ABOUT THE ENGINE BEARING

WHAT ARE BEARINGS?Bearings are devices used to transmit loads between relatively moving surfaces. Bearings are used in all types of machinery, engines and mechanisms for supporting and controlling the motion of the rotating, sliding or reciprocating parts. Shafts, spindles or axles usually support the rotating parts. Bearings are designed to serve the purpose with minimum friction, power loss, and generation of heat and are aided in their requirement by suitable lubricants. Bearings are used in Automotive, Industrial, Agricultural, Earth Moving, Marine and Stationary Engines among others. Bearings that support the rotating shaft in a fixed position against loads acting perpendicular to the axis of shaft only are called Radial Bearings. Those that support against loads parallel to the axis of the shaft are called Thrust Bearings, while those, which resist both radial and thrust loads are called Angular or Radial-Thrust Bearings. Bearings are of two types: u u Anti-Friction Bearings Sleeve Bearings

ANTI-FRICTION BEARINGS:These Bearings utilize Rolling Balls or Rollers to provide a Rolling Contact between the surfaces. In an automobile, anti-friction Bearings are found in the Suspension, Transmission and other parts of the Drive Train.

SLEEVE BEARINGS:The Sleeve Bearings are so called because they are shaped like a Sleeve and are firmly held in place around a rotating Shaft, which results in a Sliding Contact. Sleeve Bearings are found inside the Engine i.e. Components like Crankshaft, Connecting Rod and Camshaft.

Sleeve Bearings are also called Insert Bearings because of the manner in which they are installed inside the engine.

TYPES OF ENGINE BEARINGS:Insert Bearings are manufactured in two basic configurations: u u Full Round Insert Bearing Split Insert Bearing

FULL ROUND INSERT BEARING:The one piece full Round Insert Bearing is used where it is possible to insert the Bearings into place between the moving Engine part And the stationary Bearing Housing. Camshaft Bearings are the Full Round types because the Camshaft can pass through the inside of the Bearing.

SPLIT INSERT BEARING:The Split insert Bearings must be assembled around the component because the design of the component does not allow full round type of Bearing. Crankshaft and Connecting Rod Bearings belong to this category. These Bearings are held in place by a Bearing Cap that holds the whole assembly together.

FUNCTIONS OF ENGINE BEARINGS:Insert or Engine Bearings serve three important functions in an engine: u u u Reduce Friction between moving surfaces To support the moving parts of an engine To serve as a replaceable wear surface

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u Reduce Friction Between Moving Surfaces :Experiments have shown that dissimilar material against each other with less friction and wear than similar materials. Thus, a Bearing made out of Copper, Aluminum, Tin or Lead alloy does a better job of reducing friction between steel parts than a steel bearing would. Also, the friction reducing capability of an insert Bearing depends on the addition of a Lubricant between the moving part and the Bearing surface. In fact, a major objective of Bearing Design is to establish and maintain a film of Lubricating Oil between the Surfaces.

u To Support Moving parts of an Engine :The second function of an engine Bearing is to support the moving engine parts of an engine. This means that the Bearing must be able to stand up to the heavy loads placed on it during engine operation and still allow the moving parts to operate freely.

u Serve as a Replaceable Wear Surface :The third function of an engine Bearing is to serve as a replaceable wear surface between the moving engine parts. Although, the use of dissimilar metals and a film of lubricating oil serves to reduce the friction between the moving engine parts, some wear may still occur during engine operation. In this case, it is more economical to replace the low cost bearing than it is to replace expensive major engine components.

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CHARACTERISTICS OF A BEARING ALLOY:A Bearing Alloy must have certain characteristics in order to perform the intended function satisfactorily. These are listed below: u u u u u u u u u Load carrying capacity Fatigue Resistance Embedability Conformability Corrosion resistance Compatibility Temperature Strength Thermal Conductivity Wear Rate

u LOAD CARRYING CAPACITY : Modern engines are Lighter and more Powerful. They have Higher Compression Ratios, which impose greater loads on the Bearings. Hence, Bearings must be able to withstand these loads. Today, Connecting Rod Bearings carry loads with a minimum value of 6 000 psi (41 369 kpa). u FATIGUE RESISTANCE: This signifies the ability of a bearing material to withstand the loads during engine operation. A bearing material must be strong enough to support the loads the bearing is subjected to during engine operation.

