68 JULY-SEPT 2014 engine professional

Before we could have sleeves, we needed adeveloped metallurgical industry to pro-vide us with the proper kind of iron to actas a wear surface inside the engine cylin-der.

As might be expected, the “Iron Age”was born thousands of years ago ashumans discovered the earth’s crust isabundant with iron ore and put it to useas iron utensils, weapons, shoes for clovenanimals and the like.

Casting and forging began in theSeventeen hundreds with iron use in farmimplements, water wheels and started tomature as metal smiths discovered the useof blast furnaces, smelting and how toprocess chemical additions to the iron toimprove its use and provide for moreapplications.

By the 1800s, casting was starting tomature when the creation of “pig iron”,the essential ingredient of iron, was per-fected in pure form without impurities.Even today “pure” pig iron is the founda-tion of good cast or ductile iron.

“As cast” cylinder sleeves still are madetoday for various applications but mostlyin our industry the sleeves are manufac-tured using a centrifugal process, some-times referred to as “spin casting”Centrifugal casting is a age old process

having begun in Europe during the 1800s.This type of casting is used in jewelry, andvarious types of steel and pipes.

Centrifugal casting for sleeves came ofage in the USA during the 1950s as moreengine rebuilding and restorationsdemanded cylinder liner material be asgood as the parent cast iron blocks of theday. In the 1960s, the OEM market beganthe introduction of aluminum engine

blocks which ultimately required the largescale investment in cylinder sleeve produc-tion to support the new higher quantity ofaluminum blocks.

Today we have many choices of sleevematerial from aluminum, steel, composite,metal matrix, cast iron and ductile iron. Inengines there also choices of bore materialsfrom coated aluminums to sprayed oniron.

Whatever the surface within the enginecylinder it MUST be a wear surface able towithstand high temperatures, long serviceduty and resistance to ingested debris orcontainments in the oil. The description ofthe most sever service is probable dieselengines for trucks and off road earth mov-ing equipment. Sleeves within these enginesare very high grade irons and inductionhardened to over 400Bhn.

Conventional engine sleeving beganwith the need to repair cast iron engineblocks with cracked cylinder wall(s). Theprocess was straight forward; a boring barwas mounted on the block, a larger holewas made, as long as the increased boredid not break into the water jacket, and asleeve with 1/8 ,3/16, or ¼ wall repairsleeve was forcibly inserted into the newlybored hole with a substantial interferencefit. The sleeved hole was then re-bored and

Cylinder SleevesBY DAVID CLINTON

A red hot cylinder sleeve being produced on its way out of molding die after metal

is formed into raw casting.

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honed back to piston size. This type ofengine repair has mostly disappeared asthe result of the OEMs total conversion toaluminum engines and the emergence ofthe aftermarket block manufacturing busi-ness. This transformation in the sleeve sup-ply market has caused all the sleeve manu-factures to refocus on core markets such asPerformance, after market supply to spe-cialty markets, racing, and engine specialtyshops.

In the “good old days” when wepounded sleeves into the blocks, little con-cern was given to “cylinder seal”. Duringthe 50s and 60s engines were equippedwith breather tubes to evacuate crank casepressure. The result was a constant blackoil film in the center of the roadways andcaused motorcyclists to avoid the center ofroads like the plague. Later on came PCVvalves causing the engines to ingest thecrankcase particulate and consume it inthe intake system. No one ever gavethought to the root cause of this phenome-non, lack of cylinder sealing. Back then

one quart of oil consumed per thousandmiles was considered okay.

Today cylinder seal is the KING of allengine building from the OEMs to NHRAdrag racing. Pan pressure is the telltale signof cylinder leakdown. 0 leakdown is hard-ly attainable but as little as ½ % is routinein some engine build disciplines. TheOEMs have gone to much tighter clear-ances, on bearings, piston to wall, and theindustry as a whole has been adoptingrazor thin piston ring cross sections toincrease sealing, reduce friction, and pro-vide for less rotating mass. Oil viscositieshave thinned to the point that the OEMsare now specifying 0 weight oil, whateverthat is.

So finally we get to SLEEVES… Arethey still needed and relevant in today’sengine world? Absolutely! The sleeve is thebasis of the marriage in the cylinderbetween the cylinder wall, the piston rings,the piston and the film of oil on the sur-face which is the glue of the sealingprocess.

The beginning of a sleeve’s life startswith the chemistry and the desired materi-al. Conventionally we will concentrate oncast iron or ductile iron and the variousgrades of each. All other types of sleevematerial i.e. steel, aluminum require spe-cial treatments, surface coatings or specialhardening to create a surface hardnessacceptable to act as a cylinder sleeve.

Presuming centrifugal casting theprocess begins with the foundry men pre-heating the furnace and ladles. Based onthe selection of the material type, pig ironis the first in the furnace and when itbecomes molten the remaining chemicalsare added in a manner and formula whichwill assure an outcome of chemical per-centages that when checked after the pour-ing and cooling will reflect what is neces-sary to assure a homogenous and stablemetal product. As a for instance, Cast Ironwill typically end up with Carbon @ 3 to3.5%, Mn @ .45 to .90, Si @ .12, P @ .12max. This would equal, approximatelyASTM-A48 Class 30 cast iron. This mate-

After the cylinder sleeve has been produced in the die, it is then machined to the proper outside diameter during the raw cast machining process. Some sleeves are machined for upper flange diameters, as well as upper bore and lower bore diameters.

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rial would spec out at 30.000psi Tensile,hardness @ 196-249 Bhn and generally begraphite in micro structure. This materialwill also be very brittle but provide a goodcylinder wall wear surface, easy tobore/hone and straight forward break in.

