As the name implies, sleeves which are surrounded by water when installed are considered wet sleeves. The significant difference in sleeve design beyond the terms wet or dry are what structure within the cylinder carries the load. In a dry application they cylinder compressive force is carried by the sleeve and the block. In a wet sleeve application the compressive force is totally supported by the sleeve. Therefore, by nature of application and intended use, wet sleeves must be very strong and mechanically able to withstand compressive and frictional forces throughout their total unsupported length.
Cast iron and alloy sleeves and aluminum generally do not have the required structural strength and mechanical properties required for wet sleeve installations. This application normally requires high strength ductile iron or steel or hybrids of either. The features of the material to be used in a wet sleeve design are tensile strength, hardness and elongation. Although Darton lists ASTM 536-84 as our base line ductile iron, our material exceeds all the mechanical specifications by a wide margin. Darton currently produces variations of ductile iron but our base line performance material equals 130,000 psi tensile, 280-290 Bhn hardness and 5-6% elongation.
For wet sleeves, tensile strength determines the matrix strength of the part, hardness determines surface abrasion resistance and elongation equals flexibility with out memory to absorb shocks of combustion and resist permanent deformation. As compressive and combustive pressures rise, wet sleeves face enormous stresses caused by pressure, heat and ring friction. Without superior metallurgy these kind of sleeves would not endure. Typical diesel sleeve applications may reach 20-1 compression and turbo boosts of 60 pounds. In addition to mechanical strength, wet sleeves must be constructed of enough wall thickness to replace block integrity. No matter how strong the material is, mass and structure will determine performance and longevity. As a guideline, Darton does not recommend wet sleeve wall thickness under .150.
Dry sleeves are named so because the sleeve body is not exposed to any cooling liquid within the block and is always installed in a block with an interference fit. The usual interference value depends on the application and method of install. Darton recommends .001 – .002 interference on like material, i.e. iron sleeves in an iron block. When dissimilar materials are involved such as iron sleeves in aluminum blocks, and interference of as much as .003 can be used however, differential temperatures must be used for installation and the block must be perfectly prepared both dimensionally and surface finish. As a rule of thumb see the following table, which can be used as a guide for temperature differential for each instance and fit.
Technical Issues Concerning Sleeve Use and Installation
Sleeves may be manufactured from cast iron, alloyed iron, ductile iron, steel or aluminum. Within the iron category sleeves may be manufactured using an as-cast procedure or a more common “spin casting” process which in engineering terms is by a “centrifugal” die machine. Sleeve quality and consistency are more predictable using the centrifugal process. Darton produces all our sleeves except steel and aluminum using the centrifugal process and additionally Darton uses proprietary machinery to change rotational speed of the casting dies to manage the material compacting and density of certain chemicals within the material matrix. Please refer to material specifications under “Our Services” for specific chemistry and mechanical properties.
Steel sleeves are not normally used except in hybrid installations or where the necessary exits for ultra thin walls in the dimensions of .040 – .060. Although steel tensile strength is generally higher in the ASTM 4-5000 series steels, the mechanical properties of steel are not as well suited to cylinder liner usage without additional processing of the material such as heat treating and/or surface coating. When steel sleeves are treated and coated with hard-chrome or nicasil the sleeve becomes very strong and useful, however, the costs are very high, sometimes as much as 4-5 times more expensive than ductile iron. Cast, alloyed, ductile or steel sleeves are all acceptable for use in iron or aluminum blocks although different installation procedures are required in each circumstance.
Aluminum sleeves are considered specialty items and can only be practically used in aluminum block, dry sleeve applications. The main advantage of aluminum sleeves is weight saving and generally equal rates of expansion. Although aluminum may reach tensile strengths over 50,000 psi, the elongation in aluminum is not suitable for a wet sleeve application. In addition, aluminum sleeves will require bore coatings such as nicasil to perform as a cylinder liner. There are some materials of aluminum structure referred to as “MMC” or metal matrix which incorporate amounts of silicon and carbide to improve or permit piston ring abrasion resistance however, machining of this type of material is difficult and expensive.
