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Archive for August 31st, 2009

Motorcycle And Atv Cylinder Rebuilding Options

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 werent 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 60s and they were replaced by aluminum block motors with castin 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 wasnt castin; it is installed in the block after casting. The cylinder bore of the aluminum block is machined to 35 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 reheating 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 doesnt 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 wont 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 electroplating. 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 there was ceramic composites and Boron. All of these perform in about the same way as far as wear and durability. Then there was Nikasil. Nikasil was a new plating formula of nickelsiliconcarbide. It was harder than the others that came before it. For years you couldnt get a cylinder replated 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 replated or some called it recoated. 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 its castin or not youre only real choice is replacing it with another sleeve or a sleeve liner.

Lets assume youre an avid racer and race 25 weekends a year youre 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 500600 for the top end and expect to do the same next year. 2 replate it for about 300400 with piston kit and gaskets and figure on doing it again next year. 3 have it sleeved for about 250350 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 presleeve bore finish accurate flange machining and sleeve made from the proper alloys. The most popular sleeve is the Moly 2000 chromemoly iron. The proper boring and honing to match the piston clearance requirements goes without saying.

Pros and Cons

RePlated Cylinder Bore
Pros
Small advantage in heat transfer
Slightly better wear factor
Somewhat lower coefficient of friction
Weighs a few ounces less
Cons
Costs slightly more
Cant be bored when damage occurs
More fragile
Can flake and peel

Iron Sleeved Cylinder Bore
Pros
Costs less
Boreable for future over sizes
Honeable to keep bore true and proper ring seal
Can be worked with common tools
Can be replaced when needed
Cons
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. Replated cylinders are as close to original as you can get. So if youre happy with your OEM plated cylinder you should have it replated. If not have it sleeved by a company that has the reputation experience and warrantees to protect your investment. http://kustomkraft.com

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