If you're confused about the difference between re-plating or installing a sleeve in your two stroke engine, this page will answer all of your questions. We offer both services at Ken OConnor Racing.
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.
Now lets look at a persons choice of repair or rebuilding methods for their Motorcycle, ATV, Snowmobile, Personal Watercraft, or Outboard. You can have your Nikasil or other plated cylinder re-plated (or some called it re-coated). This includes the composite types.
Or you can have it sleeved with a hardened alloy steel or cast iron (when you add alloys to iron its considered steel). If your cylinder has an iron sleeve already, whether it's cast-in or not, you're only real choice is replacing it with another sleeve or a sleeve liner.
Lets assume you're an avid racer and race 25 weekends a year, you're going to need a rebuild of your cylinder by the end of the year no matter what type cylinder you have. If it is a plated type cylinder you have three choices. 1- buy a new cylinder for $500-600 for the top end and expect to do the same next year. 2- re-plate it for about $300-400 with piston kit and gaskets and figure on doing it again next year. 3- have it sleeved for about $250-350 with piston kit and gaskets and next year have it bored (most models) to the next size for about $55 plus piston kit and gaskets.
A properly sleeved cylinder will perform as well as any plated cylinder. A properly sleeved cylinder is one that has the proper interference fit, proper pre-sleeve bore finish, accurate flange machining, and sleeve made from the proper alloys. The most popular sleeve is the Moly 2000 chrome-moly iron. The proper boring and honing to match the piston clearance requirements goes without saying.
Pros and Cons
Re-Plated Cylinder Bore
*Small advantage in heat transfer
*Slightly better wear factor
*Somewhat lower co-efficient of friction
*Weighs a few ounces less
*Costs slightly more
*Can't be bored when damage occurs
*Can flake and peel
Iron Sleeved Cylinder Bore
*Bore able for future over sizes
*Hone able to keep bore true and proper ring seal
*Can be worked with common tools
*Can be replaced when needed
*Slightly slower heat transfer
The Bottom Line
Both systems perform equally well when professionally done, so it really comes down to economics. You can expect a sleeved cylinder to give more life for the money. Re-plated cylinders are as close to original as you can get. So if your happy with your OEM plated cylinder you should have it re-plated. If not have it sleeved by a company that has the reputation, experience, and warranties to protect your investment.
Author Thomas Schueneman