It should be done when symptoms (engine miss, rough idle, puffing noise in induction or exhaust) point to major engine problems.

Measure compression pressures of all cylinders with a compression gauge.

Then compare them with each other and with the manufacturer’s specifications for a new engine. This provides an accurate indication of engine condition.

When gauge pressure is lower than normal, pressure is leaking out of the combustion chamber.

Low engine compression can be caused by the following conditions:

BLOWN HEAD GASKET (head gasket ruptured).

PHYSICAL ENGINE DAMAGE (hole in piston, broken valve, etc.).

BURNED VALVED SEAT (cylinder head seat damaged by combustion).

BURNED VALVE (valve face damaged by combustion heat).

WORN RINGS OR CYLINDERS (part wear that prevents a ring-to-cylinder seal).

VALVE TRAIN TROUBLES (valve adjusted with insufficient clearance.

This keeps the valve from fully closing. Also, broken valve spring, seal, or retainer).

JUMPED TIMING CHAIN OR BELT (loose or worn chain or belt has jumped over teeth, upsetting valve timing).

To perform a compression test on a gasoline engine, use the following procedures:

Remove all spark plugs so the engine can rotate easily.

Note

Some manufacturers warn against performing a wet compression test on diesel engines. If too much oil is squirted into the cylinder, hydraulic lock and part damage may result, because oil does not compress in the small cylinder volume.

Compression readings for a gasoline engine should 3-46 run around 125 to 175 psi. The compression should not vary over 15 to 20 psi from the highest to the lowest cylinder. Readings must be within 10 to 15 percent of each other. Diesel engine compression readings average approximately 275 to 400 psi, depending on the design and compression ratio. Compression levels must not vary more than about 10 to 15 percent (30 to 50 psi). Look for cylinder variation during an engine compression check. If some cylinders have normal pressure readings and one or two have low readings, engine performance is reduced. If two adjacent cylinders read low, it might point to a blown head gasket between the two cylinders. If the compression pressure of a cylinder is low for the first few piston strokes and then increases to near normal, a sticking valve is indicated. Indications of valve troubles by compression test may be confirmed by taking vacuum gauge readings.

Here i have included illustrations of some common problems.

Because many of the new alternators are capable of charging at rates in excess of 110 Amps, the battery should be fully charged before use to avoid overheating the alternator by trying to use it as a battery charger.

Alternators are NOT battery chargers, they are battery maintainers as well as supplying current for vehicle amenities. Symptoms of this type of damage are a burnt stator.

In many newer vehicles, the alternator is located in an area that allows very little ventilation. The area around the rectifier on the back of the alternator plugs up with dirt and fibers, causing the unit to overheat.

Rear alternator bearing failure be caused by over tightening the belt or a seized belt tensioner. The bearing is retained in the alternator by either an aluminum ring or a plastic retainer, which under pressure, will collapse.

Drive belt slippage cause overheating and bearing damage. Thread damage on the rotor of the alternator is caused by improper pulley installation methods.

Cracked terminal insulators are caused by over tightening the terminal nuts. Improper changing of the alternator clock position may result in broken brushes and brush holders.

Drive Belt Tensioner too Tight Bearing Damage

Problem:

Picture #1 shows the drive plate on this alternator which has been scored by the fan.

This is caused by the belt tensioner not operating properly. The tensioner could be tight or possibly seized, which puts extreme tension on the drive end bearing, causing premature bearing failure.

This can also cause the rear bearing to fail. ( Refer to picture #2 )

Solution:

It is extremely important that the installer check the operation of the belt tensioner before installing any alternator. If it does not work properly, REPLACE IT.

Drive Belt Slippage

Problem:

These pictures show fan belt material on the front of the drive end plates of the alternators. This is caused by fan belt slippage.

Slippage of the belt can be caused by a loose or glazed belt, worn or misaligned pulley. Often this can be detected by a shiny or discolored pulley (Blue) or this black belt material. Pulleys can be misaligned with the other pulleys on the engine when the installer changes them from one alternator to another. The proper spacers must be used or removed as required.

Solution:

Often fan belts that appear to be tight may not start to slip until alternator is under full load. It is extremely important to inspect the old alternator and pulley before replacing them. If the belt is worn, glazed or cracked, REPLACE IT.

