years you couldn��t get a cylinder re-plated when you damaged one, the only way to get going again was to buy a new one. Now you can choose from many companies doing their own version of Nikasil.