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u EMBEDABILITY: This term refers to the ability of the bearing material to permit foreign particles to embed in it. Dirt and Dust Particles enter the engine despite the air cleaner and oil filter. Some of them work onto the bearings and are not flushed away by the oil. A Bearing protects itself by letting such particles sink into, or embed in, the bearing lining material. These particles can disrupt the oil film, creating localized Hot Spots on the bearing surface resulting in fatigue failure of the Lining. u CONFORMABILITY: This is the ability of the Bearing material to variations in Shaft alignment and journal shape. E.g. a shaft is slightly tapered. The bearing under the larger diameter will be more heavily loaded. If the bearing material has High Conformability, the material will flow slightly, from the heavily loaded areas to lightly loaded areas. This slight flow evens the load on the Bearing. u CORROSION RESISTANCE: The by-products of combustion may form corrosive substances, harmful to some metals. Unleaded Gasoline, required on cars using Catalytic Converters, changes the chemistry of the oil, resulting in an increase in Bearing Corrosion. Aluminum-Lead Bearings withstand corrosion better than Copper-Lead Bearings. u COMPATIBILITY: Compatibility is the ability of the Bearing Lining material to operate with a dissimilar metal and not suffer any Structural Damage.

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u TEMPERATURE STRENGTH: Many materials are unsuitable for use as a Bearing material as they tend to Loose their hardness i.e. become Ductile at elevated temperatures. Hence, Bearing material should have good temperature Strength. u THERMAL CONDUCTIVITY: This signifies the ability of the Bearing material to absorb and Dissipate Heat since a great amount of heat is generated by the load and speed of the rotating shaft. u WEAR RATE: The bearing material must be so hard and tough that it will not wear too fast. At the same time, it must be soft enough to permit good Embedability and conformability.

ALLOYS USED IN BEARINGS:If Lubrication were always perfect and bearing surfaces fitted accurately so that running in was unnecessary, then almost any metal would suffice as a bearing material provided it was capable of carrying the load. In fact, it is often difficult to align a long shaft accurately enough to run in a series of bearings. Consequently, a relatively soft, malleable material is used so that it will align itself to the journal when under pressure. This prevents the build up of stress at any High Spots on the surface so that journal is less likely to be scored by grit in the Lubricant. Nevertheless the bearing material must be strong and hard enough, preferably with a low-friction, wear resistant surface. This set of properties is generally not obtained in a single-phase alloy. Hence, bearing metals have been two-phase alloys, e.g. White metals and Bronzes. In these materials, Harder, Low-Friction particles are held in a malleable, soft solid solution (or eutectic) matrix. Bearing materials are of three main types:

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u Two phases alloys of the traditional types, viz. White Metals and Bronzes. u Two-phase alloys in which one phase can become a lubricant under extreme circumstances, e.g. Leaded Bronzes and Aluminum based alloys. u Single Phase materials, (Polytetrafluoroethylene). e.g. Nylon and PTFE

u TWO PHASE ALLOYS VIZ. WHITE METALS AND BRONZES:

WHITE BEARING METALS:These may be either Tin based or Lead based. Tin based Bearing alloys are better quality Bearing alloys and often called Babbit metals, after Isaac Babbit, their original patentee. All of these alloys contain between 3.5% and 15.0% Antimony, much of which combines with some of the Tin present to form an intermetallic compound SbSn. This compound forms cubic crystals which are Hard and of Low-Friction properties. Tin based Babbit of the earliest bearing materials developed consisted of approx. 89% tin, 7.5% antimony and 3.5% copper. Lead Based bearing alloys is cheaper than tin based alloys. These Lead rich alloys are used only for low-pressure applications. Lead based Babbit contains approx. 83% lead, 15% antimony, 1% arsenic and 1% tin. Lead based Babbit alloys are less resistant to corrosion than tin based Babbit. Although its Fatigue Strength is not as high as other Bearing materials, Babbit offers good Embeddability and Conformability.

