In our February 2009 issue, Technical Editor Larry Carley provided a comprehensive overview of the changes in engine blocks over the years. Thanks in part to natural attrition (after all, many of the most popular engines were actually designed and built more than 50 years ago) and the high price for scrap metal in the past few years, good cores for popular domestic engines have been getting harder to find.
Aftermarket engine blocks in cast iron or cast or billet aluminum are making it easier for engine builders to serve their customers. With the introduction of many affordable cast iron and aluminum castings for popular applications, engine builders now have more options than ever before. If you can’t find a good stock core to work with, you can start from scratch with a brand new aftermarket block.
If you want to minimize weight, aftermarket blocks offer considerable weight savings if you opt for aluminum over cast iron. Aluminum may cost more, but it can reduce the weight of the block to less than 150 lbs., depending on the engine. Most aluminum blocks use dry pressed in steel sleeves and billet steel main caps. Various deck heights and bore sizes are available to meet most needs.
Strength is critical in any performance engine, so some suppliers of aftermarket engine blocks are now offering compacted graphite iron (CGI) as an optional upgrade for certain engines. A block made of CGI, rather than ordinary cast iron is a good choice for a supercharged or turbocharged engine that is running a lot of boost pressure, or an engine that is being juiced with high doses of nitrous oxide (N2O).
CGI roughly doubles the strength of the casting but adds no additional weight. However, it’s not cheap. A CGI block will cost you about 40 percent more than an ordinary cast iron block.
Another option engine builders have today is to choose a billet block. In recent years, computer numeric controlled (CNC) machining has made possible a lot of things that were either too expensive or too expensive to accomplish by other means.
Computer-aided design and mapping now make it possible to copy or design from scratch an engine block on a computer screen and then machine it from a solid chunk of billet aluminum.
Billet blocks have a number of advantages over cast aluminum blocks, such as strength. Billet blocks are much stronger than cast blocks, with the tensile strength of a billet block being about a third higher than that of a 356 aluminum block. This improves rigidity, reduces block distortion and improves cylinder sealing under load.
Another advantage of billet blocks is weight. The thickness of a billet block can be machined down in areas where strength isn’t as critical. This can shave 20 to 30 pounds from the weight of a billet aluminum block, compared to a cast aluminum block. Billet blocks can also be repaired more easily than castings, by TIG welding. Finally, billet blocks can be easily customized to almost any dimensions (deck height, bore spacing, cam location, etc.).
But what about the times when you have a block that is in good shape with the exception of two or three cylinders? Whether you just need to refurbish a few of the engine bores, change the bore sizes in a standard engine rebuild or possibly add a little durability to a performance engine to carry a little more compression ratio, more rpm and more power, cylinder sleeving is a popular, proven technique.
A Sleeve is a Sleeve, Right?
Don’t be fooled by appearances, say experts. All sleeves are not created equal, even if they do start out with the same aspirations.
“The true definition of a sleeve’s purpose is to provide a wear surface for the piston rings,” explains John Catapang from Darton Sleeves. “Basically, sleeves are designed to ‘resize the bore’ to some known dimension, with the quality of the bore being returned to factory specs.”
Consequently, Catapang says, sleeves are generally supposed to be made of a material which provides an accommodating wear surface that also sacrifices a certain amount of material to facilitate the break-in process.
But, “just as with machine shops and technicians, all liners or sleeves are not the same,” says Steve Scott, IPD Parts, LLC. “The sleeve material, specifications, heat treating and the manufacturing process are all critical in producing a quality liner. You can’t skip one and expect an engine to perform correctly.”
Today’s cylinder sleeves come in a variety of materials that are appropriate for different gasoline or diesel applications.
“There are two types of sleeves,” says LA Sleeve’s Dave Metchkoff. “Centrifugal spun-cast iron and poured cast iron. Of those two manufacturing processes there are also two unequal material composites. There is the most commonly used iron which is simply called grey cast iron. Then there is ductile (also called nodular) iron.”
Poured cast iron is, not surprisingly, poured into a cylinder casting mold. Generally more prone to porosity and weakness, the grey iron material is only as good as its pour and heat treat. Air pockets or carbon deposits can be trapped within the walls of the castings. “If such sleeves are used in a high performance application, they can washboard the surface, crack or become deformed under heavy load,” says Metchkoff.
“The spinning method used to produce centrifugal spun-cast iron will draw the impurities and porosity and air pockets out from the raw casting material’s center to the outer surface, which will be removed while producing sleeves,” Metchkoff continues. “This creates a sleeve material with greater density and micro-structure, which will enable the sleeve to withstand greater loads without losing shape or cylindrical roundness.”