Make sure the belt tension is correct. Applications without automatic belt tensioners must be adjusted manually. Applications with automatic belt tensioners must be inspected to see if they operate correctly, if not, REPLACE THEM.

Rotor Threads Damaged

Problem:

The enlosed picture shows that the rotor threads on the alternator shaft have been damaged (Stipped).

This can be caused when replacing the pulley and starting the nut on the thread with an air impact, or using a hammer when removing the pulley.

Solution:

Start the pulley nut by hand initially to avoid possible cross threading of the shaft. Then tighten to spec with air impact.

Do not use a hammer directly on the shaft when removing the pulley.

Cracked Terminal Insulator

Problem:

Cracked battery insulator on the alternator caused by over tightening. (Often caused by air impact)

Solution:

It is extremely important that these connections are tightened with a wrench, by hand, and not an impact. The installer must use caution when manually tightening these nuts, not to give that last reef on the wrench.

Fan Belt Problems

 On many occasions, soon after installing a new fan belt, the vehicle throws the belt off or shreds the outer edges. Here are a few of the causes of this type of problem.

On V-belt systems, worn pulleys, improper pulley alignment, or damaged pulleys are usually the cause of frayed or broken belts. V-pulleys require the pulley to have smooth, machined surfaces to ensure good belt to pulley contact that will prevent belt slippage.

Improper alignment will cause belts to climb and jump off the pulleys. Pulleys can be damaged by rocks or improper installation, causing knife edges to be formed, which will cut the sides of a fan belt when passing over this damaged area.

Serpentine belts systems have developed a whole new set of problems for the technician. Idler pulley or alternator bearing failure is a major cause of new fan belts being destroyed soon after installation. Usually the belt has burnt areas and the belt grooves have a sooty material in them.

When the sides of a serpentine belt become frayed, or lose a groove or two of belt material, the cause is probably a worn idler pulley. Flat idler and tensioner pulleys wear in the center, resulting in the sides of the pulley become raised. It is this raised portion of the pulley that causes damage to the sides of the belt.

Is the battery bad? Or is it simply discharged? To be sure, we need to measure the Specific Gravity of the electrolyte in each of its six cells. This test tells us the battery’s State of Charge.

As a battery discharges, the electrolyte contains more and more water and less acid. Since water is lighter than acid, the weight of electrolyte decreases as the battery discharges.

As the battery charges, the acid content of the electrolyte increases. Electrolyte in a charged battery weighs more by volume than electrolyte in a discharged battery.

We can use a hydrometer to test Specific Gravity and State of Charge in batteries with removable caps. Here’s how:

• Remove the battery caps. Check the electrolyte level. Make sure all cells are covered but not overfilled.
• Insert the hydrometer into each cell and draw electrolyte into the glass cylinder with the squeeze ball. Draw just enough acid into the cylinder to make the float rise. Hold the hydrometer vertical as each sample is drawn. Note the exact level at which the fluid level intersects the measurement scale on the float and record it.
• Repeat the test at each of the remaining cells. Record the reading for each cell. Compare readings to the chart on this page to determine state of charge.
• If the battery is below 75 percent state of charge, recharge it before load testing.

Temperature Correction

• If the temperature of the electrolyte is below 80 degrees F, subtract .004 (4 points) from the actual reading for each 10 degree change.
• Add 4 points for each 10 degree change above 80 degrees F.

For example, if the actual specific gravity reading is 1.265, but the electrolyte temperature is only 30 degrees F, then the true, corrected specific gravity is 1.245 (1.265-.020 = 1.245).

Why? Because the higher 1.265 specific gravity reading at 30 degrees F is the result of the increased density of colder electrolyte, not because the sample contains a higher concentration of acid.

Battery State of Charge – Refractometers

Refractometers are precision instruments that also measure the specific gravity of battery acid. (They can also measure antifreeze freeze protection for both ethylene glycol and propylene glycol antifreeze.)

Refractometer use is simple:

• Lift the clear sample window cover and place a drop of battery acid from one cell on the sample window.
• Close the sample window cover.
• Look through the eyepiece as you would look through a telescope.
• The point at which the light and dark areas of the measurement screen intersect the scale indicates the specific gravity of the sample.
• Record the reading and wipe the sample window clean before testing the next cell. Repeat the test for each of the remaining cells.

