Engine Vacuum Test

Throttle plate opening controls the amount of air that can enter the engine. Movement of the accelerator pedal opens or closes the throttle plate, changing engine vacuum. For a stock engine, vacuum should range from 16 to 22 in. Hg at idle, and the needle should be steady (Figure 3.24). An engine has higher vacuum when it is operating under light load. Vacuum drops to zero under WOT.
• At idle, with the throttle plate nearly closed (Figure 3.25a), engine vacuum will be high.
• At medium throttle opening, when cruising (Figure 3.25b), engine vacuum will be in the neighborhood of 8 to 10 inches.
• At WOT (Figure 3.25c), engine vacuum is zero.

A leaking intake manifold gasket can cause an engine to idle rough, especially when cold, before oxygen sensor feedback begins. The oxygen sensor can compensate for small vacuum leaks to a certain extent. At speeds above idle, symptoms of a leaking

a

b
FIGURE 3.23 (a) A vacuum gauge reads pressure when the needle
moves clockwise and “vacuum” when the needle moves counterclockwise.
(b) Connect the vacuum gauge to an intake manifold vacuum source.

FIGURE 3.24 Normal engine vacuum

intake manifold diminish because the size of the leak is proportionally less as the engine breathes more air.

A leaking intake manifold gasket can result from sloppy cleanup of gasket surfaces during manifold installation, from failing to clean out bolt holes, or from bottoming out bolts that are too long. 

A car with an oxygen sensor feedback fuel system can run rough when cold but run fine after warm-up when the computer responds to the oxygen sensor signals by compensating with a richer

air-fuel mixture.

One vacuum test for a manifold gasket leak is to pinch off the two PCV valve hoses—the one to the intake manifold and the breather hose to the air cleaner—then run the engine. If there is vacuum at the oil filler opening, an intake manifold-tocrankcase vacuum leak is indicated.

To test for weak piston rings (Figure 3.26):

• Raise the engine speed to about 2000 rpm.

• Snap the throttle closed and watch for an

increase of 2 to 6 inches of vacuum above normal.

• Worn rings will not increase vacuum sufficiently during deceleration. Generally, the higher the rise, the better the condition of the rings.

FIGURE 3.26 Vacuum readings for weak piston rings.

Sticky valves are indicated when the needle drops quickly or drifts. This could be because valves are hanging up in their guides rather than closing freely (Figure 3.27). The movement will have no apparent rhythm. Leaking valves (Figure 3.28) are indicated when the needle drops at regular intervals. A power balance test will pinpoint the low cylinder.

FIGURE 3.27 Vacuum reading for sticky valves

FIGURE 3.28 Vacuum reading for leaking valves.

FIGURE 3.29 Vacuum reading for bad valve springs

Bad Valve Springs. Sometimes valve springs that are too short or too weak have been installed by accident. Otherwise, valve springs weak enough to cause this problem are rare. To test for weak valve springs with a vacuum gauge (Figure 3.29):

• Raise engine rpm slowly to 2000.

• Look for rapid fluctuations of the needle as speed increases.

• An exhaust analyzer will have a good hydrocarbon (HC) reading at idle but bad under acceleration.

Restricted Exhaust. To test for a restricted exhaust (Figure 3.30):

• Raise the engine rpm quickly to 2000 to cause the vacuum reading to go momentarily low and

then release the throttle quickly. • Vacuum should return smoothly and quickly to higher than normal levels.

• A slow, hesitating return can indicate a breathing restriction.

When an engine with weak valve springs is accelerated, hydraulic lifters can overfill (pump up).

There is no noise, but the engine will run rough when it returns to idle.

According to one Auto Engine Rebuilders Association (AERA) bulletin, incorrect valve spring tension

can result in a rough idle that is only apparent on initial cold startup. OBD II engine computer systems

sometimes sense this misfire and cause the malfunction indicator lamp (MIL) on the dash to illuminate.

