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Sleeves and Liners – Metallurgic Magic

Dry sleeves and wet liners have long been used to repair and restore cracked or worn engine cylinders, but they are also used to reinforce aluminum blocks that are being built for serious performance applications.

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Dry sleeves and wet liners have long been used to repair and restore cracked or worn engine cylinders, but they are also used to reinforce aluminum blocks that are being built for serious performance applications. In the sport compact market, it’s not uncommon to have small four cylinder engines with big turbos making 800 to 1,000 horsepower. Stock blocks were never designed to handle that kind of combustion pressure so the blocks are usually beefed up by boring out the cylinders and installing some type of sleeves or liners.

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Ductile iron sleeves are typically the material of choice for performance builds because it is much stronger and less brittle than cast iron. Ductile iron sleeves and liners come in different grades and with different heat treatments. There’s a lot of metallurgy that goes into making a top quality high strength ductile iron sleeve or liner. Ductile iron is a cast ferrous alloy, consisting mostly of iron but also 1.5 to 3.0 percent or more carbon (which forms graphite spheroids in the metal matrix for added wear resistance), 1.0 percent manganese, and 1.0 to 4.0 percent silicon for added hardness.

The tensile strength, yield strength and elongation properties of a ductile iron sleeve or liner are expressed in three sets of numbers. A sleeve with a rating of 100-70-03 would have a tensile strength of 100,000 PSI, a yield strength of 70,000 PSI and an elongation factor of 3 percent.

Sleeve and liner manufacturers use different grades of iron, heat treatments and casting techniques for different applications. A cast iron repair sleeve that is going into a stock Chevy 350 obviously doesn’t require the same strength and durability of a ductile iron sleeve that’s going into a Top Fuel motor. A536 is a commonly used grade of ductile iron, but depending on the heat treatment and alloys in A536 it’s tensile strength, yield strength, elongation and hardness can vary quite a bit. What’s more, some sleeve and liner manufacturers have developed their own proprietary ductile iron alloys that provide specific advantages over more commonly used alloys.

The tensile strength, yield strength and elongation properties of a ductile iron sleeve or liner are expressed in three sets of numbers. A sleeve with a rating of 100-70-03 would have a tensile strength of 100,000 PSI, a yield strength of 70,000 PSI and an elongation factor of 3 percent. Big numbers for tensile strength and yield strength are important for any engine that makes a lot of horsepower. The elongation factor reveals how much the sleeve can give before it cracks. A bigger number here is usually better too. Some ductile iron sleeves for racing have numbers like 135-70-06.

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By comparison, the average tensile strength of an ordinary gray cast iron engine block or gray cast iron repair sleeve is around 30,000 PSI. However, many centrifugally cast high-strength gray cast iron sleeves made of 691 material are about 1/3 stronger with a tensile strength rating of 45,000 to 50,000 PSI. How much strength you need for a particular engine will depend on the application.

The thickness of a sleeve also affects its strength. Most repair sleeves have a wall thickness of about 1/8-inch (0.125˝). A dry sleeve doesn’t have to be very thick because the bore surface in the block provides physical support around the outside of the sleeve. But in the case of a wet liner or an engine where the original bore is entirely machined away, the sleeve has to be much thicker because it has to provide its own support.

Centrifugally cast sleeves are typically stronger than poured castings, and sleeves with a flange at the top typically provide added strength and support in the critical upper cylinder area where combustion pressures are highest.

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The best advice for choosing sleeves is to work with your supplier so they can recommend a sleeve that will have the best physical properties for the engine you are building.

Custom sleeves are available from many suppliers, with prices ranging from $75 up to $200 or more for ductile iron sleeves.  Most have a spec sheet that you fill out with the necessary dimensions to order a set of custom sleeves.

One supplier told us that their custom sleeve business has really picked up recently. “We’re getting requests for all sorts of one-of-a-kind projects, everything from antique tractors and steam engines to hit-and-miss single cylinder stationary engines.”

Installation Challenges

Wet liners are usually fairly simple to install because little or no machine work is required unless an O-ring sealing surface inside the block is badly corroded or damaged. Although most wet liners in diesel engines are made of centrifugal cast ductile iron, there are some that use steel liners. Cat C18 and C32 engines have liners made from drawn seamless steel pipe. The outer dimensions of the liners are similar to those in the Cat 3400 and C15 engines, but they have a larger inside bore (5.71 inches/145 mm versus 5.4 inches/137 mm in the C15). The larger inside bore diameter reduces the wall thickness of the liner from 0.360 inches/9.1mm to 0.210 inches/33 mm. The thinner steel liners save weight but also provide 2 times the strength of cast iron liners and are less brittle and prone to cracking.

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Dry sleeves come in two basic styles: straight and flanged. Straight sleeves seat against the base of the cylinder bore and require a press fit to stay in place while flanged sleeves are locked in place by the flange at the top of the bore and require little or no press fit.

Locking compound is sometimes recommended with flanged sleeves to prevent oil from migrating up from the bottom of the bore behind the sleeve. This is more of a concern with aluminum blocks because of the difference in expansion rates between the aluminum block and iron sleeves. You don’t want oil creeping up behind the sleeve because over time it can form hard deposits that will distort the bore and cause ring sealing issues.