What Do Low Specific Gravity Readings Indicate?

Low specific gravity readings in all six cells tell us that the electrolyte in the cells is more water than acid, an indication that the battery is at a low state of charge. If the readings are uniformly low, however, there’s a reasonable chance that the battery may be all right once it is recharged.

Here are a few rules of thumb for interpreting specific gravity readings:

• The maximum allowable difference between the highest and lowest specific gravity reading is 50 points, whether you measure it with a hydrometer or refractometer. If the range between high and low readings is greater than 50 points, replace the battery.
• Abnormally high specific gravity readings (greater than 1.270) may indicate excess acid, possibly caused by someone adding acid, instead of water, to the battery.
• Specific gravity tests won’t identify a battery with an open or shorted cell.

Testing State of Charge in Sealed Batteries

The Open Circuit Voltage Test

If the battery has a sealed top, you cannot perform a specific gravity test to determine the battery state of charge since there is no way to take samples of the electrolyte.

To determine battery state of charge in sealed-top batteries, you must perform an Open Circuit Voltage test across the battery posts using an accurate digital voltmeter; analog voltmeters are not accurate enough for this test. Open Circuit Voltage (OCV) refers to voltage measured across the battery posts with no electrical loads turned on.

Adjust your digital multimeter to the 20 or 40 Volt SC scale and place the meter leads across the battery posts.

Take the voltage reading and compare it to the chart to the right. The chart combines specific gravity and OCV test standards.

There is a direct relationship between specific gravity and open-circuit voltage measured across the battery posts. Batteries below 75% of full charge must be recharged before performing a load test.

What State of Charge Can Tell Us

State of Charge tells us if the battery is sufficiently charged to undergo load testing. It does not tell us if the battery can deliver both voltage and current at the same time. That’s what the load test is for. Once it is determined that the battery state of charge is 75% or greater, the load test measures the battery’s ability to provide POWER. Power is measured as wattage, or volts multiplied by amps.

As batteries age and deteriorate, call material degrades or falls off and plates become less powerful. A battery that passes the specific gravity or open-circuit voltage tests may still have a hard time maintaining its voltage when electrical loads consume large amounts of current.

This is very important, so we will repeat it: Batteries must provide power.They must provide enough electrical current to operate all vehicle loads and still maintain the correct voltage.

An engine should be properly diagnosed before it is disassembled for two reasons. First, to determine that a repair is really necessary. And, secondly to diagnosis the exact location of the problem while the engine is still intact. Normally, main bearing inspection requires removal of the Oil Pan(Sump).

As shown below, bearings can fail for a variety of reasons. Oil starvation and dirt are the major reasons for bearing failure. Problems in other engine components, such as bent or twisted crankshafts or connecting rods, or out-of-shape journals, can also cause bearings to wear irregularly.

Inspect your bearings for these conditions.

Common forms of bearing distress.

A loose crankshaft main bearing produces a dull, steady knock, while a loose crankshaft thrust bearing produces a heavy thump at irregular intervals. The thrust bearing noise might only be audible on very hard acceleration. Both of these bearing noises are usually caused by worn bearings or crankshaft journals. To correct the problem, replace the bearings or crankshaft.

Main Bearing Service

Out-of-Round Journal Wear

When the engine is first turned over after the engine has not been run for a period of time, here is little or no lubrication between the crank and the lower main bearings. The result is that he lower main bearing wears excessively and the main journals wear out-of-round. When the main bearing that is farthest from the oil pump shows more wear than the other main bearings, a dry start condition is indicated. This means that the engine was probably revved before oil had filled the system. This problem occurs most often in cold weather.

Sometimes, all the lower main bearings will be worn except for the front bearing. This bearing usually wears less on the bottom because of the upward tension of the fan belt. Excessive belt tension can cause wear on the upper front main bearing. Connecting rod journals also wear out-of-round, wearing on their top sides because of excessive loads during the power stroke. Crankshaft main bearing journals wear out-of-round. Excessive loads cause the oil film to break down, resulting in wear. Excess loads can be caused by lugging the engine or by abnormal combustion.