Restricted Exhaust. To test for a restricted exhaust (Figure 3.30):

FIGURE 3.30 Vacuum reading for restricted exhaust

• Raise the engine rpm quickly to 2000 to cause the vacuum reading to go momentarily low and then release the throttle quickly.

• Vacuum should return smoothly and quickly to higher than normal levels.

• A slow, hesitating return can indicate a breathing restriction.

Other Causes of Low Vacuum. Port fuel injected engines use O-rings to seal each individual fuel injector where it enters an intake port (Figure 3.31).

FIGURE 3.31 O-rings seal the fuel injectors where they enter the

intake ports

When an O-ring leaks, the resulting vacuum leak and lean air-fuel mixture in that cylinder cause a rough idle (Figure 3.32).

FIGURE 3.32 Fuel injection O-rings can become hard and brittle
with age, resulting in a rough idle, especially during open-loop operation
when the engine is first started and the computer is not receiving
feedback from the oxygen sensor

If an engine is equipped with an air pump for emission control, be sure that it does not have a 

When an engine with weak valve springs is accelerated, hydraulic lifters can overfill (pump up). There is no noise, but the engine will run rough when it returns to idle.

According to one Auto Engine Rebuilders Association (AERA) bulletin, incorrect valve spring tension

can result in a rough idle that is only apparent on initial cold startup. OBD II engine computer systems sometimes sense this misfire and cause the malfunction indicator lamp (MIL) on the dash to illuminate.

Cylinder Leakage Test (CLT)

The cylinder leakage test can accurately pinpoint causes of leakage. Regulated compressed air is introduced into the cylinder through its spark plug hole (Figure 3.22). The piston is positioned at top dead center (TDC) on the compression stroke, ensuring that both valves are completely closed.
• It is better to perform a cylinder leakage test when the engine is warm and the rings are sealed with oil. Otherwise, a small amount of movement at TDC can allow the piston ring to move off its ring land, allowing leakage
• An acceptable leakage reading on the tester’s gauge is usually less than 10% to 15%, although vehicles with up to 30% leakage might still be performing to the owner’s satisfaction. The owner might not notice the power difference until it is restored after an overhaul, because the loss in power has happened gradually.

If a cylinder shows high leakage, listen to locate the sound of the leaking air. The following lists cylinder leakage test results. Here are some possible locations for leaking air and the likely causes:
• Oil filler = leaking rings or piston
• Manifold intake = leaking intake valve
• Exhaust pipe = leaking exhaust valve

FIGURE 3.22 A cylinder leakage tester is connected to the cylinder

through a hose to the spark plug hole

• Bubbles in the radiator = blown head gasket, or a crack in the head or block, which allows the regulated air to enter the cooling system


The leakage tester offers three advantages over a compression test:
1. The test can be performed on an engine that is removed from a car (such as an engine purchased at a salvage yard).
2. The exact source of leakage can be pinpointed before engine disassembly.
3. A racing camshaft will not affect the results of the test. It would cause lower readings on the compression test, however, because engine vacuum is lower at cranking speeds with a racing cam.


SHOP TIP


If leakage is past the piston rings, the PCV valve could allow air to travel into the intake manifold where it can cause the technician to mistakenly suspect a leaking intake valve. To avoid this situation, remove the oil filler cap, or disconnect the vacuum line to the PCV valve or pinch it with pinch pliers.


NOTES
• If a high mileage engine tests OK on the power balance test and has compression within expectations but has excessive cylinder leakage test results, carbon deposits in the combustion chamber could account for the relatively good compression, although the engine will probably have excessive blowby and may lack power.
• When a cylinder bore has considerable taper wear on the top, the reading can be improved if the piston is moved slightly past TDC into a less worn area.

Electronic Cylinder Power Balance Testing

Vehicles produced since the mid-1990s have sophisticated on-board diagnostics called OBD II. Figure 3.21 shows a screen shot of a scan tool during an electronic power balance test. The scan tool disables fuel injectors rather than the ignition system. This eliminates the possibility of catalytic converter damage and oil dilution from raw fuel entering the crankcase during the test.