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u COPPER BASED BEARING ALLOYS I.E. BRONZES: These can be further subdivided into two categories: u u Over-plated Copper Lead Bearing Alloys Non over-plated Copper Lead Bearing Alloys

u OVER-PLATED COPPER LEAD BEARING ALLOYS: These materials are used in Bearings required for Heavy Duty and Extra Heavy Duty Applications. It is of Five-layer construction. High fatigue Strength in this bearing alloy is achieved by limiting the amount of lead in the copper-lead Lining to less than 30%. Actually, this alloy contains only 24% lead, 1% tin and remaining 75% copper. The over-plated copper-lead bearing also provides good conformability and Embeddability, plus excellent corrosion-resistance and thermal conductivity. u NON OVER-PLATED COPPER-LEAD BEARING ALLOYS: This alloy contains 65% copper and 35% lead. It is classified as a Medium duty Bearing alloy because its higher lead content makes it somewhat softer than the Over-plated Copper Lead Bearing alloy. Its higher Lead content also eliminates the need for an over-plated layer.

FUNCTION OF LEAD IN THESE BEARINGS:Should Lubrication fail, the lead is extruded under pressure, as overheating sets in, and forms a lubricating film which prevents Seizure.

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u ALUMINIUM BASED ALLOYS: Aluminium based Bearings are further classified into three types: u u u Non over-plated Aluminium Tin alloy Non over-plated Aluminium Lead alloy Over-plated Aluminium Cadmium alloy

u NON OVER-PLATED ALUMINIUM TIN ALLOY: This bearing alloy consists of 79% Aluminium, 20% tin and 1% copper. This is a medium duty-bearing alloy. Aluminium has excellent load carrying capacity. Tin is added to make it compatible with finished crankshaft surfaces. u NON OVER-PLATED ALUMINIUM LEAD ALLOY: This alloy is also a medium duty-bearing alloy and its composition is 89.5% aluminum, 6% lead, 4% silicon and 0.5% tin. Lead also plays the same role in Aluminum lead bearings as is played by tin in tin lead bearings. Both these types of bearings provide good fatigue strength, high thermal conductivity, excellent corrosion resistance and good compatibility.

u OVER-PLATED ALUMINIUM CADMIUM ALLOY: This is a Heavy duty and extra Heavy duty-bearing alloy. It is of four-layer construction. Bonded onto a steel back is an aluminum-cadmium alloy lining with a lead tin over-plating all over. A nickel barrier plate as found in over-plated copper-lead bearings, is not necessary in this bearing, since the over-plate is not reactive with the aluminum lining material. As an9

Aluminum alloy, this bearing material features superior resistance to corrosion from organic acids. It also offers outstanding service life. The aluminum-cadmium alloy consists of 95% aluminum, 3% cadmium and 1% each of copper and nickel. u SINGLE PHASE BEARING MATERIALS: In this category, Nylon and PTFE (Polytetrafluoroethylene) are the most important. The coeff. Of friction of PTFE ( =0.03-0.1) is lower than for any other solid material. However, to improve its mechanical properties, it has to be strengthened by some Filler material. PTFE/Bronze Composites are used up to temperatures of 300C--The upper working limit for PTFE. They are used in automobile industry as Bearings in Windscreen Wipers and Steering System Bushes. For Nylon, Bronze can be used as the Filler material. An important feature of both materials is that they function well as Dry Bearings. Hence, they are useful in machinery for the preparation of food and textiles where contamination by a lubricant would be unacceptable. They are also used in some cases where a bearing is so inaccessible as to make its lubrication difficult.

ALLOYS USED IN GABRIEL E.B.D: Following alloys are used in Gabriel for bearing manufacture: u BRONZES: HF 2 HF 16 80.0% Cu, 10.0% Sn, 10.0% Pb (ISO CuPb10Sn10) 72.0% Cu, 3.5% Sn, 23.0% Pb 3.0% max Zn (ISO CuPb24Sn4)

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u OVER-PLATED COPPER: HF 24 74.5% Cu, 24.5% Pb, 1.0% Sn (ISO CuPb24Sn)

u ALUMINIUM ALLOY: AT 20 AL 6 An 79.0% Al, 20.0% Sn, 1.0% Cu (ISO AlSn20Cu) 89.5% Al, 6.0% Pb, 4.0% Si, 0.5%

