Ch6. Crankshafts

Built up crankshaft

(Forged in separate sections and flanged together) are used in a few large engines.

Full round bearings

(One piece) are used when it is possible to slide the journal into place in the bearing.

Seizure resistance

(Surface action) the ability to withstand metal to metal contact without being destroyed. It is difficult to avoid some metal to metal contact during starting or when the oil film becomes thin during operation

Split bearings

(Two halves) are used when the bearing must be assembled around the journal

2. What are 2 methods normally used to recondition the main and connecting rod journals?

- grinding the journals to remove material from the surface - rebuilding the journals be adding material to the surface

3. List at least 3 advantages of insert type bearings

- most inserts can be adjusted - bearing spread on the thin walled inserts, such as connecting rod bearings, can be adjusted by hand - most often used in high speed Diesel engines - two types of insert bearings- full round bearings and split bearings

4. Name the 2 types of insert bearings used in modern Diesel engines

- precision insert bearings which are manufactured to close tolerances so that no further sizing is required at time of engine assembly - resizable insert bearings are manufactured with an extra thick lining of bearing material on the inside diameter. This extra material permits the bearing to be machined to the desired size at the time of assembly

1. Briefly define the following crankshaft parts: journal, throw, and counterweight

- the main bearing journals serve as the crankshafts center of rotation and primary means of support - each crankshaft throw consists of three parts- two webs and a connecting rod journal. The throws provide points of attachment for the connecting links between main journals - counterweights balance the off center weight of the individual throws, keeping the centrifugal force generated by each rotating crank in equilibrium

3. Which of the following is a typical out-of-round specification for main and connecting rod journals?

.001" (.025mm)

Harmonic balancer

A device that is mounted on one end of a crankshaft. Used to reduce torsional vibration.

Oil seal

A device used to prevent oil leakage past certain areas, such as around a rotating shaft

Crankshaft gear

A gear that is pressed on the crankshaft. Used to drive a chain or belt which drives the camshaft gear.

Flywheel

A large heavy wheel that forms the base for the starter ring gear and provides a mounting surface for the torque converter or clutch assembly.

Plastigage

A measuring tool that is compressed between two tightly fitting surfaces, such as bearings, to measure clearance

Aluminum

A metal known for its lightweight and good heat dissipation characteristics. It is often alloyed with other metals

Vibration damper

A round metal or rubber weight attached to a crankshaft or other part to minimize vibration.

Bimental bearing

A simple bearing uses two laters. One layer is a steel backing and the other is a liner of bearing material.

Babbitt

A tin or lead based material that can be divided into two categories- conventional babbitt and micro(thin) babbitt.

Flanged thrust bearing

A variation of the common split bearing found in most Diesel engines. Provides the same support as the split bearing but it also controls and horizontal crankshaft movement

8. Which of the following jobs may be performed by the flywheel?

All of the above. - absorbs and gives up energy to keep shaft rotation uniform - helps bring the engine up to speed when it is being cranked - provides a drive from the starting motor via the ring gear, and serves as a facing for the engine clutch

Precision insert bearings

Are manufactured to close tolerances so that no further sizing is required at time of engine assembly

2. Technician A says that a magnetic particle test is the best method of detecting small cracks in a crankshaft. Technician B says that a fluorescent magnetic particle test is a better method. Who is right?

B only

9. Technician A says that you should use a jaw pulled to remove a two piece vibration damper. Technician B says that you should use the tools recommended by the service manual to remove a two piece vibration damper. Who is right?

B only

Counterweights

Balance the off center eight of the individual throws, keeping the centrifugal force generated by each rotating crank in equilibrium

Precision balancing equipment

Balancing crankshafts and other rotating components is a precision operation. These components can be balanced to a fraction of a gram with precision balancing equipment. Crankshaft balance is as important as straightness. This is normally done by an electronic crankshaft balancing machine

5. Babbitt, sintered copper lead, cast copper lead, and aluminum are all materials used in the construction of ________?

Bearings

Sinter copper lead

Bearings are made by a process known as sintering(heating without melting). During this process, lead and copper metal powders are fused to a steel strip.

Cast copper lead

Bearings are made by casting copper lead allot on a steel backing. It is available also with or without an overlay

10. An engine "throws" drive belts. This indicates _____?

Belt misalignment AND bent sheaves

1. Technician A says that a six cylinder in line engine will have six connecting rod journals. Technician B says that a V-8 Engine will have 4 connecting rod journals. Who is right?

Both A and B

7. Technician A says you should determine bearing clearance by using a micrometer to measure combined bearing thickness, bore diameter, and journal diameter, and then performing a series of simple calculations. Technician B says you should determine bearing oil clearance using plastigage. Who is right?