FIGURE 3.21 Electronic cylinder power balance. When an injector is

disabled, engine rpm should drop

 A cylinder that causes less drop than the others is not pulling its full load. Variations in rpm drop between cylinders should be less than 5%. A problem could be caused by the ignition system or fuel system, or the engine could have vacuum leaks or compression problems. Occasionally, rpm will rise as a cylinder is shorted out due to exhaust gas entering the intake manifold. This can be caused by an EGR valve that is open. (EGR should be closed at idle.) Like an air leak (also called a vacuum leak), EGR leaks cause a drop in manifold vacuum. But EGR leaks do not respond when you richen the mixture like air leaks do. The cylinder causing the rise in engine rpm is the one from which the exhaust gas for the EGR valve was picked up. Retest at cruise rpm and the problem will disappear.

The cylinder power balance test can also be done with the engine running at higher speeds than idle. Compare results at low and higher speed.


An engine with a burned valve will perform poorly at low engine rpm but would improve at higher rpm. A leaking valve does not have as significant an effect at higher speed as it does at low speed because the air coming into the engine and leaving it is moving too fast and has a much higher volume.

A restriction in the intake, like that caused by a worn cam lobe, with hydraulic adjustment will result in little change in engine operation at idle. The problem will become gradually more pronounced as speed is increased.

Compression Test Procedure

• Use caution when removing secondary (spark plug) wires. First, twist the rubber boots to loosen them from the spark plugs.

• Clean around all the spark plugs with compressed air. Then remove all spark plugs, so that the starter can crank the engine easily.
• Block the throttle in the wide-open position. This can be done with a throttle depressor

• Insert the compression gauge into a spark plug hole.
• Crank the engine through at least four compression strokes.
• Check and record each pressure reading.

The gauge will move four times, or with all the plugs removed you can hear each compression
stroke as the compression in the cylinder being tested slows the engine.

• Connect a remote starter between the S terminal on the starter solenoid and the ungrounded battery post.
• The compression test is done with the ignition switch in the “on” position to prevent damage to the electrical system on some vehicles. Disable the ignition system by pulling the battery-todistributor wire on cars with electronic ignition. Follow the manufacturer’s instructions.


Interpreting Compression Test Results. If all cylinders are performing equally and engine performance
is acceptable, the engine passes the test. When compression test specifications are available,
they are only an estimate. If specifications are not available, locate the compression ratio in the specification manual and use the following
formula:

Compression Ratio × Atmospheric Pressure +

Atmospheric Pressure + 5 (Volumetric Effi ciency)

For example, to figure out the approximate compression on an 8:1 engine at sea level (14.7 psi atmospheric
pressure):

8.0 × 14.7 + 14.7 + 5 = 137.3 psi

Variations in compression among cylinders should be no more than 20%. When two cylinders

next to each other have low compression, a blown head gasket is usually indicated. One or several cylinders with low compression and no apparent pattern of loss often indicates burned exhaust valves with rough idling as a symptom. At higher rpm, the rough running from the burned valve may
disappear.


Wet Compression Test. When cylinders show poor results, perform a wet compression test.
• Squirt about a tablespoon of oil into each low cylinder. The oil makes a seal around worn rings, boosting the compression reading.
• When cylinder readings are low but increase to normal during a wet test, a piston ring problem
is indicated.


Running Compression Test
The running compression test, or volumetric efficiency test, is used when the cause of a cylinder misfire
cannot be pinpointed or when an engine lacks power. First, perform a regular cranking compression
test and record all of the results. Then install all of the spark plugs except for one and install a compression
tester in that hole. Start the engine, and depress the release pin on the Schrader valve to allow the reading to stabilize.


Snap Compression Test. The next step is to snap the throttle wide open and let the engine return to idle. When it is first snapped, the throttle plate is wide open while the piston speed is relatively low. This will result in a higher reading. The compression gauge will hold this reading until the Schrader valve is manually released.
Record your snap compression test readings. Typical readings will be around 80% of cranking compression
readings. Lower snap readings mean that the intake system is restricted. Higher readings indicate an exhaust restriction. Problems in only one cylinder point to a worn cam lobe, broken valve spring, etc. Problems in all cylinders can be traced to a restriction in the air intake system or a plugged exhaust pipe or catalytic converter.

