Iron sleeves give a wear-resistant surface for the piston rings, and they don’t have to be very thick because they are supported by the surrounding block.
Cast iron blocks, by comparison, don’t need cylinder sleeves because the iron is very hard to resist ring wear. If a cylinder is broken, damaged or worn to the point where it can’t be reconditioned by boring or honing to oversize (because the casting is too thin), installing a press-fit dry sleeve can often save the block.
When a dry sleeve is installed in an iron block, a definite amount of interference fit is usually required to retain the sleeve and prevent it from slipping. Iron sleeves have the same coefficient of growth as the block, so typically require only about .0015% to .002% of involvement to lock a sleeve in place. Aluminum has a much higher coefficient of thermal expansion than iron, so the block tends to pull away from the sleeve when it gets hot. Consequently, more interference fit is usually required when an iron dry sleeve is installed in an aluminum block, say .003% to .004%.
Mike Walsh of Melling says his company now makes flanged dry sleeves for GM’s new Ecotec engines. These are a drop-in replacement that no need of interference fit. Melling creates sleeves for a wide range of automotive, truck and small engine applications using a centrifugal casting process, which Walsh says results in higher strength and tolerances that are exact to within one half of one-thousandth of an inch. Other new applications contain dry sleeves for GM LS1/LS6 (1997-2004), Ford 2.0L (1997 & up), and Lexus 4.3L 3UZFE engines in 2005-2006 models. New heavy-duty sleeve applications contain CAT 3116 and CAT C-7 3126 engines.
Round And Straight
Whether a cylinder sleeves is being installed in an aluminum or iron block, dimensional accuracy is an absolute must. The cylinders in the block should be machined as round and straight for a good fit. Concentricity of the bores is very important to minimize bore bend. Likewise, the sleeves must be manufactured to testing tolerances if they are going to fit properly. If the block or sleeves have too many different types, it can distort the cylinder bore and adversely affect ring seating and sealing, compression, blowby, oil consumption, and emissions. Severe bore bend may even cause piston scuffing if the clearance between the piston and wall is insufficient.
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