Both A and B

Fluorescent penetrant

Can be used on both ferrous and nonferrous materials. A highly fluorescent liquid penetrant is applied to the part. After the excess penetrant is removed from the surface, the part of dried. A developing powder, which helps to draw the penetrant out of the flaws by capillary action is applied to the part

Wear limits

Compare measurements with service manual specifications and establish wear limits to determine the underside to which the crankshaft can be reground

Dynamic balance

Condition when the centerline of a revolving object is in the same plane as the object itself

Bending fatigue

Crankshaft failures can occur from bending fatigue. The crankshaft is supports between each of the cylinders by a main bearing. An abnormal bending stress in the crankshaft may be the result of many problems

6. Many ______ can be serviced without removing the front cover, trunnion, or flywheel housing

Crankshaft oil seals

Crocus cloth

Emery cloth. Crocus cloth is an abrasive sheet similar to sand paper or emery cloth but covered with a layer of very fine loose iron oxide particles rather than with bound grains of abrasive. It is intended for final metal and gemstone finishing and is available in various grades

6. What type of bearings and other components are used to withstand the fore-and-aft movement of the crankshaft in the engine block?

Flanged thrust bearings AND separate thrust washers

9. The __________ maintain the alignment of the flywheel housing on the engine

Flywheel dowels

Bearing crush

Helps create a tight fit between the insert and the bore

Resizable insert bearings

Manufactured with an extra thick lining of bearing material on the inside diameter. This extra material permits the bearing to be machines to the desired size at the time of assembly

Torsional failures

May also occur at the crankshaft timing gear key slot. Torsional stresses may produce a fracture in either the connecting rod journal or the rear of the crank cheek

Static balance

Obtained when the weight is distributed equally in all directions from the center of the crankshaft while it is at rest

Throw

Offset portion of the crankshaft designed to accept a connecting rod

Connecting rod journals

Often called crank pins. The throws provide points of attachment for the connecting links between main journals

Front oil seal

Prevents oil leakage between the crankshaft and front cover

Embeddability

Refers to a bearings ability to let small dirt and metal particles embed themselves to avoid scratching the part

7. A cracked crankshaft timing gear must be ________

Replaced

Oil passage

Runs from a main bearing journal to a connecting rod journal. The oil passages are in pairs that crisscross each other in such a way that two oil holes are on opposite sides of the journal

8. To keep bolt heads from marring the flywheel surface, a _______ is sometimes used

Scuff plate

Main bearing journals

Serve as the crankshafts center of rotation and primary means of support.

Thrust surfaces

Should be checked for roughness and scoring. Also check the thrust width with an inside micrometer. If the surfaces are damaged or the widths are not within specifications, the crankshaft should be reground

Fluorescent magnetic particle test

Similar to the magnetic particle method but is more sensitive since it employs magnetic particles that are fluorescent and glow under a black light

Thrust washer

Some applications where separate thrust members, called thrust washers, are used in pace of thrust bearings, particularly in heavy duty Diesel engines

Trimental bearing

Some designs use a third layer, which is an overlay in the bearing material liner. The overlay is bearing material also but is different than the material used to form the liner. This type of bearing is known as trimental bearing.

Webs

Sometimes called cheeks or arms. Each crankshaft throw has two webs

Conformability

The ability of a bearing insert to creep or flow slightly so that the shaft and bearing will conform to each other

Corrosion resistance

The ability of the bearing material to resist chemical corrosion

Temperature strength

The bearing materials ability to carry its load at high operating temperatures

Magnetic particle test

The crankshaft is magnetized and then covered with a fine magnetic powder or solution. Any flaws, such as cracks, will cause the magnetic particles in the powder or solution to gather, effectively marking the cracks. The crankshaft must be demagnetized after the test

Bearing spread

The distance between the outside parting edges of the bearings is wider than the diameter of the bore in which they are to be used.

Crankshaft

The main shaft which supports the connecting rods and turns piston reciprocation into motion.

4. Which type of Diesel engine design is more prone to bearing wear on the lower half of the main bearings and lower half of the piston pin bearings?

Two stroke engine

10. A ________ or ______ is used to dampen the torsional vibration of the crankshaft

Vibration damper or harmonic balancer

5. What is the most common cause of bearing distress a. Dirt b. Lack of lubrication c. Misassembly d. Misalignment

a - dirt

torsional vibration

occurs when an object twists around its axis. The forces in a Diesel engine are produced and transmitted to the crankshaft in a pulsating manner. These pulses create torsional vibrations that are capable of severely damaging an engine if they are not diminished or "damped" but opposing forces