Testing for Compression Loss

For an engine to run, it must have three things:
• Sufficient compression
• Fuel (in a flammable ratio to air)
• Ignition (timed at the appropriate instant)
A quick way to check for uneven compression between cylinders is to disable the ignition system and crank the engine. An uneven cranking rhythm indicates unequal compression.


Compression Test
One of the most common and least expensive pieces of test equipment is the compression tester. A compression tester is simply a pressure gauge that is inserted into a spark plug hole. There are two styles of compression testers. One is held in place while cranking the engine (Figure 3.19a). It is handy on in-line engines because it is fast and easy. The other type is the screw-in tester. Spark plugs use one of two thread sizes. The tester

a

b
FIGURE 3.19 Compression testers. (a) This compression tester
can be used when there is easy access to the spark plug holes.
(b) A screw-in compression tester with adapters. The adapter shown
on top is for larger-diameter spark plug threads. The two adapters
beneath it are for different lengths (reaches) of the smaller spark plug
thread size.

shown in Figure 3.19b has adapters to accommodate both thread sizes and different thread lengths. It has

a Schrader valve, very similar to a tire valve, for saving the pressure in the gauge so that the technician

can read it.

The advantage of the screw-in tester is that it can be threaded into the plug hole, leaving the technician free to crank the engine.

Breathing Problems For Engine

An engine that cannot breathe properly is suffocating and will not be able to develop sufficient compression. Engine vacuum will drop off, further lowering compression. Breathing problems can be traced to such things as worn camshaft lobes that do not open the valve far enough (Figure 3.16),or late valve timing . Valve timing can
become retarded (late) when a timing chain becomes so worn that it skips a tooth.

FIGURE 3.16 A severely worn cam lobe will not properly open a

valve.

If the timing chain has skipped and valve timing is retarded, suction will be felt at the exhaust
pipe. This happens because the exhaust valve is still open during the piston’s intake stroke.

Breathing problems can also be traced to carbon buildup around the neck of the valve (Figure 3.17)
or to restrictions such as a dirty air cleaner or a blocked exhaust.

FIGURE 3.17 A lack of carbon formation on the top of the piston,
beneath the intake valve, indicates oil leakage through the valve guide.
The valve in the photo was found when the head was disassembled

Catalytic converters in the exhaust system can become plugged after running for a prolonged period with an ignition system defect. A rich air-fuel mixture can also cause a converter to plug when it overheats and melts internally. OBD II vehicles (later than 1996) will go into limp-in mode when the computer senses a catalyst damaging misfire.


An exhaust restriction can also cause an automatic transmission to shift harshly or late due to the resulting faulty vacuum signal or increased throttle pressure in the transmission. Exhaust backpressure can be tested using a fuel pump vacuum/pressure tester connected to thesmog pump lines into the exhaust manifold, or an
adapter can be substituted for the EGR valve. According to TRW, removing the oxygen sensor to
perform the test can give an inaccurate reading due to a venturi effect in the exhaust system. Specifications
vary among manufacturers. As a general rule, pressure should not exceed 1.75 psi at wide-open throttle (WOT) under full load.

Breathing problems can also be found using a vacuum gauge


SHOP TIP
A blocked exhaust will be evident when the engine rpm is raised quickly. A roar will be heard on the engine side of the air cleaner.





SAFETY NOTE
A catalytic converter on a pre-OBDII vehicle can become so hot that it can start a fire if the vehicle is parked above dry grass.

FUEL MIXTURE PROBLEMS FOR ENGINE

Emission control and fuel system malfunctions sometimes mimic engine problems. Occasionally, important items are neglected during an engine job. Larger engine shops often employ specialists capable of diagnosing these complicated problems.

An air-fuel mixture that is too lean (too much air/too little fuel) can cause burned internal engine parts.


