Making Your Stock Block Better With Darton MID Sleeves

Traditionally when you think of sleeves, you think of clothing, or maybe even tattoos, but this is EngineLabs, and while we do our best to be up to date on clothing and body-modification fashions, when we talk about sleeves, we’re talking about the cylinder liners that are found in aluminum and some iron engine blocks. Since we usually like to go with the aftermarket side of engine technology, that means we’re probably talking about Darton Sleeves.

In particular, this video takes a look at Darton’s Modular Integrated Deck – or MID – sleeves, which are a unique design, patented by Darton, which consists of individual wet sleeves (which install directly into water jackets) with a flange. When siamesed with the other sleeves in series, the MID sleeve creates a new, stronger deck surface in addition to a new cylinder wall, for the ultimate design in high-power aftermarket sleeves.

Casting Aspersions

“The biggest issue with the OEM setups is that most of them, come with a cast iron sleeve in them,” says John Catapang, General Manager of Darton Sleeves. “[Cast iron] is a lower-grade material that is used for its cost-effectiveness with a tensile strength of maybe 30,000 or 40,000 psi.”

In addition to not being the strongest material option, OEM cast-iron cylinder liner thicknesses can often leave something to be desired in the realm of the performance aftermarket, especially when it comes to increasing displacement via overbore.

“They are cast thin because the OEM isn’t trying to go to a bigger bore. They are making their product to their design specifications, with no thought towards aftermarket alterations,” Catapang says.

The MID sleeve design turns an open or semi-open deck block into a closed deck design with the modular integrated deck (MID… get it?). The siamesed bores are able to be replaced individually in the event of damage.

To compound the issue, cast iron isn’t a particularly ductile material and doesn’t respond well to any kind of distortion forces. Any kind of movement or flex in that cylinder, and it will end up cracking,” says Catapang. “That is a problem if you are trying to add more power than what came from the factory, be it through higher boost, higher compression, or whatever.”

All of those issues are compounded by open-deck block designs, which don’t offer proper cylinder support under increased horsepower conditions. Without that structural support, you can get sleeve walk in a high-performance application,” says Catapang. “Once again, with any movement, you start cracking cast iron sleeves, as well as pushing out head gaskets. However, ultimately it’s the material that is your limiting factor. If it doesn’t crack it will distort and go out of round due to lack of support.”

The MID Fix

The first fix offered by the Darton MID sleeve is in the material used. “Our MID sleeves are made from a proprietary ductile iron material. It’s based on an ASTM spec for ductile iron, but we’ve tweaked the metallurgy to be able to work with a piston ring better than standard ductile iron,” says Catapang.

The advantage of the ductile iron isn’t limited to just the ability to withstand distortion and flex, but also much-increased tensile strength. “When you replace your cast iron sleeves with MID sleeves, you end up with 100,000-130,000 psi tensile strength sleeves, that are still ductile and will give instead of breaking.”

Additionally, because the MID sleeves are a wet sleeve design, they replace the thin OEM sleeve, and the block’s OEM cylinder completely, not only giving you a stronger cylinder completely, but adding thickness to put some extra bore in the stock block.

As the MID sleeves are a wet sleeve design, they install directly into the coolant passages. That means the OEM cylinder liner wall has to be removed along with the OEM sleeve (left). Once removed, the block is machined to accept the new MID sleeves, with their integrated deck.

“You’re looking at maybe .030-.040-inch of OEM sleeves, and another .100-inch in aluminum that we’re replacing with a full wet-sleeve design,” Catapang says. “What we’re doing with the MID sleeve is eliminating all that free-standing cylinder wall, which is technically the weakest part of the block anyway. By eliminating that portion of the block and installing our wet sleeve, that allows full support of the upper deck of the block, with zero movement.”

With the MID sleeves’ namesake, the integrated deck, you are also taking your open-deck or semi-open-deck block, and effectively turning it into a much more dimensionally-stable closed-deck Siamese-bore design, often found in aftermarket performance engine blocks.

However, these parts are far from drop-in replacements, and do require precision machining of the engine block for their installation. “We provide the installation manual with the step by step processes, and all of the machining tolerances and blueprints.” Catapang says. “If you adhere to the directions, specifications and tolerances, typically we’re talking .001-to-.0005-inch, you should never have a problem with [the sleeves] shifting.”

Down on the Deck

The Darton MID sleeves are much more than just sleeves, creating a closed deck block as was mentioned earlier. With a new deck in the block, there are a variety of machining options available for high-performance applications. Obviously, the end user could opt for a traditional flat deck, where the block and sleeves are perfectly flush with one another. However, another interesting option exists for the sleeve installation.

“A lot of times when you get into the higher horsepower applications, some people prefer to step deck the cylinders, where you’re leaving the compression area .002-.003-inch proud of the block surface,” Catapang says. Step-decking has similar benefits to running a compression O-ring, by increasing clamp-load around the cylinder, but a more traditional wire O-ring is also an option.

Once installed, there are two options for deck height. A flat deck is exactly as it sounds, with the sleeves being flush with the surrounding block surfaces. Then there is the stepped deck option, which, like an O-ringed block, provides additional clamp load on the combustion-sealing surfaces.

“If you are going to the max bore size, a lot of times there’s not room for a seal wire at that point. So you would go to a step deck to get a better crush on the head gasket,” Catapang says. “We’ve even seen some really high horsepower applications step deck in conjunction with a seal wire.”

Another awesome feature, from a high-performance application, is that if you damage a cylinder, or bank of cylinders, is that you can easily swap just the damaged cylinder out and salvage the rest of the sleeves and block.

“All of our wet sleeve designs can be replaced individually, or as a set,” says Catapang. “The technology is very similar to diesel tractor type engines. What we did, was take that concept, and engineer it for a new application. By putting the O-ring to seal the sleeve on the bottom, it makes the sleeve completely replaceable without bothering the cylinder next to it.”

While Darton’s MID sleeves might not be the right choice for every high-performance application, they are an awesome option to have available, especially when an aftermarket block isn’t an option for your build, for whatever reason.

A cool video of an inline-five-cylinder Volvo block being machined for Darton MID sleeves:

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About the author

Greg Acosta

Greg has spent over a decade in automotive publishing as Senior Editor of Race Pages magazine. In his free time, he is a firearms instructor and volunteer in the police armory.
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