On the next page is a table showing comparison of important parameters for some common bearing alloys as per FEDERAL MOGUL specifications. Entries are on a scale of 1 to 100. FEDERAL MOGUL specs H 116 A 250 H 24 A 200 AT 20 Bearing Material Over-plated Copper Lead Over-plated Aluminium Tin Over-plated Copper Lead Over-plated Aluminium Alloy Un-plated Aluminium Tin Load Conform Embeda Corrosion Compati Capacity --ability --bility Resistance ---bility C with soft ost shafts 100 100 85 75 60 85 80 85 80 60 85 80 85 80 60 90 100 80 100 100 No No Yes Yes Yes 90 100 90 100 75

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H 35 LT B 100 L 100

Un-plated Copper Lead Tin base Babbit Lead base Babbit

50 25 25

70 95 100

70 95 100

60 100 70

Yes Yes Yes

70 85 65

HOW AN INSERT BEARING WORKS:Engine Bearing requires a film of lubricating oil to be present between the bearing surface and the moving part. This reduces friction. The working of the Bearing is explained in detail below: When the engine is at rest, the engine lubrication system is not supplying oil to the oil clearance space, and the non-rotating shaft is resting on the bearing surface. When the engine starts, the rotation of the shaft will cause it to climb up the surface of the bearing. However, at the same time, the engine lubrication system will begin to supply oil to the oil clearance space. The rotation of the shaft combined with the introduction of oil will cause a wedge to be formed between the shaft and the bearing. As the rotating shaft continues to climb the bearing, the wedge effect of the oil lifts the shaft off the bearing surface and allows the oil film to flow under the shaft and completely surround it. As the shaft continues to rotate, and the oil clearance space receives a constant oil supply under pressure, the shaft will rotate on a continuous film of oil.

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ENGINE OIL: As is evident from the foregoing discussion, Engine oil plays an important part in the smooth functioning of the engine. Engine oils are carefully formulated to reduce the adverse effects engine operation. Effective engine oil should possess following important properties: u u u u u u u Prompt circulation through the engine circulation system. Provide lubrication without foaming. Reduce friction and wear. Prevent rust and corrosion Prevent the formation of Sludge and Varnish deposits Provide cooling for engine parts Keep internal engine parts clean.

TERMINOLOGY OF MAIN AND CONNECTING ROD BEARINGS:Various terms associated with Bearings and their definitions are given below: 1. LINING THICKNESS: Lining Thickness is the final thickness of the lining on the strip. Lining thickness varies with different types of bearing materials, e.g. a Babbit lining would normally be thinner than an Aluminium or copper alloy lining. 2. BACK THICKNESS: Back thickness is the dimension of the bearing without lining material i.e. the steel thickness. Different tolerances are used on the back thickness depending upon the type of material used for lining.

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3.

WALL THICKNESS:

Wall thickness is the combined thickness of the bearing back and the lining material. Wall thickness is determined by shaft size, housing size and desired oil clearance. LENGTH: The length dimension is from one end of the bearing to the other end.5.

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HEIGHT:

Bearing Height is the critical dimension. It is the distance from the parting line surfaces to the top of the bearing crown. Bearing Height ensures that the bearing back is in complete contact with the housing bore surface.

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CRUSH:

When two bearing halves are seated and bolted in the engine, the bearing height provides a crush fit. This ensures that the bearing will remain firmly and properly seated during operations. Crush prevents bearing movement in the housing. CRUSH RELIEF:

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Wall thickness at the parting line of the bearing is reduced for the crush relief. This minimizes the effect of crushing the lining at the parting surfaces into the oil clearance space. Also, Crush relief will also compensate for any slight misalignment or side shift of the bearing cap.

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8.

BEARING SPREAD:

Bearing Spread is the outside diameter of the bearing across the parting surfaces. Its slightly more than the housing bore diameter into which the bearing fits. Spread permits the bearing to shape into place and to remain into place during the engine assembly.9.

GAUGE DIAMETER:

Gauge diameter is equivalent to the height limit of the bearing housing into which the bearing fits. It determines the amount of bearing spread necessary and is used in determining the bearing height. 10.OIL CLEARANCE: Oil Clearance is the space between the bearing and the shaft for the oil to flow. This oil clearance is usually a few thousandths of an inch. 11. DISTRIBUTING GROOVE: The distributing groove or the oil spreader is used to improve axial distribution of the lubricant. This groove is used only on certain wide engine bearings.

