Diesels "Engine Parts #2"

Qualities of A GoodBearing Material?

-Fatigue resistance (most important) -Conformability -Embed-ability -Seizure resistance -Corrosion Resistance

Bearing loads have 3 forces on them:

1. inertia forces of reciprocating parts, 4 strokes reverse 2. gas forces on the piston 3. centrifugal forces on the crankpin created by the crankpin end of the connecting rod.

How do you remove precision shells?

1. remove bearing bolts. 2.remove bearing cap 3. remove top half of precision shell 4. jack up crankshaft, roll out lower bearing precision shell so it is on top.

You take deflection readings every _______ degrees

90. Used to find worn low side main bearings and bedplate misalignment. Deflections are taken by measuring the distance between the crank webs at a place opposite to the crank pin location. Note: because of the interference from the connection rod A&E must be averaged.

forked conrod

A fork and blade connecting rod has a fork and a blade which both attach at a common bearing and have similar rotations.

Micro-seizure

As the piston passes areas of low or missing oil surface the rings will tend to weld self to the cylinder wall, to then tear loose in a process called Micro-seizure. A dull gray surface is an indication of micro-seizure. The bright silver is metal to metal scraping of the liner by rings.

Bearing Failures, Their Causes and Appearance

Below are the major types of bearing failures: Normal Wear. The bearing exceeds the allowable wear limits. If caused by highly abrasive particles, the bearing surface may be deeply scored. Bond Failure. The bearing metal separates from the backing in large chunks. Usually the cause of a manufacturing defect Fatigue failure Wiping. Failures caused by overload and misalignment are similar in appearance, both having a smeared or wiped appearance in the bearing surface. Polishing occurs as a result of journal-bearing contact. If contact is heavier and metal flows, this is known as a surface smear. When a wipe occurs, there is significant metal flow and overheating of the bearing surface. If the wipe occurs at the end of the bearing it is generally caused by misalignment. If the wipe is in the center or across the bearing length it is generally caused by overload. Corrosion. Corrosion is a trigger mechanism in many marine bearing failures. Corrosion failures result from rusting of the bearing shells or housing. Particles of iron oxide are picked up and suspended in the oil, carried to the bearing load zone, scoring the bearing surface and the journal. This type of failure is readily identified by the presence of iron-oxide particles embedded in the bearing surface and by the circumferential score marks or grooves machined in the shaft.

A four stroke has downward pressure during _______ and _______ strokes

Compression and power

Where do you take readings for crankshaft deflections?

Crankshaft deflection readings are taken between the crank webs opposite the crank pin journal. There for the distance between crank webs opposite the crank pin journal.

Fatigue Failure

Fjigsaw atigue. Surface cracks are formed in the bearing surface, giving it the appearance of a jigsaw puzzle. If these cracks complete a path around the grain boundaries of the babbitt, particles of babbitt may come out of the surface in large chunks and precipitate a wipe.

How is the crankhsaft lubricated on med & high speed diesel engines?

Flows through drilled lubricating holes

How does crankshaft lubrication work for For medium and highspeed engine

For medium and highspeed engine oil passages as shown to the right are the most common way of lubrication. Using forced lubrication from the main bearings to flow to the crank pin bearing and then through the connecting rod to the wrist pin if installed oil spray of the piston crown At about 3 to 4 bar pressure

Bearing shell Locks

Hold bearing shell in place so does not rotate in the bearing housing. Thin walled have a notch, thick walled have a dowel

Why do you have to be careful with feeler gauges for measuring bearing wear?

If it breaks off in the bearing, you have to take everything out.

4-Stroke Bearing Loads

In a four stroke engine, maximum bearing load occurs near top dead center at the start of the power stroke, due to the combustion gas forces. The load on the bearing is reversed at the top of the exhaust stroke with an inertia load only slightly smaller than the firing load.

What are hydraulic thrust bolts (jack bolts)?

Jack bolts are hydraulically tightened long studs with incorporated hydraulic connection which holds the upper keep of the main bearing intact. They do not pass through the main bearing keep housing but do hold the keep by using hydraulic tension applied and maintained externally.

A larger bearing surface area means

Less load force. Newer engine designs bolt the piston rod directly to the top of the crosshead pin eliminating the lower piston nut. This allows the lower bearing surface area to be much larger reducing bearing load. Since the combustion forces always act down towards the crankshaft on a two-stroke engine the lower bearing is subjected to the greatest forces.

What are the parts of the Kingsbury thrust bearing?

Leveling plates behind the shoes allow the shoes to assume the proper position to transmit thrust. Note Shoes Upper leveling plates Lower Leveling Plates Base Ring Thrust Ring not shown Leveling plates are used to keep equal continues pressure on the Shoes

What happens if there is too much crush?

Lots of shine, warping

How does newer conrod design reduce piston pin wear?

Newer engine designs bolt the piston rod directly to the top of the crosshead pin eliminating the lower piston nut. This allows the lower bearing surface area to be much larger reducing bearing load. Since the combustion forces always act down towards the crankshaft on a two-stroke engine the lower bearing is subjected to the greatest forces.

What is bearing crush?