Installation recommendations vary as far as press fit is concerned. Generally, most suppliers recommend .001 to .002˝ of interference for dry straight sleeves that are being installed in a cast iron block. Some say you can use as much as .0025 to .004˝ of press fit in a cast iron block. On aluminum blocks, recommendations range from .0005 to .001˝ for straight sleeves to as much as .0025 to .003˝. With flanged sleeves, zero press fit to maybe .0005˝ is all that’s recommended.

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Some engine builders like a tighter press fit because it reduces the risk of a sleeve slipping. A tighter fit also helps improve metal-to-metal contact, heat transfer and cooling between the sleeve and block. But too much press fit in some blocks may also increase the risk of distorting the sleeve and/or cracking the block, especially in engines that have relatively thin castings in critical areas around the bores.

The relative smoothness of the cylinder after it has been bored combined with the finish on the outside diameter of the sleeve also affects interference fit and how easily the sleeve can be inserted into the block. Chilling the sleeves and/or heating the block (to 275 to 400 degrees in an oven) makes installation easier. But the time you have to complete the task is limited because the sleeves quickly heat up while the block is cooling down. Consequently, a sleeve may not be fully inserted in a cylinder before it starts to swell and bind up. For this reason, some say it is better to install the sleeves at room temperature. Plus you don’t have the risk of burning yourself on a hot block.

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One thing you never want to do when installing sleeves is to use a hammer and a piece of wood to beat the sleeve into the block. That may have been okay back in the 1950s, but on a performance engine with tight tolerances it’s asking for trouble.

The best installation technique recommended by several sleeve suppliers and boring equipment manufacturers is to make the bores as smooth as possible instead of just rough boring to size and pushing in the sleeve. A smoother bore means less friction during installation, and better metal-to-metal contact for improved heat transfer after the sleeve has been installed.

Whether you use a conventional boring bar or a CNC machine to bore the cylinders doesn’t matter as long as you use a feed and speed rate that leaves a relatively smooth hole. The smoothness of a bored finish will depend on the type of tooling used and the speed and feed rate of the boring head. For example, if you are using a CNC machine to bore a standard cast iron block, a speed of 1750 RPM combined with a feed rate of 6 to 10 inches would probably give you a good bore finish. On a harder high alloy cast iron block, you might have to slow things down to 300 to 350 RPM with a feed rate of 2 to 3 inches per minute to achieve the same results. It all depends on the application.

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One equipment supplier said using inserts that have a large radius will leave a smoother bore finish. They recommend using inserts with a .032˝ radius.

Whether you use a conventional boring bar or a CNC machine to bore the cylinders doesn’t matter as long as you use a feed and speed rate that leaves a relatively smooth hole.

Another way to get a nice smooth bore is to follow up your rough boring operation with a hone. One engine builder who builds trophy truck engines bores the cylinders to within .003˝of final size, then hones with #220 or #280 grit stones to final size. This leaves a nice smooth bore that accepts a sleeve easily. In some instances, he may even hone with #400 grit stones to leave an even smoother surface finish to better heat transfer between the sleeve and block. Of course, it’s also important to use sleeves that have a relatively smooth finish on the O.D. so they don’t gall or bind as they go in.

Using a torque plate to load the block when boring, and especially when honing, is also recommended to get round, straight holes. If there is any distortion in a bore before a sleeve goes in, it can distort the sleeve. And if the sleeve isn’t round, the piston rings won’t seal well against the sleeve and you’ll have a blowby problem.

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Nick Britton of Victory Machine in Winchester, VA says his use of torque plates depends on the engine he’s building. “On some of the engines we do, I won’t use a torque plate when boring the block because it saves time and doesn’t seem to make any difference as far as bore distortion is concerned. But I will install a torque plate if we are honing a cylinder after it has been bored. That does make a significant difference. And some four cylinder blocks we don’t hone at all because it can distort the block. On those engines, we are installing flanged sleeves.

Britton says he’s been boring blocks for 10 years and has never used a traditional boring bar, only CNC equipment. “CNC is so much faster and more accurate. It’s important to choose the right insert material, the right shape and lead angle to get a good high quality finish. Deburring after boring is also important. The tops of the bores should also have a small chamfer when you are installing sleeves to reduce the risk of galling. With flanged sleeves, a chamfer also helps prevent the O-ring from failing under pressure when the engine is running.”

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On some applications, CNC boring equipment must be used instead of a conventional boring bar. An example would be an engine that is being bored to accept flanged sleeves where the lips of the flanges overlap with one another. These have to be precision cut so they will fit correctly.

Finishing Up

Something else that’s important when installing sleeves is to make sure the bores are perfectly clean before the sleeves go in. You don’t want any metal chips or honing debris between the sleeve and cylinder bore. Britton says he wipes down the cylinder bores with acetone before he installs the sleeves.

Straight sleeves that are not precut to exact length have to be trimmed once they have been installed. Any metal that protrudes above the deck after the sleeve has been installed must be machined flush with the deck surface. A common mistake here is machining flush a sleeve that is not fully seated. If there is a gap between the bottom of the sleeve and the lip at the bottom of the bore, the sleeve may loosen up and slip out of place.

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With flanged sleeves, the depth of the counterbore at the top of the cylinder must match the thickness of the flange. If the top of the sleeve protrudes above the deck surface, the counterbore needs to be cut deeper, or the sleeve needs to be machined flush with the deck.

Most liners are prefinished so no honing is required once a liner has been dropped in place. Many sleeves are also prefinished, but if they are not they must be honed to a finish that will work properly with the rings. For most applications, a plateau finish is usually best because it provides rapid ring seating with minimal blowby.

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