Oil/Fuel Wash
An overly rich mixture (too much fuel/too little air) can cause fuel wash or oil wash (when oil is washed from cylinder walls, resulting in cylinder wall wear). Leaking fuel injectors can result in cylinder wall oil wash, too. They can also cause intake valve deposits that will affect engine idle and emissions. A bad vapor canister purge valve can also cause oil wash. When only one side of a piston is worn, this is often due to oil wash. The worn side will be the major thrust side. An explanation of piston thrust surfaces is provided in Chapter 13.

(a)

(b)

(a) A burned exhaust valve like this one causes lower or no cylinder compression pressure.

(b) Severely burned valves

 Many areas use reformulated gasoline (RFG) to lower air pollution. RFG does not cause problems with
engine wear under normal conditions. But a richer than normal air-fuel mixture can result in accelerated
engine wear because the alcohol or ether in RFG dilutes the oil on the bearings, cylinder walls, and piston
rings. When mixed with the oil, it does not evaporate as easily and the diluted oil loses much of its lubricity. When a low mileage engine fails and there is no evidence of excessive dirt, abrasives, or machined material, diluted engine oil is a prime suspect.


Oxygen Sensor Problems
Modern engines use oxygen sensors in the exhaust to compare the oxygen content of the exhaust

with that of the outside air. After a short warm-up period, it gives the computer information to control
the air-fuel mixture. If the engine runs rough when cold, but the problem goes away after a short
warm-up, the oxygen sensor could be masking an air leak.
Check to see that the sensor is not dirty. Dirt or undercoating can plug the sensor’s outside air intake port, affecting the signal from the sensor. This can result in a richer than normal air-fuel mixture.


COMPRESSION LOSS
Compression loss, another reason for an engine overhaul, can be traced to two causes: compression leaks and engine breathing problems.

Compression Leaks Compression can leak due to several causes:
a blown head gasket , burned valves , worn or broken piston rings, a damaged piston , or a broken valve spring

When valve clearances are too tight the valves cannot seal against their valve seats, resulting in a compression leak. Tight valves can result from wear to the valve faces or valve seats, either of which allows the valve stem tips to move deeper into the cylinder heads. Closer valve clearance can also result
when valves have been adjusted incorrectly.
Exhaust leaks make noise at ½ crankshaft rpm

FIGURE 3.12 A damaged piston resulting from detonation

FIGURE 3.13 A broken valve spring.

FIGURE 3.14 Valve face wear will cause the valve stems to move
into the head, eliminating valve adjustment clearance

FIGURE 3.15 This broken exhaust manifold bolt resulted in a
burned exhaust valve due to thermal shock

DIAGNOSING ENGINE PROBLEMS BEFORE A REPAIR

how to troubleshoot problems on a running engine. Also discussed are some of the external causes of engine problems that allowed to continue unresolved. Internal engine  parts are shown here to illustrate some of the causes and results of these problems. Internal problem diagnosis after disassembly is also covered in more detail in subsequent chapters.
It is very important that you diagnose the cause of a problem before performing a repair. It is not
unusual for an inexperienced technician to spend many hours of work only to discover that the repair
was unnecessary.
Five major diagnosis areas are covered:
• Possible reasons for oil consumption
• Causes of rough running or a loss of engine power
• Engine noises
• Oil pressure problems
• Cooling system problems
There are many causes of engine problems. Some are the result of normal wear and tear or a lack of maintenance. Engine problems also might be due to previous work on the engine. Problems that appear to be engine-related can also be caused by other automotive specialty areas, such as the transmission or emission controls. Sometimes a problem with a system causes an engine to fail. If the problem is not taken care of, the failure will recur. This chapter should serve as a reference for future problems. The descriptions of various problems are listed in the index at the back of the book. More in-depth training in engine diagnosis comes under the overlapping specialty area of engine performance.