NOTE

Lugging occurs when the load on the engine is greater than the rpm needed to develop enough horsepower to pull the load.

Measure the rod journal in a horizontal and vertical direction to check for out-of-round wear. Crank journals are miked (measured with a micrometer) at 90° angles to check for out-of-round wear, which should be less than 0.0005″.

Tapered Wear

Rod journals sometimes suffer taper wear due to misalignment of the connecting rod.

The presence of uneven rod bearing wear, and sometimes piston skirt wear usually indicates taper. Connecting rods should be checked for misalignment whenever uneven wear is found.

Thrust Bearing Wear

The thrust bearing surface that faces the rear of the engine sometimes shows excessive wear.

One side of this thrust bearing is burned.

Most thrust bearings have concaved reliefs cut into them to provide lubrication. Under normal conditions, the thrust surface is only under load when the clutch pedal is depressed or if the automatic transmission torque converter is under a load. Thrust bearing wear and failure occurs when the load is continuous, such as when there.

To measure the bearings for wear, taper and out-of-roundness:

• Using a service manual, look up the specifications for standard crankshaft size and tolerances for normal wear.
• Check the crankshaft and use proper procedures to clean it before beginning the measurement process.

Using the proper size outside micrometer, check the number 1 main bearing journal twice at each end of the journal, once horizontal to the crankshaft and once vertical.

Measuring the connecting rod journal with a micrometer.

• If these measurements are different than the vehicle’s specifications, the crankshaft main bearing journal is out-of-round or tapered and the crankshaft must be machined before it is installed in the engine.
• If any of the main bearing journals are out of specification, all main bearing journals should be ground to the next undersize. This ensures that the journals are on the same centerline. Another alternative is to build up the crankshaft journal using special welding techniques, then grinding the journal to its original size.

NOTE

If the main bearing or connecting rod journals have pits, yet measure within specifications, polish the worst journal. After the journal is clean of pits, re-measure it. If it is still within specifications, the crankshaft will not require grinding.

Check for out-of-roundness and taper.

• Repeat these steps for each of the remaining main bearing journals.
• Measure the number 1 connecting rod journal twice at each end of the journal, once horizontal to the crankshaft and once vertical.
• If these measurements are different, the crankshaft connecting rod journal is out-of-round or tapered, and the crankshaft must be machined before it is reinstalled in the engine.
• Repeat these steps for each of the remaining connecting rod journals.

NOTE

Not all do-it-yourselfers will have the tools necessary to perform these jobs. They can be completed in a machine shop.

Journal Grinding

The manufacturer often applies a hardening treatment to the journals to protect them from wear. However, even with hardened surfaces, the bearing journals can become scored or scuffed due to improper lubrication, excessive heat, contamination, or improper installation. It may be possible to restore the journal surface by grinding them to a standard undersize. Grinding of the crankshaft journals is done to correct any of the following conditions:

• Out-of-round
• Taper
• Improper oil clearances
• Scratches, scoring, or nicks
• Damaged thread surfaces

Before grinding the journals, attempt to determine the hardness of the journal. Hardness values are expressed using the Rockwell C (Rc) scale. Electronic hardness gauges are available to determine the journal’s Rc value. Nitral acid etching is another method of determining the hardness of the journals. Generally, crankshafts with fillet-hardened journals should have values above 36 Rc. Crankshafts without fillet-hardened journals should have values above 30 Rc.

Crankshaft journals hardened using Tuff riding or Melonite treatments (both are forms of salt bath nitriding) cannot be machined. These processes are too thin, and machining the journals will remove all hardening. To determine if these hardening processes were used on the crankshaft, file a small portion of the counterweight using a medium-fine mill file. If metal can be removed under light filing pressures, the crankshaft has not been treated using these methods.

As with most machining operations, when grinding the crankshaft, do not remove any more metal than necessary. Generally, journals are ground to under sizes of 0.010, 0.020, or 0.30 inch. not all rod journals need to be the same undersize. It may be necessary to machine only one rod journal to an undersized while the others remain standard. However, it is recommended that the main bearing journals be machined to the same undersize to be sure the centerline is on the same plane.