Boring, Honing, Breaking in
Machining any material is essentially a “gouging” operation. There are many forms of this gouging we call machining but in all cases it can best be defined as “tearing away” material from a parent surface. The speed, process and finesse of material removal is graded by amount of material removed per revolution, the speed of removal and the final finish.
For boring to be predictable and the outcome stable, the speed, depth of cut, tool bit design and geometry, plus machine rigidity must be tailored to the job. In all cases of boring or honing sleeves in a block, a deck plate must be mounted and torqued replicating exactly the engine cylinder head. In addition, Darton recommends when boring ductile iron that the tool inserts be carbide and flush coolant be used. Darton recomends Rottler machinery be used for boring and block preparation. www.rottlermfg.com
When honing a deck plate must be used and the stones, pressure, and stroke should be directed by the honing machine manufacturer. Honing may become a two or three step process involving roughing, finishing and plateauing. In all cases of honing long dwells per hole and/or large quantities of material removal will generate heat, lots of it. This heat is usually absorbed by the sleeves and the honing oil. The concentration of heat, stone debris and metal will impact the surface finish, size control and sleeve distortion. Darton recommends Sunnen Company as the best source for honing equipment, procedures and technical assistance. Visit: www.sunnen.com
After sleeve wall preparation, break in is determined by application, piston-to-wall fit, piston ring fit and piston ring geometry. No matter which collection of parts are used, final break in does not occur until the rings have assumed a “barrel” face and the final oil is selected. High lubricity inhibiting “sheer friction” on piston ring face will prevent proper break in. Oils such as synthetics or ultra compounded oils are poor choices for break in and promote cylinder wall glazing. When a cylinder wall is glazed it will never satisfactorily break in. The break in is a finely harmonized event between cylinder walls, piston ring face and oil acting as a sealant aided by compression.
Other things affecting break in are excess heat, poor ring or piston fit, cylinder taper, assembly contamination and the list goes on.
Engine Break-in, Tuning
Fill the engine with a good grade of mineral oil (not synthetic) with viscosity for your bearing clearance and intended use. Prime the oil system before engine start with ignition off using the engine or dyno starter. We require break-in and tuning using an engine dyno or chassis dyno as follows:
- After initial start up, warm up engine at 2000-2500. Precaution should be exercised to prevent excessively rich or lean conditions, which will gall the cylinders. Monitor oil pressure and temperatures.
- After initial run, adjust valves if using adjustable valve train and retorque heads. Check for leaks.
- Street engines will require multiple run ins with increasing rpm and load up to maximum output.
Use of a dyno allows one to apply a pre-set load to allow the piston rings, and other components to seat properly. It is also much easier to monitor temperatures and pressures than while driving. Most dynos are equipped with O≈ and EGT probes to aid in tuning. The timing and fuel curve needs to be tailored to your particular engine to ensure the engine stays out of detonation, which will lead to engine failure. A racing engine is generally built with sufficient clearance to require no further break-in after dyno tuning and power runs. However, we recommend head bolt torques be re-checked cold after dyno testing as the head gaskets will take a set. Remember to replace oil and filter after the dyno session as bearing coatings and metal particles will be trapped in the oil filter. Inspect the oil for foreign material and excessive bearing flakes.
A street engine should be driven moderately for the first thousand miles, as follows:
- full throttle high torque power useage should be limited and never be used until the engine has been running for at least 15 minutes.
- from 0-500 miles, do not exceed 4000 rpm.
- from 500-1000, do not exceed 6000 rpm.
- over 1000 miles, no restrictions.
Also, do not run at the same speed for extended periods during break-in. Make certain the engine is operating at proper coolant temperature and oil pressure. Do not allow the engine to overheat. Make necessary changes if required (radiator, fan, tuning) to get the engine to run in the proper temperature range. We also recommend you do not run synthetic oil until at least 5000 miles. Synthetics work so well that the engine will never break in properly if it is used too soon.