CAUSES OF ENGINE BEARING FAILURE

CAUSES OF ENGINE BEARING FAILURE
The aim of this manual is to enable the reader to diagnose the causes of engine bearing failure through visual inspection of the bearings. Depending upon the type of failure detected, recommendations are then given as to how to remedy the specific cause of damage. One has to keep in mind here that, in addition to ascertaining the appearance of damaged bearings, accurate diagnosis will necessarily call for further information both on the other components involved and on the precise operating conditions. A summary of the most common causes of bearing failure is provided below, although some failures will inevitably result from a combination of more than one cause.

1 -- DIRT
DIRT IN THE LUBRICATION SYSTEM
DIRT ON BEARING BACK

2 -- OIL STARVATION
MALFUNCTION IN THE LUBRICATION SYSTEM
OIL SEAL FAILURE

3 -- MISASSEMBLY
BEARING REVERSED
REVERSED CON-ROD OR BEARING CAPS
LOCATING LUGS NOT NESTED

4 -- IMPROPER MACHINING OF COMPONENTS.
IMPROPERLY GROUND HOUSING (FACETED OR POLYGONAL)
FILLET RIDE
OUT-OF-SHAPE JOURNAL: HOUR-GLASS SHAPED, BARREL
SHAPED OR TAPERED
MISALIGNMENT OF SHAFT AND HOUSING
INSUFFICIENT CRUSH

5 -- OVERLOADING

6 -- CORROSION

7 -- CAVITATION


1 -- DIRT
DIRT IN THE LUBRICATION SYSTEM
The presence of dirt particles entrained in the lubrication system is one of the most frequent causes of bearing damage. The root of the problem is usually that the engine is not sufficiently clean. In line with the nature and size of the foreign particles, the bearing will exhibit a correspondingly lesser or greater degree of circumferential scratching and, usually, any debris that may have become
embedded in the lining.
Recommendation: when repairing the engine, ensure that the entire lubrication system is carefully cleaned.

-- DIRT
DIRT ON BEARING BACK
The presence of a foreign particle trapped between the bearing back and its housing will lead to a raised area, with the ensuing risk of contact between this protruding high-spot and the journal. Signs of this will be seen in the area opposite the particle, along the inner surface of the bearing, where there will be evidence of marked localized wear.
Recommendation: ensure that all housings in which bearings are to be seated, are carefully cleaned prior to assembly.

2 -- INSUFFICIENT LUBRICATION
MALFUNCTION IN THE LUBRICATION SYSTEM
A total absence of lubrication of the journal-bearing system leads to bearing seizure and, normally, to total destruction of the part. However an altogether more frequent phenomenon is fatigue due to oil starvation, whereby the amount of oil reaching the journal-bearing system is insufficient to maintain the oil film, leading to metal-to-metal contact between the two parts. Prolonged operation under such
conditions will also result in total destruction of the whole.
Recommendation: the lubrication system must be thoroughly checked in order to pinpoint the cause of failure, which may be a blocked oil passage, an improperly installed bearing, an oil pump malfunction, etc.

2 -- INSUFFICIENT LUBRICATION
OIL SEAL FAILURE
In the example shown in the photograph, the failure of the crankshaft seal led to oil escaping at this point The track of the pair of bearing shells nearest the seal exhibits symptoms of seizure, due to the oil film rupturing as a result of loss of oil pressure. The circumferential oil groove acted as a barrier to the defect, so that the other track of the bearing shells, as well as the two remaining pairs in the set, only exhibit shiny areas, a sign of oil starvation.
Recommendation: check for possible loss of oil at the seals and replace these wherever necessary.

3 -- MISASSEMBLY
BEARING REVERSED
Where a bearing having no oil hole is mistakenly fitted in a position in which it ought to have one, e.g., in a case where the upper and lower seats of a pair of main bearing shells are inadvertently switched, this effectively prevents that particular main journal receiving lubrication. As a consequence, no lubrication can reach the crankpin via such oil holes, eventually leading to seizure of the bearing in question. From the bearing back, it will be evident that the oil passage hole has
been blocked off.
Recommendation: ensure that the utmost precaution is taken during the installation of new bearings and that the correct positioning of each is doublechecked.

