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Hi,
Cylinder Sleeves (or Liners) are nothing new. They've been around for 60 or more years. Using Cylinder Liners made Block Casting much easier and cheaper because Water Passages didn't need to be cast into the Block, the Coolant could just flow around the Liners instead, which actually provides better cooling.
Every Aluminum Alloy Block, had cylinder sleeves as the Alloy simply won't give long wear, it is too soft. Also, all Sleeves are merely slipped into the Block. My Esprit's Liners just slip in and have a bead of Hylomar (sealant) on the bottom to seal them against the coolant which flows around them (known as Wet Liners). This isn't a problem, because they mate with a lip machined on the bottom of the Block and are held in place by the HeadGasket and Head on Top, there's nowhere for them to go.
Traditionally, Steel or Cast Iron Sleeves were used. They provided good wear characteristics, had the same expansion rate as the Pistons and Rings. Also, Metallurgy was not so advanced as to offer any alternatives.
Fast Forward to the '80's and advances in Materials Science began to offer alternatives. Basically, coating an Alloy Sleeve with a Ceramic offered the same benefits as Steel ones, minus the weight, and it expanded at the same rate as the Block, allowing the use of Alloy Pistons, reducing the reciprocating Mass.
The first ones involved a Nickel/Silicon ceramic, commonly known by it's Trade Name - Nikosil. Many Motorcycle Engine Manufacturers started using them as well as Marine Engines and Snomobiles. Lotus was one of the first Car Manufacturers to employ them beginning with the 1986 Esprit. They offered good performance, but were very expensive as the R&D hadn't been recovered and no Economy of Scale was reached (the Liners in the Esprit cost $1200 each!).
The science continued to advance and Audi developed a process where Silicon was used exclusively. It was not coated, but actually cast along with the Block using a mixture of 25% Silicon and 75% Air. The Air was lost in the casting process leaving a coating of Silicon. It's Trade Name is Locasil (which is a derivitive of the phrase Lost Cast Silicon a reference to the Lost Casting process used since at least medival times). Porsche adopted this Liner technology for use in the M96 Engine. It actually impregnates the Bore in the Block with the harder silicon, eliminating the need for a sleeve or Liner.
There were some problems with the initial technology (the Silicon impregnation was not always uniform) and cars through the '98 Model Year were affected. Also, in the late '98 Model Run into early '99, Porsche's Engine Assembler received a shipment of faulty Blocks. Rather than slow Production (already behind Demand), the decision was made to use these Blocks with Locasil sleeved Liners and address those which failed later on a Case-by-Case Basis.
Since then, there has been no significant failure of this technology. Sure, some may occaisionally slip through the Quality Control, just as a Bad Piston could, but it is not an inherent issue.
As with all things Mechanical, these can/do wear out at some point and will need to be replaced, but probably well on the far side of 200k mi. with proper care (read not constant RedLine) and maintenance.
I'm afraid that your Service Tech is a little behind-the-times, because this just is not a significant issue anymore. He says that eventually every Engine will succumb to this, well the same can be said with respect to the Pistons, Crank, Cams, Valves, etc., eventually EVERY Engine simply wears out. Hope this helps...
Happy Motoring!... Jim'99
Last edited by MNBoxster; 09-08-2006 at 10:24 AM.
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