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ANNULAR OIL GROOVE:

Annular oil groove transfers lubricant for linear distribution across the surface of bearing. In most automotive and diesel engines, grooved bearings are used in upper main bearings positions.

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13.

OIL HOLE:

Oil hole transfers lubricant to bearing surfaces. In most engines, a main oil gallery in the block feeds lubricant to the crankshaft journals and oil clearance spaces. Therefore an oil hole is required in all main bearings. In con-rod bearings, oil is sent to the bearings through the holes drilled in the con-rod.

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LOCKING LIP or LOCATING LUG:

The locking lip locates the bearing in the housing and prevents the bearing from shifting endwise in the bearing housing during assembly. A dowel also serves the same purpose but is not used frequently. PARTING LINE CHAMFER:

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Chamfer eliminates a sharp edge, which, under the unavoidable slight misassemble conditions, would tend to shear the oil film from the shaft. 16.BEARING UNDERSIZE: When the crankshaft is worn to the extent that standard bearings will result in decrease in oil pressure, then, undersize bearings are used to compensate for additional oil clearance. Though these bearings are thicker, they are called undersize because the journals and crankpins of the crankshaft are smaller in diameter i.e. are under the standard size.

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17.ECCENTRIC BEARINGS: In this type of Bearing, the wall thickness gradually becomes thinner in taper from the crown to the parting faces. Eccentricity has two benefits: u u Slight eccentricity built into the bearing wall helps increase the wedge effect to build the oil film under the loaded area. Eccentric wall bearings allow a reduction of the vertical oil clearance without reducing the effectiveness of the oil flow through the oil clearance space for cooling purposes.

In addition to these terms, some special terms are used for Flange Bearings. These are as follows: THRUST FACE:

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The thrust face controls the crankshaft endplay and absorbs the thrust load resulting

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BEARING LENGTH: Bearing length is the distance between the

outside flanges or faces. BAR GAUGE:

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The inside distance between the flanges of a double flanged bearing is referred to as bar gauge. 321.

FLANGE THICKNESS: Flange thickness is merely the wall

thickness of a flange.

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22.

FLANGE OIL POCKET:

The flange oil pocket is machined into the thrust face of the bearing. Its purpose is to provide lubricant between the thrust face and the crankshaft thrust disc.

BEARING MANUFACTURE:Engine Bearings and Bushings are produced by several different methods, depending on the exact use of the bearing/bushing in the engine.u

Main bearings and Connecting Rod bearings are produced by the Strip Process. In this process, bearing lining is applied to a continuous steel strip. This strip is then cut into blanks and formed into the proper shape. The formed blanks then go through a series of manufacturing steps to produce the finished bearing half. Cam-shaft bearings are produced by two methods: These bearings are manufactured from a seamless steel tube with lining material bonded to the inside. The tubing is then cut into sections and machined as required to produce a finished bearing. For heavy-duty applications, Camshaft bearings are formed out of a rolled, flat steel strip that has a heavy duty lining material bonded to it. The ends of the strip are then joined with either a straight or interlocking seam. Bushings are produced by two methods: Some Bushings are manufactured out of a wrought bronze or a steel strip with a bronze lining sintered to it. The ends of the strip are then joined with an Interlocking Clinch Butt Seam.

u u

u

uu

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u

Some Bushings are cast out of solid Bronze.

Below is given the Process Flow Charts for the manufacture of Straight Bearings, Flange Bearings and Bushes:

PROCESS FLOW CHART FOR STRAIGHT BEARING:BLANKING FORM & COIN FACE & CHAMFER GROOVE FIRST HOLE LIP SECOND HOLE I.D /O.D C DINK NOTCH LIP MILL CORNER CHAMFER I.D BROACH

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PLATING BAKING HEIGHT BROACH

PROCESS FLOW CHART FOR FLANGE BEARING:

BLANKING FLARING COINING COUNTER BORE PRE HEIGHT BAR TURN I.D BORE GROOVE FIRST HOLE LIP PUNCH SECOND HOLE I.D/O.D C SINK LIP MILL I.D BROACH PLATING 20

SHEAR BROACH POCKET MILL HEIGHT BROACH DEBURR

PROCESS FLOW CHART FOR BUSHES:

BLANKING GROOVING I.D/O.D C SINK FIRST FORM SEMI COIN FINAL COIN ANNEALING FACING GRINDING TUMBLING TIN FLASH BORING

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MAJOR BEARING DEFECTS:u BURR : It is a protruding Ragged Metal edge that is raised on the surface of the Bearing during blanking, facing, chamfering, hole punching, countersinking, lip milling, groove milling, I.D Broaching and Height Broaching. Burr is the enemy of the machine and the engineering component. Loose Burr during operation may get detached from the bearing and may get mixed with the lubricating oil thus interfering with the lubricating system of the engine. Hard Burr will remain with the Bearing and would continuously destroy the mating component. Although, the manufacturing process in G.I.L is such that the Burr occurring in one process is removed in the next process, problem of Burr continues after machining and height broaching. Bearings with Burr above I.D, O.D or Parting Line are not acceptable. u BEARING LENGTH: Length of the Bearing if in excess will foul with the Crank side, or Bearing will not fit properly. If the Length is less, itll permit a lot of oil to leak out and decrease the oil pressure.

u LIP PUNCHING: Lip Location, Size and Length in operation in accordance with the recess cut in the housing for the Lip Bearing to sit. Any variation in this dimension would affect proper seating of the bearing in the engine Block. Wall Distortion during the Lip Cutting operation is to be avoided as this will lead to the improper fitment or caving in of the I.D surface inside the Housing and near the lip area, which would in turn foul the Shaft and Bearing may fail or rotate in the Housing. u OIL HOLE LOCATION: Lubricating oil is extremely essential for engine to run. If oil Supply is stopped, Bearing would be dry and shaft will22

generate a lot of heat due to friction, as a result, the engine would seize immediately. Hence oil hole location has to be correct so that it allows continuous oil flow. u FULL GROOVE, GROOVE: PARTIAL GROOVE & DISTRIBUTION

Step in Groove, chattering, back thickness, any variation would cause uneven oil flow and under load oil film breakage. Actually, grooves are provided to collect oil from oil hole and distribute oil in a uniform oil path. Therefore, we see all the post failure bearings show less distress in upper as compared to lower. It is important to maintain groove depth and groove profile without any step and chattering. u WALL THICKNESS (I.D. BROACH): Wall thickness directly affects oil clearance between the shaft and the Bearing. In this process, four defects can occur: 1) Excess wall thickness would reduce the clearance. This increases possibility of shaft to touch bearing surface and reduce oil clearance and cause Engine seizure. Less wall thickness would result in excessive clearance and oil pressure would reduce and increase the possibility of shaft resting on bearings i.e. cap bearing. Oil will also leak from shaft without feeding other parts. Non uniform wall thickness would cause turbulence in oil flow and oil film will tend to break at times allowing the shaft to touch the bearings. Taper in wall thickness will create non-uniform oil clearance and oil flow will be affected.

2)

3)

4)

u NOTE: CRUSH RELIEF: This affects the engine performance the most because this has to several useful purposes. The BI-material effect of23

slight bearing cap shift is minimized so that foreign material in lubricating oil can be more easily expelled and in certain instances, the formation of a sustaining oil film is aided by the extra clearance area. As a result, all cases may lead to premature engine failure. u CRUSH HEIGHT: 1. Low crush would result in instability to the bearing pair. Pair would start flexing (moving) in position and would ultimately rotate. This would cause damage to shaft and housing and engine may seize. Excessive crush would either make bearing buckle in or distort housing cap. If crush is very much in excess a cap would not seat on housing properly leaving a gap between cap and housing surface in all these cases bearing at parting faces would cave inside and would cause failure after some period or if clearances are maintained considering top to bottom diameter, shaft wold touch the bearing sides. Even housing distortion will take place as this would result in more clearances at top and bottom and less at sides. Hence crush should be maintained according to the specifications. Excessive taper in parting line would cause the bearing pair to tilt a little bit thus causing a misassemble and variation in clearance or else one bearing would buckle inside from one portion causing shaft to touch the bearing and resulting in engine failure. Maintain proper taper and check for rock and parting line blue contact.

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u LOW SPREAD: Bearing would tend to cave in after running and would probably touch shaft at sides. Bearing spread would show reduction. Engine. Engine would probably seize. Bearing pair may rotate causing damage to shaft and housing. Spread is to be kept on higher side of tolerance.24