DIAGNOSING PROBLEMS BEFORE A REPAIR
An engine should be correctly diagnosed before disassembly for two reasons. It should be determined
that an overhaul is really necessary. The damaged starter motor drive frame shown in Figure 3.1
resulted in a diagnosis of catastrophic engine failure. Failed belt-driven accessories can also lead you to
believe that there is a seized engine. The exact location of a problem should be determined
while the engine is running. A thorough discussion of the problem with the owner of the
vehicle is also helpful. Sometimes an owner’s driving habits or maintenance procedures can be the
cause of the problem.

OIL CONSUMPTION
Piston rings are usually the first thing a customer suspects when a car starts to use oil, even though oil can be lost through a variety of other conditions. Oil loss can be due to either external leakage or internal oil consumption. Excessive internal oil consumption can sometimes be spotted as an oily coating on the inside of the exhaust pipe. Black soot at the exhaust pipe often indicates an overly rich air-fuel mixture, not oil consumption.

The rate of normal oil consumption depends on such things as the size of the engine, the weight and shape of the vehicle, the viscosity and service rating of the oil, engine rpm and load during use, engine temperature, and the amount of oxidation and dilution of the oil. Information about oil is covered in detail in Chapter 14.
From time to time an owner will complain of an occasional rapid oil loss. This might be a normal condition that sometimes occurs after 1000 or more miles of city driving followed by a highway trip. City driving can result in extra fuel and water dilution in the oil. Before leaving on a long vacation trip, the customer checks the oil and the dipstick registers “full.” But when the diluted oil becomes thoroughly heated, evaporation of the pollutants gives the appearance of rapid oil consumption as the oil level drops a quart in a few hundred miles.

Bad Valve Guides or Seals
The cause of internal oil consumption is often
worn valve guides or defective valve guide seals. There might be exhaust smoke during deceleration
because of oil leaking into the combustion chamber through the intake valve guides. Deceleration
causes very high engine vacuum, which pulls oil into the combustion chamber.
A spark plug that is oil fouled on only one side
indicates leaking valve guide seals. Carbon deposits on the necks of the intake valves are another indication . Look for carbon deposits when disassembling the cylinder head.


Different types of valve guide seals are described . Valve guide seals should always be replaced during a valve job while the heads are disassembled. includes a procedure for replacing valve guide seals without
removing the heads from the engine. Oil Consumption from Piston Rings When oil is consumed past piston rings, one common cause on high mileage engines is lack of ring tension resulting from cylinder wall and ring wear. A record of poor engine oil maintenance contributes greatly to an increased wear factor. An engine that suffers from a lack of regular oil changes will often have plugged oil control rings (Figure 3.3).

FIGURE 3.3 A Plugged oil control ring.

The piston’s oil-control rings need to be able to scrape oil from the cylinder walls and return it to the crankcase
through the underside of the piston (Figure 3.4).

FIGURE 3.4 Oil ring drainback. Slots 

(a) or holes 

(b) in the oilgroove return oil to the crankcase as the piston moves down.

Spark plugs provide a window to conditions in the cylinder because they extend into the combustion chamber. Figure 3.5 shows abnormal spark plug conditions associated with oil consumption.

FIGURE 3.5 Examples of oil-fouled spark plugs.

consumption might be caused by worn or stuck piston rings


Excessive Rod Bearing Clearance
A high mileage engine will probably have worn crankshaft bearings. Excessive bearing-tocrankshaft journal oil clearance can result in low oil pressure at idle. Oil consumption can increase at higher engine rpm as oil leaks out between the connecting rod journal and the rod bearing. At higher engine speeds, this can result in too much oil being thrown onto the cylinder walls, overwhelming the oil rings, which cannot return all of the oil to the crankcase (Figure 3.6).

FIGURE 3.6 Increased oil clearance causes more oil to be thrown onto cylinder walls

Whatever oil enters the combustion chamber will be burned with the airfuel mixture. Even with normal rod bearing clearance, high-speed driving can cause increased oil consumption due to extra oil thrown from the rods. In one test, an engine run at 70 mph used seven times the oil that it used at 40 mph.