Whenever the crankshaft journals are undersize, it is a good practice to stamp the size of the rod and main journals on the face of the first counterweight. If the main bearing journals are ground to different under sizes than the rod journals, list the main journals first. For example, if the main journals are undersized 0.020 inch and the rod journals are undersized 0.030 inch, the marking will be made as 0.20-0.30. This will alert the next technician rebuilding the engine (or using the crankshaft) that the crankshaft has been undersized.

Polishing

The machining of the journals and seal surfaces of the crankshaft leaves these surfaces too rough to run bearings or seals on. After the journals are ground, they must be polished to remove this roughness. Generally, the crankshaft is rotated in the opposite direction during the polishing procedures than it was run during the grinding procedure.

Polishing is not a final sizing operation. The maximum amount removed by this procedure should not exceed 0.0002 in. (0.005 mm). The polishing procedure can be done while the crankshaft is attached to the grinding machine using a portable polisher. In addition, a special crankshaft polishing machine can be used or the journals can be polished by hand lapping.

Both types of machines work similarly, using a belt sander-type setup to polish the journals. The crankshaft is rotated and the belt is run back and forth across the journal. Continue to polish the journal until it is smooth and shiny. A surface of 32 in. on the bearing journals and 15 uin. on the bearing journals and 15 uin. On the sealing surface is usually desired. Hand lapping is done using a piece of emery cloth wrapped around the journal. Start with a medium grit cloth and finish with a 320-grit cloth. A finish of 15 uin. is usually obtained by hand lapping.

After the journals and sealing diameters are polished, the blend radius of the oil holes must be deburred and rounded. Polishing the oil holes prevents early bearing failure by removing the sharp corners. This operation can be done using a die grinder or jeweler’s rouge.

When the polishing procedure is completed, the crankshaft must be thoroughly cleaned any residue from the grinding and polishing procedures left on the crankshaft or in the oil passages will quickly destroy the journals.

Building Up Crankshaft Journals

Another available option for reconditioning the crankshaft journals is to build up the journal area, then machine it to standard size. This process is used when the journal is worn or damaged so excessively that no undersized bearing can be used to correct oil clearance. There are two common methods used to build up the journals: chromium plating and submerged arc welding.

The process of chromium plating electrically plates hard chromium onto the bearing journal surfaces. After the plating is built up to the required amount, the journals are ground to restore the original size.

A crankshaft welder uses a wire feed-type welding system using flux to displace oxygen. Before the beads are welded to the journal, the journals are ground to remove impurities in the surface area. Carbon plugs are tapped into the oil passages to prevent them from being filled.

The crankshaft is attached to the welding machine between two chunks and is rotated while the weld bead is spiraled around the journal. The process continues until the weld bead has worked across the entire width of the journal. After the welding process is completed, the slag is removed and the journal is ground. Welding to build up the journals provides a very hard surface.

Main Bearing Replace

Main bearings are replaced with the crankshaft in the engine using a tool installed in the oil feed hole in the journal. The bearings must be rolled out on the side opposite the bearing locating lug, or tang.

Main bearings can be rolled out and new bearings rolled back in. If the special tools are not available, you can make one out of a cotter pin.

When selecting new main bearings, make sure they match the crankshaft journal diameters and main bearing bores. If the crankshaft has been ground undersize, the main bearings will also have to be undersize. Similarly, if the housing bores have been machined oversize by align boring or align honing, the bearings must take up this space. Bearing size is usually marked on the bearing box and on the back of the bearing.

When the bearings are ready to be installed in the main bearing bores, make sure the bore is clean and dry before installing the bearing halves into place. Use a clean, lint-free cloth to wipe the bearing back and bore surface.

Put the new main bearing inserts into each of the main bearing caps and into the bearing bores in the cylinder block housings.

Place the bearing inserts into the bore; make sure the locating lugs fit into their recess.

Make sure all holes align. The backs of the main bearing inserts should never be oiled or greased. Place the crankshaft in the block on the main bearing inserts and arrange the main bearing caps in the correct order and direction over the crankshaft. Follow the factory markings or use those made during disassembly.

The next step is to measure the oil clearance between the crankshaft and the main bearing. Proper lubrication and cooling of the bearing depend on correct crankshaft oil clearances. Scored bearings, worn crankshaft, excessive cylinder wear, stuck piston rings, and worn pistons can result from too small an oil clearance. If the oil clearance is too great, the crankshaft might pound up and down, overheat, and weld itself to the insert bearings.