The SAE society through the ASTMguides generally will specify mechanicalproperties, chemical content and microstructure which determines tensile andyield properties of each material. So if youwere searching for class 60 cast iron theASTM standard would provide you a doc-ument to analyze all the data. In mostmaterial specifications, especially alu-minum, or steel, you can receive a printedcertification of the material specs, the lotnumber, foundry date etc. In the castingworld this documentation may provide thesame data but without certification. Thismakes the foundry process critical toassure a dense consistent micro structurewithout porosity, occlusions, or hardspots. This is the challenge for allfoundries because unlike steal the cast partdoes not necessarily reveal all these thingsuntil the end.

I liken casting with a furnace, ladle andtechnicians/chemists as like my Mom bak-ing an apple pie; the chemicals must beadded in a precise, orderly fashion at par-ticular times and properly mixed to attainthe material specs the foundry is lookingfor. The temperature of the pour must bemaintained precisely and the mixture mustcontinually be degaussed (mixed) to assurechemical balance.

Now in the case of ductile iron (nodu-lar iron) we add much more complexity ofthe mixing, pouring and add the terminoculation. Inoculation is the final addedat peak temperature with Magnesium.This single event converts the moltenmaterial to a “nodular” structure unlikecast iron which is a flake structure.

Ductile iron was born in the 1940swith a research project at InternationalNickel Co. by Keith Mills. Many firmswere searching for ways to replace steelwith a suitably strong product but whichwould be less expensive. Because cast ironis brittle, the search for a strong cast mate-rial with “ductility” began. During theearly 1940 time frame there was rationingand shortages of alloys thought to be usedin cast iron to improve the ductility factor.By war’s end, two crucial elements becameavailable, Cr (Chromium), and Ni (nickel)The development of ferrosilicon (MgFeSi)made the casting of ductile iron easier andmore predictable.

In 1949 the first ASTM spec for ductileiron was issued as ASTM A339-51T; thiswas later replaced with the spec we havetoday, ASTM A 536 which depicts the var-ious grades and mechanical properties ofductile iron.

What is Ductile Iron? Well basically itis a cast form of iron with steel like prop-erties. Ductility means there is a distortionfactor without breaking so the opposite ofbrittle. This is expressed in the mechanicalproperties as “elongation” and listed as a% of distortion before breakage. Thisvalue ranges from 2-8% typically. There isalso a substantial increase in hardnessfrom cast iron, all the way up to 330Bhnwithout heat treating.

Then we have the strength factorexpressed as Tensile/yield in PSI, usuallyranging from 60,000 to 100,000 pounds.

Ford was probably the first OEM touse as cast stack molding of ductile ironfor rocker arms in 1949 and in 1951 con-

verted to 100% crankshaft production ofductile iron.

One of the uniqueness of the ASTMductile iron spec is that unlike other mate-rials, no chemistry is called out. This basi-cally gives free rein to the foundries toinvent their own recipes. Our firm DartonSleeves has researched the chemistry foryears and this was driven by an inquiryfrom Orenda Aerospace in Canada, whowas searching for an economical ductilesleeve for a V8 engine project destined tobecome a certified aircraft engine. Dartonwas selected as the vendor and the require-ment was for a sleeve to withstand 1500hours of use @ 75% horsepower and notwear out! This engine was certified by theCanadian DOT and the FAA in 2001.

This process was a long ordeal with alot of challenges but we finally succeededand we supplied the first 100 parts whichwere destined for robotically controlledengines in test cells which ran 24 hours a

CYLINDER SLEEVESBY DAVID CLINTON

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day for weeks. At the conclusion of the tests all enginecomponents were evaluated for wear; the sleeves onlywore only .002!! Now I know what you’re thinking, myChevy ran 150,000 miles and was still going strong!The difference is average driving is accomplished atabout 20-25% peak power output so your Chevy wasbasically loafing for 150,000 miles.

All of this was made possible by chemistry andfoundry procedures. Today this chemistry is the basis ofour top grade of ductile iron (DDI-2007A) we supply toall of our Top Fuel and Funny Car customers. Thismaterial is 140,000psi tensile strength, 80,000psi yield,4-5% elongation and 300Bhn hardness. Also this mate-rial is the densest commercial material available at 500nodules per square mm. Average ductile usually is in therange of 200 nodules per square mm. (More of this datais available at www.dartonsleeves.com.)

Darton is a pioneer in the sleeve business havinginvented in 2004 and commercializing a radical conceptfor sleeving engines called MID for “modular integrateddeck”. The concept was born out of the engine builder’sdesire using OEM engines to increase bore size and stillstay within the confines of bore spacing, two diametri-cally opposed concepts. Sooner or later increasing boresize usually yields weak block structure with thin wallsleeves, sometimes at .060 wall thickness. This justwon’t work; to contain combustion the cylinder needsstructure and wall (read mass). Remember sleeves willnot make up for missing mass, and cylinder distortionand leak down will surely follow.

The MID product effectively re-engineered the blockby providing integral and Siamese structure to eliminatebore distortion and provided for a solution by engineer-ing the product as a wet sleeve so they are easilyreplaced in the field. Just recently Dart Machinery intro-duced the MID product as an option in their new LSNext aluminum block and the Aluminum SBC. Dartoncurrently has about 50 different applications for theMID. Visit our web site for all the details.

Sleeves are not just “pieces of pipe”; ask anyfoundry or casting facility about the challenges in theprocess and they will usually tell you about the “oneguy” who makes all the recipes and consistency cometrue, the process is truly artful. Rodney Dangerfield saidit best; all he wanted was a little respect, just like ussleeve guys.�

engine professional WWW.AERA.ORG/EP 71

David Clinton is the president/CEO and founder of Darton Sleeves in Carlsbad, CA. For more information, call 760-603-9895 or visit www.dartonsleeves.com.

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