3 -- MISASSEMBLY
OTHER ASSEMBLY ERRORS
When engines are being repaired, the following assembly errors tend to occur fairly often. There will be areas where lubrication may be insufficient, with evidence of excessive localized wear.
Recommendation: ensure that each and every engine component is correctly installed.

4 -- IMPROPER MACHINING OF COMPONENTS.
IMPROPERLY GROUND HOUSING (FACETED OR POLYGONAL)
Where a housing bore becomes flawed due to engine vibration or some other cause that gives rise to marked out-of-roundness, the bearing will tend to conform to the defective shape of its housing. It will display alternating bands of heavy and normal wear. This defect can lead to metal fatigue.
Recommendation: check for correct grinding of shaft and housing.

4 -- IMPROPER MACHINING OF COMPONENTS.
FILLET RIDE
If the radius of the fillet is increased during the course of a repair to the crankpin, the edge of the bearing may make metal-to-metal contact with the fillet, and will also hinder oil flow. In the photograph, the bearing exhibits signs of incipient damage, with its edge rounded from rubbing against the fillet.
Recommendation: use a grindstone in perfect condition to achieve correct crankshaft geometry.

4 -- IMPROPER MACHINING OF COMPONENTS.
OUT-OF-SHAPE JOURNAL: HOUR-GLASS SHAPED, BARREL SHAPED OR
TAPERED
If the grindstone suffers from excessive wear, the crankshaft will conform to its errors of shape. This means that the clearances and, by extension, the load distribution will not be the same throughout the bearing surface, thereby accelerating bearing wear in the most highly loaded regions due to uneven and inadequate lubrication. Journals can be found with areas that are partially hourglass shaped, barrel shaped or tapered. Visible in the figure is a damaged bearing that has been mounted on a partially tapered journal.
Recommendation: use a grindstone in perfect condition to achieve correct crankshaft geometry.

4 -- IMPROPER MACHINING OF COMPONENTS.
MISALIGNMENT OF SHAFT AND HOUSING
There are a number of causes that give rise to misalignment of the crankshaft and cylinder-block housings, such as improper machining, bent crankshaft, distorted cylinder block, etc. These defects result in localized wear, which tends to be greatest on some of the main bearings and less pronounced on others.
Recommendation: ensure that cylinder-block and crankshaft machining tolerances are in accordance with the engine manufacturer’s specifications.

4 -- IMPROPER MACHINING OF COMPONENTS.
INSUFFICIENT CRUSH
Total contact between the bearing back and housing is fundamental to ensure good heat transfer and a correct seating of the part. If crush is insufficient, the bearing will move back and forth within the housing and shiny areas will be visible on the bearing back due to friction with the housing. On other occasions, discolorations or stains may appear, evidence of burnt oil that has worked its way into the space between the two surfaces.
Recommendation: ensure that the size of the housing bore and torquing are in accordance with the manufacturer’s recommendations.

5 -- OVERLOADING
Where operating conditions cause excessive load to be exerted upon the bearings, this leads to damage due to metal fatigue
Recommendation: check that the assembly clearances and bearing material are as specified for the application in question. Similarly, ensure that engine-tuning conditions are respected.

6 – CORROSION
Oil in poor condition can damage the bearing surface. This effect is due to dilution of the lead in the alloy by certain of the compounds produced by oil degradation.
Recommendation: always use the oil recommended by the manufacturer, and perform the scheduled oil changes as indicated in the vehicle maintenance manual.

7 -- CAVITATION
Under certain operating conditions, oil pressure drops locally, producing vapour bubbles that cause damage to the bearing surface. This damage will be evident in certain bearing areas, such as oil grooves or holes, that are affected by discontinuities in the oil flow.
Recommendation: check that lubrication conditions, such as oil pressure, flow rate and type, are as stipulated by the vehicle manufacturer.

