Performance Cylinder Sleeves
Many performance enhancements being "discovered" today are actually products or processes that were developed decades ago. One of those early developments that was not forgotten is cylinder liners.
By Doug Kaufman
In the performance segment of the automotive aftermarket, young enthusiasts often think only the latest is great enough for their vehicle. Thanks to the prevalence of computerized engine management systems, some might believe that high-tech guarantees high horsepower. Yesterday's technology? No way will it find success on the street or strip.
However, engine builders know that many performance enhancements being "discovered" today are actually products or processes that were developed decades ago.
In some cases, restoration engine builders have opened up an old engine from the 1920s and and found things they have previously believed to be invented decades later. Roller cams and variable cam timing are both examples developed early in automotive history.
Experts say that in many cases, early vehicle manufacturers had the luxury of trying innovative engine and component designs. However, because they didn't have the metallurgy or manufacturing precision to reproduce those parts for the mainstream, the easier, more conventional designs won out.
One of those early developments that was not forgotten is cylinder liners. Sleeving was developed back in the early 1900s when nearly all motors were built with replacement liners. Tractors were the primary motor vehicle in use then, said one sleeve manufacturer. Sleeving was a creative idea that allowed a mechanic or machinist to repair damage to one or two cylinders without having to replace the entire engine. Once it became a proven technology, it expanded to include virtually the entire industry.
But, as technology progressed, manufacturers realized it would be less costly to build blocks from a single mold rather than a block that had replacement sleeves. Big, heavy, solid cast iron blocks with lots of cylinder wall thickness became commonplace, and engine builders became adept at boring the cylinders to oversize and getting the engine back into service. But when the block would fail, hurting the block beyond the point of simply boring it oversize, the solution would be to continue to bore past the damaged area, allowing for the insertion of a repair sleeve.
In the standard rebuilding market sleeves continue to be as common a repair as any other process. When used to refurbish the bore and change the bore sizes, cylinder sleeving offers to the standard rebuilder market a reasonably inexpensive solution to replacing an engine block.
Some sleeve manufacturers say the lion's share of the engine resleeving market is in this "non-performance" segment. Perhaps 70 percent of the market is common cast iron for conventional repairs, low cost, easily attainable and relatively straightforward when it comes to installation, yesterday's technology still makes today's engines last.
But the performance segment also sees significant benefits from cylinder sleeving technology. As manufacturing technology has evolved, engines have gotten smaller and yet more powerful. And as is always the case, the demands for even more performance continue.
Unfortunately, not everyone understands the ramifications of that search for power. Simply adding aftermarket components won't necessarily do the trick - and may do more harm than good.
"Today a large number of 18- to 24-year-old kids have a budget just big enough to hotrod their Honda Civic or their old Subaru 2.0L They throw on a turbocharger and maybe a nitrous kit and suddenly the block goes 'boom,' and cracks or distorts the cylinder deck," explains one performance sleeve maker.
"At every level of racing, the percentage goes to the guy who makes more horsepower," explains the president of one sleeve manufacturer. "All racers desire to get as much out of the engine as they can within the legalities of the sanctioning body. With superchargers and turbos, for example, it all comes down to the integrity of the cylinder. The strength of the cylinder makes that possible."
In the performance and racing segments of the market, cylinder sleeving is intended primarily for durability, say manufacturers, to increase the quality of the base materials. And the increases can be extremely dramatic. One manufacturer, with a patented modular integrated deck sleeve design that assembles together like pieces of a puzzle, offers a sleeve kit that converts the engine from an open deck 100-hp automobile engine to one with a replaceable wet sleeve in an engine that will produce 1,200-1,500 hp. "That level of performance increase surprises even me," says this manufacturer's president. "You'd think at that kind of horsepower increases there would a weakness, but these Honda engines are amazing and no one seems to have found the weakest link yet. The performance sleeve gives cylinder integrity to have more compression, more rpm, more everything, so, in the parlance of the racer, they can lean on it a little more."
Materials and Design
Today's cylinder sleeves come in a wide variety of materials that are appropriate for different applications. They may be manufactured from cast iron or ductile iron, as well as aluminum; each type of metal may also have different levels or grades of quality within them.
Manufacturers are the experts when it comes to which type of material is appropriate for which application. Cast iron (or gray iron) is usually a very brittle material, but does a good job when it is contained within an engine. It has good wearability and heat transfer.
Ductile iron is not a single material, but a family of cast irons distinguished by its microstructural features. Engine Builder columnist Norm Brandes explains the difference this way:
"To the naked eye, both types appear to be extremely smooth. Under a microscope, however, there is a clear difference between gray iron and ductile iron. Gray iron has a more textured appearance, with a surface made of larger, coarser-shaped granules or graphite flakes. Ductile iron has a smoother appearance, made of smaller, more rounded graphite nodules."