Incorrect Engine Oil Dipstick
It is especially important to make sure that the correct oil dipstick is used after an engine change or short block installation. Manufacturers often install the same engine in different vehicle models. Depending on the vehicle, the engine can be equipped with a different oil pan, which sometimes requires a different length oil dipstick. Excessive oil consumption can result from too short a dipstick. Every time the owner mistakenly adds a quart of oil to the crankcase, the crankshaft throws the oil on the cylinder walls and the overfull engine burns off the excess.

Plugged Cylinder Head Drainback Holes
When engine oil has not been changed often enough, thick sludge can plug the oil return holes in the cylinder head. These drainback holes allow rocker arm oil to return to the crankcase (Figure 3.7). The problem can be temporarily solved by cleaning out the holes, but it is a symptom of a poorly maintained

FIGURE 3.7 Plugged oil drainback holes will cause exhaust smoke

engine and major service will soon be needed. The oil remains in the valve cover area instead of returning
to the crankcase; it floods the valve guide, making the valve stem seal ineffective.


Leaking V-Type Intake Manifold Gasket
Intake manifold vacuum can draw oil into the intake ports from the lifter-valley area under some intake manifolds (Figure 3.8). This is a tough problem to find. A smoke test is a good way of finding an intake manifold leak. A cranking vacuum is another way to test for internal air leaks before the
engine is disassembled. These procedures are covered later in this chapter. When removing an intake
manifold, always visually inspect for the possibility of previous intake gasket leakage.

V-type engines equipped with an exhaust gas recirculation (EGR) valve on the intake manifold often experience oil-fouling of the spark plugs that are closest to the EGR valve. This is caused when the intake manifold warps or the manifold gasket fails. Replace the gasket with one designed for high temperature applications.

Crankcase Pressure
Normally, there is a slight vacuum in the crankcase. One possible reason for excessive oil leakage is a positive crankcase ventilation (PCV) valve that

FIGURE 3.8 Oil can be drawn into the intake manifold past a faulty manifold gasket

To see if the PCV valve is working properly:
• Pinch the line that leads to it, or cover the end of the PCV valve with your thumb.
• With computer idle speed adjust disabled, if the PCV valve is good, idle speed should drop.
Blocking the flow of air to the PCV valve enriches the air-fuel mixture.

Be sure to check for a restricted filter or a kink in the breather line from the valve cover to the air cleaner. This can result in oil leakage caused by crankcase pressure.

If the PCV system is to be effective, the entire crankcase must remain sealed. A leaking or misplaced gasket can cause enough air leakage to result in failure of the PCV system. This includes the timing cover, oil pan, valve cover gaskets, and crankshaft seals. If the engine is not airtight, suction from the PCV valve
will not create sufficient vacuum in the crankcase. An oily air cleaner, or oil in the hose to the air cleaner,
often points to a crankcase pressure problem.

A ring seal tester can be used to test an engine’s amount of blowby. It measures airflow out of the crankcase in cubic feet per minute (cfm). Normal airflow is about 5–8 cfm. Above 8 cfm indicates that the rings are not sealing properly. Unfiltered air allows dirt to enter the engine, causing engine wear. This can result from leaking vacuum hoses, vacuum control units, vacuum accessories, or manifold leaks. Crankcase pressure
can also cause oil to migrate up the distributor shaft and into the distributor. To locate a leak in the PCV system:
• Seal the breather and PCV valve.
• Use a smoke tester (covered later) or blow (lightly) into the dipstick tube with a rubbertipped blowgun (regulated to no more than 2–3 psi). Listen for leaks, using a piece of hose or a stethoscope with the metal end pulled off.

A leak is often not readily apparent, especially at the top side of a valve cover gasket or where the
intake manifold meets the block at the front or back. Oil might not leak out because of gravity and suction
from the crankcase vacuum of the PCV system.

Oil that leaks through gaskets and seals is a common cause of oil consumption.

Rear Crankshaft Seal Leaks
A rear main bearing seal leak can be identified when oil is found on the engine side of the flywheel

or torque converter. Oil on the opposite side indicates front transmission seal leakage. Oil that has been sprayed in a circular pattern is also indicative of a crankshaft seal leak. Most crankshaft seal leaks are caused by excessive crankcase pressure.

