Click on a thumbnail to see the full-size image
Engine Blocks & Cylinder Sleeves
Thanks in part to natural attrition and the high price for scrap metal in the past few years, good cores for popular domestic engines have been getting harder to find.
By Doug Kaufman
Page 1 of 2
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.”
Page 1 of 2