SUORCE:

Cetane Number – What it is and Why it’s so Important

Cetane Number – What it is and Why it’s so Important

Cooperative Fuel Research Engine (CFR)

Cetane is a measurement of a diesel fuel ignition and or combustion quality. This Cetane Number or CN is one of several components that determine the quality of diesel and biodiesel fuels. This number is used for light and middle distillate fuels. For heavy (residual) fuels Calculated Ignition Index (CII) and Calculated Carbon Aromaticity Index (CCAI) are used.
In some ways this measurement is similar to the Octane Ratings given to gasoline. In its simplest terms Cetane Number measures the delay between the start of fuel injection into the combustion chamber and the beginning of compression ignition (Auto-ignition).
In medium and high speed diesel engines (this all automotive and truck engines) fuel needs to have a CN between 38 and 55 to operate. In general the higher the CN number, the better for the engine and for emissions. However raising CN above 55 currently offers little if any benefit.
In the US the group setting the standards for CN is the American Society for Testing of Materials (ASTM) and currently the minimum is 40. While diesel engines will start and run with 40 CN fuel, they do not run as efficiently as they will at a higher number.
In Europe the European Union (EU) has systematically over several years raised the minimum from 38 to the current 51. This has allowed engine manufacturers to produce more efficient engines with lower emissions and better economy. Most fuel in the EU has a CN of 55 or even better.
Cetane Number is measured using a very expensive and arcane Cooperative Fuel Research (CFR) engine and a process that very complex.
You can also measure CN using an Ignition Quality Tester (IQT) which is somewhat less complex, but still quite costly.
There is a third measurement called Cetane Index (CI) that measures density and distillation range of the fuel and through a calculation provides a measurement. This method will calculate a reasonably accurate number for the refined diesel.
The problem is that today most diesel fuel uses additives to reach the desired Cetane Number and additives do not affect the density, thus the CI of a fuel containing additives is not accurate.
Some of you may have seen a device that looks like a battery fluid tester (a hydrometer). These devices are not capable of determining CN or CI with any accuracy.
You can raise CN by altering the refining process or through the use of Alkyl nitrates or di-tert-butyl peroxide additives. NOTE: Remember that additives do not raise CI.
Also, biodiesel, depending on the base oil from which it is derived has a natural Cetane Rating of 46 to as high as 60.
With the advent of Pilot or Multiple Pulse fuel injection, Cetane Number becomes more important than ever. The delay in auto-ignition (CN) affects the combustion timing, which has a significant effect on power output, fuel economy, and emissions.
Raising Cetane Number together with Improving Fuel Atomization is the fastest way to improve fuel economy and reduce emissions through the use of correctly formulated additives.

More information at: http://www.lcbamarketing.com/ - Click on Fuel School Articles.

Diesel Doctor - Copyright 2009© - William Richards

SOURCE:

http://fuelschool.blogspot.com/2009/03/cetane-number-what-it-is-and-why-its-so.html

Valve rotators

Benefits of valve rotators

Each time a valve opens, the valve rotator turns the valve slightly. This prevents the valves sticking due to carbon build up. Additionally, it allows the inlet and exhaust valves to be heated and cooled symmetrically.

Fitted to the top or bottom of the valve spring, the valve rotator helps to keep valves cleaner, reducing carbon build-up and so lowering engine emissions – as well as extending the life of key engine and valve gear components.

Valve rotators help to reduce the amount of carbon deposits on the valve and prevent carbon build-up on the valve seat. Cleaner valves reduce engine emissions and prevent burning and guttering of the valve face and seat. Valve rotators reduce thermal gradient and stress, reducing the need for high-cost nimonic steel valves.

Our rotators are easy to replace during engine service and allow longer engine service interval, extending the life of key engine and valve gear components.

SOURCE:

http://www.helical-technology.com/valve-rotators/benefits-of-valve-rotators/

Multi-valve engines

History
Multi-valve engines started life in 1912 on a Peugeot GP racing car. It was then briefly used by the pre-war Bentley and Bugatti. However, mass production on road cars came as late as 1970s - Ford Escort RS1600 (1970), Triumph Donomite Sprint (1973), Chevrolet Cosworth Vega (1975), Lotus Esprit (1976), Fiat 131 Abarth (1976) and BMW M1 (1979) were the earliest adopters.