Nip. used to get most intimate contact between the outside of the bearing insert with the bearing housing and cap. A properly fitted bearing will protrude slightly above the centerline of the housing bore.

Will gauges help to measure uniform wear on the bearings in the crankshat?

No

Do low-speed diesel engines have oil passages in the crankshaft?

No! the oil is delivered to the crosshead then lead to the crank pin. This lowers the chances of stress cracks developing in the crank.

What are the parts of the crankshaft?

Oil Passages Main Bearing Journals Crank web Crankpin journals Counterweights

fixed piston pin

Pin is anchored in the piston with the upper end of the connecting rod oscillating about the pin.

Semi-floating piston pin

Pin is clamped to the connecting rod and the pin oscillates within the piston.

Full floating piston pin

Pin is neither attached to the piston or the connecting rod and is allowed to float within the piston and the upper end of the rod. Snap rings prevent pin from contact with cylinder wall.

What causes carbon deposits and pistons sticking to the liner?

Poor combustion

Earthing Device

Prevents pitting on shaft caused by electricity. A turning propeller is electrically insulated from the hull by the lubricating oil film in the bearings. Electrical potential is generated between the shaft and the hull. As a result the cathodic protection of the ship will not protect the propeller. Electrical potential can cause currents in the bearings resulting in pitting of the bearing surfaces. Problems can be avoided if the shaft is earthed with a propeller shaft slip ring. This shaft earthing assembly comprises a pair of high silver content/graphite compound brushes mounted in a balanced brush holder, running on a copper slip ring with solid silver track.

What is the difference between Camshaft Lubricating Oil Systems on older systems?

Separate camshaft lube system. On older engines the lubricating oil could become contaminated with fuel oil within the high-pressure fuel pump. A separate camshaft lube oil system was used on these engines to minimize the amount of contaminated oil that would have to be replaced.

2-Stroke Bearing Loads

Since 2-Cycle engines only have power and compression strokes, bearing loads are in the upper half of the crank pin bearing, and the lower half of the main bearings

Articulated con rod

The articulated type connecting rod has one rod attached to the large bearing and second rod attached to a second smaller bearing.

What is the disadvantage of side-by-side arrangement in a V-Type Engine Connecting Rod Journal Arrangement?

The connecting rod journal must be twice as long to accommodate both connecting rods. An engine constructed in this manner will be much longer than an engine constructed with either the Articulated or Fork & Blade arrangement.

What are the consequences of poor engine chocking?

The consequence of poor initial installation are extremely serious since it may lead to fretting of chocks, the foundation and bedplate, slackening and breakage of holding down bolts and ultimately in a worsening in the alignment of engine.To maintain engine alignment it is important to inspect the bolts for collect tension and the chokes for evidence of fretting and looseness.

Bearing Crush

The force created to seat the bearing by the extra bearing material when the ends of the bearing inserts touch each other and are forced against each other

What is the purpose of chocks on the engine blocks?

The lateral and transverse location is maintained by side and end chocking.The number of side chocks depends upon the length of the engine.

transverse girder

The most highly loaded pat of a bedplate is the transverse girder. The transverse girder acts as a simple beam with the forces of combustion acting on the piston passing down through the bearing. The forces acting on the head are passed through the Tie rods.

Roller thrust bearing

The thrust is transmitted through the bearing to the frame Large area to large area. 1 Shaft thrust 2 Transmitted to frame

Why is Crosshead Lubrication difficult?

The upper connecting rod bearing or crosshead bearing of a slow-speed diesel engine is difficult to adequately lubricate. The bearing has minimal rotary motion and formation of an oil wedge is difficult to achieve.

Cam flank grinding

The way the flanks slop of a cam are ground will affect the rate and speed a cam will open or seat. A sharp angle on the flanks will accelerate the rate of valve opening or closing.

In a typical truck-type piston, what is characteristic about the crown and skirt?

They are either 1 piece of the same material; or even if they are two different materials, they are permanently joined together.

common bearing materials

Tin antimony copper a eutectic mixture - lower melting point. •(Tin Base Babbitt) •Lead tin antimony copper also a eutectic mixture •(Lead Base Babbitt)

Heat Dam

To better control where the flow of heat travels a piston crown.

7 important functions of the bedplate

To support the static load of stationary engine frame and blocks To support the dynamic load of the running gear To support the crankshaft and hold it in perfect alignment To distribute the static and dynamic load generated by running engine onto the ship structure To collect the crankcase lube oil and transfer it to the sump tank from where the lube oil pump can take suction To fasten the engine to the tank top transmitting propeller thrust to the hull structure To contribute to the hull strength of the ship at engine room bottom structure

Piston Ring seating

With chrome rings a brass ring is often inserted in the ring surface to promote seating of the ring. -Highest land wear area is in zone B and can affect the ring also.

How do you adjust the tie rods that hold the frame to the bedplate?

You do them in pairs, Uniform tension is critical

Inspection Schedules for Large low speed engine bearings

a) Connecting rods (top and bottom) bearing clearances, checked every 6 months. b) Main bearing clearances, checked once a year, compared to deflection readings. c) Thrust bearing clearances and pads, checked annually.