Plastigage is fine, plastic string used to measure the oil clearance between the bearing and the crankshaft. One side of the plastigage’s package has stripes for inch measurements, the other side has stripes for metric measurements. The string can be purchased to measure different clearance ranges. Usually, only the smallest clearance range is necessary for reassembly work.

Tighten the Main Caps

For a five-main bearing block, the torque sequence is 1-4-3-2-5.

NOTE

As each main cap is torqued down, check to see that the crank continues to turn easily.

After the rear cap is removed, check the rear seal drag. Some manufacturers give a torque specification for the amount of effort required to turn the crank with the damper bolt in an assembled engine.

Align the Thrust Bearing Halves

Torque all bearing caps except the thrust main. Its halves should be aligned before torquing.

Misaligned thrust halves could eliminate end play. This is done by prying on the crankshaft while the thrust main is still loose.

Checking crankshaft end play: With a feeler gauge & With a dial indicator.

Bearing Types

Bearings are used to carry the critical loads created by crankshaft movement. They are a major wear item in the engine and require close inspection. Main bearings support the crankshaft journals. Connecting rod bearings are installed between the crankshaft and connecting rods.

Modern crankshaft bearings are known as insert bearings. There are two basic designs of insert bearings.

Full-round and split insert bearings.

A full round (one-piece) bearing is used in bores that allow the shaft’s journals to be inserted into the bearing, such as a camshaft. A split (two halves) bearing is used where the bearing must be assembled around the journal with the bearing housing being of two parts also, including a cap that holds the assembly together. Crankshaft bearings are typically the split type.

Many crankshafts are fitted with a main bearing that has flanged sides. This type bearing is typically called a thrust bearing and is used to control any horizontal movement or endplay of the shaft. The flange bearing is used in the thrust position of the block. Most thrust main bearings are doubled flanged.

Some late-model engines do not use separate main bearing caps; instead they are fitted with a lower engine block assembly.

Bearing Spread

Most main and connecting rod bearings are manufactured with spread. Bearing spread means that the distance across the outside parting edges of the bearing insert is slightly greater than the diameter of the housing bore. To position a bearing half that has spread, it must be snapped into place by a light forcing action.

Spread requires a bearing to be lightly snapped into place.

This assures positive positioning against the inside of the bore and helps to keep the bearings in place during assembly.

Bearing Crush

Each half of a split bearing is made so that it is slightly greater than an exact half. This can be seen quite easily when a half is snapped into place in its housing. The parting faces extend a little beyond the seat.

Crush assures good contact between the bearing and the housing.

This extension is called crush. When the two bearing halves are assembled and the housing cap tightened, the crush sets up a radial pressure on the bearing halves so they are forced tightly into the housing bore.

Bearing Locating Devices

Engine bearings must be provided with some means to keep them from rotating or shifting sideways in their housings. Many different methods have been used by manufacturers to keep the bearings in place. The most common way is the use of a locating lug. As shown below, this consists of a protrusion at the parting face of the bearing. The lug fits into a slot in the bearing’s bore.

The locating lug fits into the slot in the housing.

Oil Grooves

Providing an adequate oil supply to all parts of the bearing surface, particularly in the load area, is an absolute necessity. In many cases, this is accomplished by the oil flow through the bearing oil clearance. In other cases, however, engine operating conditions are such that this oil distribution method is inadequate. When this occurs, some type of oil groove must be added to the bearing. Some oil grooves are used to assure an adequate supply of oil to adjacent engine parts by means of oil throw-off.

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ENGINE CLICKING NOISES

A clicking or tapping noise that gets louder when you rev the engine is probably “tappet” or upper valvetrain noise caused by one of several things: low oil pressure, excessive valve lash, or worn or damaged parts.

First, check the engine dipstick to see if the oil level is low. If low, add oil to bring it back up to the full mark.

Is the engine still noisy?

Check your oil pressure. A low gauge reading (or oil warning light) would indicate a serious internal engine problem that is preventing normal oil pressure from reaching the upper valvetrain components. The cause might be a worn or damaged Oil pump, a clogged oil pump pickup screen or a plugged up oil filter.