Triumph Donomite Sprint was one of the earliest road cars to feature multi-valve technology. Its 2-liter four-pot engine featured 16 valves but just one camshaft, unlike the DOHC designs popular on contemporary racing engines. The intake valves were driven directly by the camshaft, while the exhaust valves were driven by the same camshaft through rocker arms. Today, Honda's SOHC 16-valve engines still employ the same design.

By the mid-1980s, 4 valves per cylinder virtually became standard on high-performance cars, such as Ferrari 308 GTB Quattrovalvole (1982), BMW M635CSi (1983), Ferrari 288 GTO (1984), Mercedes 190E 2.3-16 (1984), Saab 9000 (1984, also the first to combine 4-valve and turbo on production car), BMW M5 (1985), Ferrari Testarossa (1985), Lamborghini Countach QV (1985) and Volkswagen Golf GTi 16V (1985), let alone those Group B rally specials.

However, it was the Japanese who came first to put multi-valve technology on mass production cars that everybody can afford. Honda Civic adopted 3-valve engines as standard in 1983 and 4-valve engines in 1987. Toyota mass-marketed its high-performance 1.6-liter 16V engine on Corolla coupe / Truneo (1983) and MR2 (1984), then equipped the bread-and-butter Corolla with 4-valve engines in 1987. They standardized multi-valve engines nearly a decade earlier than Western car makers !

Advantages and Disadvantages
Multi-valve engines have mainly 3 advantages. Firstly, it increases the coverage of valves over the combustion chamber, allowing faster breathing thus enhance power at high rev. Secondly, it allows the spark plug to be positioned in the center of combustion chamber, enabling quicker flame propagation, more even and more efficient burning. Thirdly, using more but smaller valves instead of two large valves means lower mass for each valve. This prevent the valves "float" from its designed position at very high rev, thus enabling the engine to rev higher and make more power as a result.

A comparison of the 4-valve head on BMW M3 V8 and the 2-valve head on Chevrolet small-block V8 finds the former has larger percentage of area covered by valves. The spark plug is positioned centrally in the 4-valve head, unlike the case of 2-valve head.

On the downside, multi-valve engines use more components, thus they carry more weight and higher costs. While these disadvantages can be largely overcome by mass production, another problem took some years to solve. The early multi-valve engines were not renowned for tractability. At low to medium rpm they actually produced less torque than the equivalent 2-valve engines. Why? Because the larger valve area resulted in slower air flow in the intake manifold. At low rpm, the very slow air flow led to imperfect mixing of fuel and air, resulting in knocking and reducing power. For a racing car or sports car, that might not be a big problem, but for regular passenger cars the lack of tractability is deemed to be unacceptable.

Solutions
Toyota T-VIS
In response to the aforementioned drawback, Toyota introduced T-VIS (Toyota Variable Intake System) in the mid-1980s. T-VIS accelerated low-speed air flow in the intake manifold. The theory was quite simple: the intake manifold of each cylinder was split into two separate sub-manifolds which joint together near the intake valves. A butterfly valve was added at one of the sub-manifolds. At below 4,650 rpm the butterfly valve remained closed so to raise the velocity of air flow in the intake manifold. As fuel was injected at this section of manifold, better air-fuel mixing could be obtained. At high rev, the butterfly opened to allow maximum air flow.

 

The T-VIS was used on performance models like AE86, MR2 and Celica. However, for its mainstream passenger cars, Toyota dropped this feature and adopted a small-diameter intake manifold/port design for cost reasons. Many other car makers went the same way, sacrificing a bit top-end power for better low-speed tractability.

Modern Approaches
In recent years, the low-speed tractability problem can be dealt with a variety of solutions, such as variable intake manifold (which boosts low-end torque), variable valve timing (which may delay the opening of intake valves at low rev to accelerate air flow) and variable valve lift (which varies degree of lift hence air flow speed). However, the ultimate solution must be direct fuel injection. Fuel is now injected precisely into the combustion chamber rather than the intake manifold. Complete vaporization is realized by the high-pressure injector as well as swirl effect.

Number of Valves
3-valve engines
The earliest mass production multi-valve engines were 3-valves because of its simple construction - it needs only a single camshaft to drive both intake valves and the exhaust valve of each cylinder. Today, there are still some low-end cars using this cheap but less efficient design.