Grey iron is best used in an environment which is highly controlled, Metchkoff says. The installer or engine builder will be satisfied using the grey cast iron in an iron block with very stable wall thickness. The wall thickness is key because it will hold the sleeve in a stable area, ensuring good ring seal.
Ductile iron is twice as hard and strong as the grey iron and is appropriate for applications that are far less predictable, such as in very thin-wall iron block motors or most aftermarket aluminum blocks. “In aluminum blocks, where wall thickness is a major consideration, an engine builder will want to use ductile iron because the ductile material will actually reinforce the lightweight alloy blocks,” Metchkoff says. “The ductile can be warped under a heavy load, but it will return back to its beginning origin because it has tremendous memory. The material has the ability to adapt to the movement of the piston or aluminum block and bring it back to round.”
Installation and Interference
Material differences aside, there are two basic types of cylinder sleeves: the dry-type and the wet-type. Simply put, a dry-type sleeve does not contact the coolant, while the wet-type sleeve IS in direct contact with the coolant.
“A wet sleeve, when installed, completes the cooling system,” says Jay Wagner of MAHLE Clevite. “Without the liners in place there is no cooling jacket. The top is sealed by an interference fit somewhere in the counterbore area and this seal area can include sealing shims or seals. The bottom is normally sealed with O-rings in grooves, which can be either on the sleeve or in the block.”
The dry-type sleeve is pressed into a full cylinder that completely covers the water jacket. Because the sleeve has the block to support it, it can be very thin.
“These are our most common type of sleeve,” explains Mike Walsh of Melling. “Dry liners are not open to the cooling passage of the engine so no sealing ring is required. The dry type sleeves can be used as a new wear surface or as a repair medium for small cracks and holes in the engine block. Dry sleeves require a press fit and machining on the inside after installation.”
Flanged-top sleeves are commonly used in aluminum blocks, according to LA Sleeve’s Metchkoff and others because their design ensures that the deck surface remains stable. And it is this combination of form and function that allow all of the different styles to work within each recommended application.
“To promote proper cylinder seal with minimal ‘leak down,’ the cylinder sleeve, the pistons and rings and the assembly process must use the best assembly techniques and tooling and ensure a PERFECT marriage of the parts in a running condition, cold or hot,” explains Darton’s Catapang. “In other words, the cylinder bore must maintain perfect roundness and the rings must seat so as to prevent cylinder leakage. The sleeve and the way it is installed are the beginning of the process. Incorrect sleeve installation will surely promote cylinder distortion and subsequent leak down leading to poor performance.”
MAHLE Clevite’s Wagner agrees that it all starts with the engine block and counterbores for wet and dry sleeves must be flat, clean and parallel with the surface of the block.
“Each manufacturer provides the specs for allowable deviation. Proper protrusion must be maintained and there are limits to how much the protrusion can vary between the adjacent sleeves and overall,” Wagner says. “Most manufacturers provide shim kits to allow for the truing of counterbores and liner protrusion. Lower bore receivers on wet sleeve blocks must be square and undamaged. Damaged lower bores must first be repaired.”
Wagner acknowledges the ease that’s offered by specialized CNC machines but says an engine builder shouldn’t shy away from sleeve installation just because he doesn’t have the absolute latest equipment. “As far as special equipment is concerned, a good machinist can perform miracles with the simplest tools. Certainly, there is machinery out there that will make you more efficient, but if you don’t follow good machining practices when using it, the best machine in the world can still give poor results.”
Getting the sleeves into the cylinder bores and keeping them there are critical parts of the sleeving process. The term “press fit” implies a simple process of just pushing the sleeves in place, closing the hood and driving away. Walsh from Melling indicates, however, that in actuality, it’s a much more complex process.
“A sleeve needs to be measured carefully to determine the amount of press fit,” says Walsh, “and it should actually include an average of six separate measurements.”
Walsh says knowing the following measurements will help greatly:
1) Measure the OD at the top of the sleeve, in the middle of the sleeve and at the bottom of the sleeve.
2) Turn the sleeve 90 degrees and take the same measurements again.
“The average of these measurements determines the actual OD of the sleeve,” Walsh explains. “Some minor sleeve distortion may have occurred during shipping, but the sleeves will still conform to the shape of the cylinder.”