What are the factors influencing min Bearing Clearances?

a. bearing material (conformability) b. operating temp range c. accuracy / precision of parts d. oil viscosity, pressure and quantity + effectiveness of filtering system.

Bearings are designed to be loaded ...

all the time.

On a slow speed diesel engine, the crank pin gets lubricated by

articulated arms or telescopic tubes. Oil then travels down the connecting rob to the crank pin. Oil to the main bearings still goes directly to the Main Bearing Journals (however there are no drilled passages in the shaft of a slow speed crank)

On a bearing, Thrust travels from

big to big

How do you find upper main bearing bearing clearances?

can be found using a depth micrometer with a bridge gauge. A close reading can be taken using depth feeler gauges between journal and bearing shell.

Plastigage

carefully designed material that flattens out uniformly when pressed. Small engines only

The camshaft is driven by a __________ or ______ on the crankshaft.

chain or gear

Tie rods

components that hold the bedplate, frame, & cylinder jackets of an engine together.They relieve the bedplate and columns from the combustion (firing) and inertia forces. Rods are under tension placing the bedplate, frame and jacket under compression forces. Remember that bearing bolts (17) must be slack before tensioning tie rods in pairs.

Liner Cracks occur anytime when

cooling water is obstructed or blocked off. Or air is allowed to set in the liner Jacket water area forming hot spots on the liner.

Two stroke always has _______ pressure on it

downward

Not enough crush

dull and worn around leaves, it will cave in.

Positive crankcase ventilation (PCV)

engine crankcase fumes are filtered and drawn into the intake manifold.

Modern crosshead bearings use the ________ ____________ of the crosshead pin as a bearing by _______________________.

entire underside, connecting the connecting rod foot to the top of the crosshead pin.

What type of side thrust is there on a crosshead engine?

from rolling due to wave action, and also scavenge air and or exhaust pressure from the ports.

Backing on precision bearings

hard metal backing of bronze, steel cast iron or aluminum. If aluminum used in bearing then soft aluminum backing.

To lubricate the camshaft, newer engines have redesigned _______ which prevent lube oil _________.

high-pressure fuel pumps , contamination

Never attempt to file the extra shell length down because...

it will create a deformed bearing

The bridge gauge is provided by the

manufacturer

What holds the engine at the top?

mechanical or hydraulic top bracing

Chocks are made of

metal or epoxy resin

Crankshaft deflections

misalignment due to wear / deflection, Indications are bearing wear and bearing temperature increase. Readings indicate: * misalignment of the crankshaft. * a main bearing who's lower bearing shell is more worn than other main bearings * to be taken at 90 deg. angles to give a 360ˆpicture of crank rotation. Reedings will not indicate: *upper main bearing shell wear * Uniform bearing wear * wear of the underside of connecting rod crank pin beating shell

Improper bearing crush can cause:

overheating, rotation of bearing shell in housing

If the piston clearance is too large, what happens?

piston slap!

What is the puncture valve?

puncture valve is fitted in the top cover of the pump. It is opened when compressed air from the control air system acts on top of a piston fitted in the top cover. Fuel oil from the discharge side is then returned to the suction side of the pump and no injection takes place.

common causes of bearing failure

scratched by dirt, lack of oil, improper seating, tapered journal, radius ride, fatigue failure.

A piston crown is usually ______ than the skirt to allow for expansion of the crown when operating.

smaller

Why is there a pre-lube pump on trunk-type diesel engines?

to get the engine started with some lubrication, until the attached or primary lube oil pumps take over. This prevents serious rubbing of piston on cyl liner.

Why was a crosshead booster pump was provided

to increase the crosshead lubricating oil pressure. Older engine designs may have supplied oil to the crosshead at elevated pressures to help lubricate the bearing.

•Most common bearing is the Precession insert bearing made in

two haves lined with Babbitt

Old-style crosshead pins of the old style have ________ bearing surfaces one on_________ of the piston rod nut.

two, either side. Located between the two purple areas.

Crankshaft Counterweights

used to dynamically balance the crankshaft and to position the force needed keep the piston in motion during its cycle. This prevents force used for piston motion from moving along the crankshaft lowering crank shaft stress to that used for power consumption. on slow speed diesels due to the mass are usually built as part of the crank throw and do the same function as bolt on weights.

Piston Rod Seal

used to prevent the products of combustion from entering the crankcase allowing a very ling life for the lubricating oil used. also prevents crankcase oil from getting in the scavenge spaces under the piston.

Why is there taper in a trunk piston?

with side thrust you could get the top outside edge of the crown plowing into or at least scraping the liner. And allows for the anticipated greater expansion of the piston crown area due to the extreme heat it operates in.

How do you check bearing clearance?

•Special feeler gauges or depth gauges (green) are used with a bridge gauges to take bearing clearances in larger bearings (Bridge gauge red and depth in green)

How do you find lower main bearing bearing clearances?

•by removal of the bearing shell. First the bearing bolts must be undone using hydraulic remover then upper bearing cap and upper bearing. The shaft is then lifted with jacks to roll out the bottom shell