Surprisingly, Mercedes-Benz reverted from 4-valve to 3-valve technology on its modular V6 and V8 family in the late 1990s to mid-2000s. The change was not due to cost reasons, but the need for cleaner emission. Research done by Mercedes found great difficulties to comply with the cold-start emission limits required by forthcoming EU standards. By halfing the number of exhaust valves, the surface area of exhaust ports and manifolds can be largely reduced. This reduces the time taken to heat up the catalytic converter at cold start. With the advancement of emission control technology in the coming years, Mercedes eventually abandoned the 3-valve approach.

4-valve engines
Today, by far the majority of multi-valve engines employ 4 valves per cylinder.
Most 4-valve engines employ twin-cam (DOHC) for its obvious benefits, for instance, cross-flow intake/exhaust, low inertia and friction, and the allowance of independent intake and exhaust variable cam phasing. However, some cost-conscious engines (most by Honda and Mitsubishi) still employ single-cam (SOHC) to drive all valves. Like the aforementioned Triumph Donomite Sprint, these engines use rocker arms to transfer the motion from camshaft to exhaust valves. The resultant higher friction and inertia hampers revvability, but it does not matter for applications on family cars.

5-valve engines
Yamaha was the expert of 5-valve technology. Since the mid-1980s it had been using 5-valve technology on its high-performance motorcycles. In 1991, it helped Toyota to produce a 1.6-liter 20-valve engine for Corolla Levin (Trueno). This was perhaps the earliest 5-valve application on road cars. Closely followed that were Bugatti EB110 and LCC Rocket (powered by Yamaha bike engine). Meanwhile, having used 5-valve technology successfully in F1 cars, Ferrari applied it to F355 and F50. However, the only manufacturer ever put it to mass production was Audi (which also benefited Volkswagen group). For about a decade, most engines produced by Audi were equipped with 5-valve heads.

The 5V cylinder head of Audi. Audi devoted its production engines to 5V technology from the mid-1990s to mid-2000s, including the highly popular 1.8-liter 20V, 2.8 / 3.2-liter 30V V6 and 4.2-liter 40V V8.

All 5-valve engines have 3 intake valves and 2 exhaust valves per cylinder, still arranged as cross-flow. The exhaust valves are larger, but in terms of total area intake valves is larger. The intake valves do not necessarily open at the same time. For example, on Ferrari F355, the outer intake valves opened 10° earlier than the middle valve. This created swirl, enabling better air/fuel mixing, hence more efficient burning and cleaner emission.

In theory, 5 valves per cylinder may offer larger valve area than 4-valver for better breathing. The smaller and lighter intake valves also enable the engine to rev higher without worrying of "valve floating". The latter reason was especially crucial to high-revving superbike engines and racing motors. However, the overall advantage of 5-valve technology over 4-valver has always been arguable, because it involves more components hence more mass and friction. Cross-flow breathing is also less ideal than in the case of 4-valver. In 1993, Ferrari gave us a preliminary answer: its F1 motor returned to 4-valve heads. This was made possible as new pneumatic valve springs could solve the "valve floating" problem. In the road car department, Ferrari replaced the 5-valve 360 Modena with 4-valve F430 in 2005 and still capable of making more horsepower per liter. This broke the legend of 5-valve technology. By the mid-2000s, Audi started reverting to 4-valve engines as well, ending the short-lived fever of 5-valver.

6-valve or more ?
Until now, anything more than 5 valves per cylinder is still a dream... a wild dream actually.

In 1985, Maserati announced this V6 engine with a total of 36 valves. The engine coupled to light-pressure twin-turbo to produce 261 horsepower... from just 2 liters of displacement ! Unfortunately it was cancelled before reaching production.

NR750, Honda's GP motorcycle in the early 1990s, even featured 8 valves each cylinder ! Interestingly, the piston was in oval shape to accommodate all valves. It also needed two con-rods to support. In fact, the V4 engine was actually a V8 with each of the two adjacent cylinders combined - just to take the racing regulations' loophole that banned more than 4 cylinders.

Copyright© 1997-2011 by Mark Wan @ AutoZine

FUENTE

http://www.autozine.org/technical_school/engine/Multivalve.html