While other industry spokesmen say a standard number is .001? of press for every inch of sleeve diameter, Walsh cautions that these figures are for “perfect” to “normal” conditions and not for use in all applications. “The machinist’s past experience should also be considered, as well as numerous other factors that will affect the amount of press needed.”
Incorrect press will result in improper sealing and it’s more than just an annoyance. “If a wet sleeve is loose, besides the problem of leaking you can experience increased cavitation,” warns Wagner. “For many years we thought cavitation was the result of corrosion. While that’s still a slight possibility, the more likely culprit is rapid vibration and vapor bubbles collapsing on the side of the liner. These tiny explosions can eat away at the liner and eventually go all the way through.”
Just as bad as too loose, however, too tight a press can be a problem. “When sleeving an iron block it’s critical not to press the sleeves into the block to tightly,” cautions Metchkoff. The tight press fit can fracture or crack the original iron block. The straight wall sleeves commonly used in iron blocks may have a usual press fit of .002?, but if you’re sleeving all eight cylinders, you’ll need to consider that the block will stress somewhere. Therefore, we recommend much less press fit because as each cylinder is being sleeved, it will push material to the neighboring cylinder bore.”
In this case, flange-top sleeves require just .0001? to .0003? of press. The flange prevents the sleeve from dropping, and can be an excellent option for sleeving race blocks, Metchkoff says.
In any case, Scott from IPD reminds engine builders to follow the manufacturer’s guidelines and instructions. “While a cylinder liner or sleeve is designed to withstand the forces of engine operation within the cylinder block, they are somewhat fragile on their own and need to be handled accordingly. Heat-treated liners are susceptible to cracking if handled or installed incorrectly.
“The Ra finish of the liner bore, degree of angle of the crosshatch and roundness and diameter of the liner affect the ability of the rings to seal to the liner and play a major role in oil consumption,” Scott continues. “Induction heat treating and material hardness are factors in the service life and durability of the cylinder.”
Again, points out Scott, it comes down to how well the components work together. “Quality and fitment are two major traits to consider when selecting a liner. Considering that the cylinder components must contain and withstand the forces of the cylinders’ combustion, these are not parts that you want to skimp on. If the sleeve is perfect but the other engine components are not within specifications, the sleeves can be subjected to conditions beyond what they were expected to operate in.”
“Most heavy duty diesels have gone the way of the wet sleeve,” says MAHLE Clevite’s Wagner. “Cooling has become a very big concern, particularly with the implementation of EGR, and engine manufacturers are constantly trying to reduce the heat in the cylinder to reduce the amount of NOX that is produced.”
Melling’s Walsh says the same rules apply, whether you’re working with a gas or diesel engine: “Interference fit should be based on the extent of the damage to the block, the type of sleeve and the past experience of the installer.”
LA Sleeve’s Metchkoff echoes this. “As far as interference fit goes, the theories have actually changed a bit over the past few years. Therefore, if the sleeve diameter is 4.500?, the installer would consider .004? interference fit. In an iron block, that can be catastrophic. If the block has been mildly fractured, the press fit will possibly crack the block, rendering it disabled. But with the use of today’s high-tech sleeve retaining compound (available from Loctite), press fit is reduced greatly. Generally, the most press a sleeve will need in an iron block would be .002? and in an aluminum block it’s recommended to go with .0035.?”
Catapang from Darton says today’s sleeves offer a variety of materials and technologies to bridge the cylinder hole and the surrounding mass of the engine block. “By design and necessity, diesel sleeves are wet, thick walled and of superior material to withstand hundreds of thousands of miles of very high cylinder pressures and high heat. Conversely, small displacement car engines usually have aluminum engines with a ‘cast-in’ cast iron sleeve and minimal wall thickness separating the cylinders because of the low horsepower output.”
Still, despite the differences, the similarities are even greater. “The main and ONLY consideration to engine performance is to engineer a solution in which the expected horsepower output over the expected run duration of the engine is built to the task,” Catapang says. “Top Fuel engines are only supposed to last/perform for seconds. Indycar engines need to last 500 miles. NASCAR engines need to run or several hours over the course of a weekend, and street car engines need to last for thousands and thousands of miles.”
Though all involve different levels of performance, Catapang points out that the common thread is control of the combustion process. “In Top Fuel, for example, cylinder pressure may approach 25,000 psi and yet the sleeve is supposed to live and last multiple runs while sealing this tremendous pressure.”
Thanks to today’s technology, sleeve manufacturers are up to the task of supporting the performance enthusiast and engine builder alike.