These graphite nodules act as "crack-arresters" and give ductile iron ductility and toughness superior to other cast irons, and equal to many cast and forged steels. Manufacturers often produce sleeves in different grades, including some that have been engineered and chemically altered for additional strength.
Aluminum sleeves may also be used for certain applications, especially for use in aluminum blocks. However, aluminum cylinder liners require a bore coating such as a nickel silicone carbide coating. In most cases, these cylinder liners are reserved for the highest levels of racing.
Wet Vs. Dry
Because friction, compression and combustion all contribute to the generation of heat, a cylinder's walls must transfer excess heat to be efficient. Overheating will result in damage to the engine components. Heat transfer is a topic engine builders are familiar with, and it's one with particular ramifications to the cylinder sleeve.
Material differences notwithstanding, there are two 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.
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.
The wet-type sleeve is also press-fitted into the cylinder. The difference is that the water jacket is open in the block and is completed by the sleeve. Because it gets no central support from the block, it is made thicker than a dry sleeve. Also because the sleeve completes the water jacket, it must fit so it seals in the coolant. This is accomplished by using a metallic sealing ring at the top and a rubber sealing ring at the bottom.
Although they are pressed into place, installation of cylinder liners has become much more precise. "It used to be that you would put them in using a hammer and a crowbar," says one manufacturer. "That may have been okay with a flathead Ford, but today, even in cast iron blocks, we've migrated to more of a net fit. It's still an interference fit but it's a lot less friction than it used to be."
When a dry sleeve goes into a parent material that's a like metal - cast iron to cast iron, for example - the metallurgy allows heat to dissipate into the block. But an iron sleeve installed into an aluminum block comes with a bit of a handicap, says one manufacturer, because the dissimilar metals expand at different rates, impeding heat transfer somewhat. Because the aluminum grows away from the sleeve in use, the heat contained in the liner has to jump the resulting airspace. It can be less efficient when cooling and may be problematic over the long term.
Wet sleeving puts the cooling medium in direct contact with different parts of the sleeve and allows heat transfer to be more efficient, especially in bimetallic engines.
Proper sleeve installation takes as much precision as any other shop operation, and equipment suppliers have created machines that enable incredible accuracy.
Manufacturers say engine builders used to be able to put sleeves in in a casual way, but like most other aspects of this business, the casual approach just doesn't work any more. "Today, if an engine builder isn't CNC equipped, he's not competitive anyway - engine sleeving takes just as much precision as any other machining operation," explains one expert.
Norm Brandes, who has a well-deserved reputation for getting even more out of new performance engines while maintaining their emissions-legality, says the precise nature of newer engines means more precision is needed when measuring cylinder walls. As one honing expert told me, "When the clearances are specified down to .0005", you can't get away with measuring your work to within .001"."
Although a cylinder liner can correct flaws in an engine block - even catastrophic ones such as "windowing" in Top Fuel engines - rebuilders should never expect that their installation process can be loose. Knowing that the "sleeve will fill the space so it doesn't have to be precise" is a sure recipe for failure.
Brandes explains that in some cases, sleeves found in late model engines cannot be replaced. "Most sleeves are pressed or pinned into the cylinder, and a skilled rebuilder with the right equipment can replace these sleeves. But a 'cast-in-place' sleeve is impossible for anyone to replace."
A "cast-in-place" sleeve is inserted into the mold before the engine block is cast. As the molten metal is poured into the mold, it totally surrounds the cast-in-place sleeve. There are ridges on the outside (the side in contact with the block) of the sleeve. The molten metal fills these ridges, forming an interlocking bond between the block and the sleeve.
"By the time you bore out the parent material to make a smooth enough register to install a new sleeve, you have only paper-thin walls left," says a leading sleeve manufacturer "This makes installation of sleeves very difficult. Rebuilders are forced to go to no press at all and use adhesives to hold the liners in place. This might be okay for a street car but it presents a real problem for a performance engine."
This lack of cylinder stability or integrity in the block is what led to the development of the modular sleeve design. "By the time you bore out the block there was paper thin aluminum. You can't sleeve it properly and so there goes your good customer relations," says this company's president.
Sleeve manufacturers say the increase in cast-in-place liners is an attempt by vehicle manufacturers to sell new engine blocks rather than giving up the market to rebuilders. The OEMs don't want the blocks resleeved: they'd rather sell another block.
Despite the efforts of the OEM, however, performance sleeving is likely to continue for some time. New materials, new coatings and new installation methods will always be driven by the customers' desire to perform in a certain environment and at a certain cost.