Using too thick a viscosity of motor oil during cold weather can also slow down the flow of oil to the upper valvetrain, causing noise and wear.

COLLAPSED LIFTER NOISE

Worn, leaky or dirty lifters can also cause valvetrain noise. If oil delivery is restricted to the lifters (plugged oil galley or low oil pressure), the lifters won’t “pump up” to take up the normal slack in the valvetrain. A “collapsed” lifter will then allow excessive valve lash and noise.

VALVE LASH NOISE

If you can rule out lubrication-related problems as a cause, the next step would be to remove the valve cover(s) and check valve lash.

On older import engines, mechanical lifters require periodic valve lash adjustments (typically every 30,000 miles). Too much space between the tips of the rocker arms and valve stems can make the valvetrain noisy — and possibly cause accelerated wear of both parts.

To measure (and adjust) valve lash, you need a feeler gauge. The gauge is slid between the tip of the valve stem and rocker arm (or the cam follower or the cam itself on overhead cam engines) when the piston is at top dead center (valve fully closed). Refer to a manual for the specified lash and adjustment procedure. Also, note whether the lash spec is for a hot or cold engine (this makes a big difference!).

On engines with hydraulic lifters, oil pressure pumps up the lifters when the engine is running to maintain zero lash in the valvetrain. This results in quiet operation. So if the rocker arms are clattering, it tells you something is amiss (bad lifter or worn or damaged parts) or the rocker arms need adjusting.

DAMAGED ENGINE PARTS NOISE

Inspect the valvetrain components. Excessive wear on the ends of the rocker arms, cam followers (overhead cam engines) and/or valve stems can open up the valve lash and cause noise. So too can a bent pushrod or a broken valve spring.

RAPPING OR DEEP KNOCKING ENGINE SOUND

Usually bad news. A deep rapping noise from the engine is usually “rod knock,” a condition brought on by extreme bearing wear or damage. If the rod bearings are worn or loose enough to make a dull, hammering noise, you’re driving on borrowed time. Sooner or later one of the bearings will fail, and when it does one of two things will happen: the bearing will seize and lock up the engine, or it will attempt to seize and break a rod. Either way your engine will suffer major damage and have to be rebuilt or replaced.

Bearing noise is not unusual in high mileage engines as well as those that have been neglected and have not had the oil and filter changed regularly. It can also be caused by low oil pressure, using too light a viscosity oil, oil breakdown, dirty oil or dirt in the crankcase, excessive blowby from worn rings and/or cylinders (gasoline dilutes and thins the oil), incorrect engine assembly (bearings too loose), loose or broken connecting rod bolts, or abusive driving.

Bearing wear can be checked by dropping the oil pan and inspecting the rod and main bearings. If the bearings are badly worn, damaged or loose, replacing the bearings may buy you some time. But if the bearings are badly worn or damaged, the crankshaft will probably have to be resurfaced — which means a complete engine overhaul or replacing the engine is the vehicle is worth the expense.

ENGINE PINGS OR KNOCKS WHEN ACCELERATING

The cause here may be Spark Knock(Detonation) caused by an inoperative EGR valve, overadvanced ignition timing, engine overheating, carbon buildup in the combustion chambers, or low octane fuel.

INSPECTION RECORD

JOB NO………………..

DATE………………….

1) Chassis No……………                          2) Engine No………………………………..

3) Vehicle Reg. No…………….                 4) Kms………………………………………

5) Nature of failure………………………………………………………………………..

6) Kms covered after last rebuild…………………………………………………………

01. CYLINDER BLOCK

Block No…………………

02. CRANK SHAFT

Crank shaft no……………………….

03. CONNECTING ROD

04. CYLINDER HEAD

05. ROCKER LEVER/PEDASTALS/TAPPETS PUSH ROD

06. CAMSHAFT

07. VIBRATION DAMPER

08. PISTON PIN

09. OIL FILTER HEAD

10. OIL COOLER

11. OIL PUMP

12. WATER PUMP

13. FAN HUB

14. BELT TENSIONER

15. THERMOSTAT

16. TURBO CHARGER

17. EXHAUST MANIFOLD