Oil leaks streaking down the block can be due to a leaking oil gallery plug, cam plug, or seal retainer block. The block could also be porous or cracked.

Black Light Testing. When black light testing, a 1-ounce bottle of fluorescent dye is added to engine oil to help locate leaks. When a black light is used, the source of the leak will be highlighted in bright yellow-green streaks. A mirror can be used to bounce the black light into hard-to-see areas. Washing the engine first is helpful but not necessary.
There are two types of ultraviolet (UV)-fluorescent lights available. The traditional black light type uses a vapor bulb powered by 110 volts. It requires a warm-up period of about 10 minutes. With the 110-volt lamp, yellow-green dye is easily visible in the leaking oil; oil without dye appears purple. Use care when handling the lamp. The bulb is fragile and is expensive to replace. A different type of light system uses a high output 12-volt UV/blue lamp that comes on instantly and is used with yellow glasses (Figure 3.9). UV
light can be damaging to your eyes, so use caution. With the 12-volt lamp and glasses, oil is yellow and oil with dye in it is a brighter yellow-green.

FIGURE 3.9 A UV light powered by the vehicle battery
is used with yellow UV glasses, which prevent eye damage

When a leak is minor it might not show up after just a short time, so the car might need to be driven for a day or so. After the leak is repaired, the engine is cleaned and rechecked with the black light. The fluorescent dye stays in the oil. The dye is not harmful and the manufacturer says that it dissipates within 300 miles of driving powder. Refer to Chapter 16 for more information on gaskets and seals.

Tools Technicians Automotive Machinists

Hand tools must be kept in safe condition. The following are some hand tool safety considerations:
• Pounding on chisels will result in the top of the chisel folding over in the shape of a mushroom.
Do not use a mushroomed chisel until it has been reground.
• A file has one pointed end called a tang. To prevent hand injuries, install a handle on the end of a file.
• When loosening a fastener, pull toward you rather than pushing away.
• Do not use a pipe to increase leverage when tightening the handle of a vise. This can break the vise.

Puller Safety Many types of pullers, ranging from small to large, are used in automotive work. Pullers are used
to remove or install pressed-fit gears, bushings, bearings, or other parts from shafts. Specific uses of many of the pullers discussed here are covered in later chapters.
When using pullers:

• Wear eye protection.
• Be sure the pressure screw is clean and lubricated before using an impact wrench.
• Be sure the removable point is installed on the puller.
• Be sure the puller is aligned so it is perpendicular to the part being pulled.
• Do not use a puller with damaged or worn parts.
• Use the correct size puller so overloading is avoided.
• Use a three-jaw puller instead of a two-jaw puller when possible.
• When heating a part to help free it, do not heat the jaws of the puller. This could change the temper of the metal.


Press Safety
There are many special-use press fixtures available. For press work, a bearing separator plate is often used. Be sure to support it where the bolt holds the two halves of the tool together  If the separator is installed in the press 90° to the correct position, the bolts will be bent and the tool can be damaged.


Air Tool Safety
Air tools are great time-savers for technicians. In addition to blowguns, there are many air-operated
tools, including air drills, air valve seat grinding motors, air-operated valve spring compressors, and air hydraulic jacks. An air compressor provides air at a regulated pressure of 90 to 150 psi (pounds per square inch). For the best performance and reliability, air tool manufacturers recommend regulating air pressure

to 90 psi to get the longest life from air tools.

 Compressed air is very useful to a technician, but it can be dangerous when used improperly. Horseplay has no place in a shop! A blast of air can break an eardrum. Blowing compressed air into an orifice of a .person’s body can result in death. Observe the following safety precautions when using air tools:
• Always wear eye protection when blowing off parts. Pieces of debris can be blown into your eyes. Always blow down and away from yourself.
• Do not blow air against your skin; the highpressure compressed air used in auto repair shops can penetrate skin. Pressurized grease from a chassis grease gun can penetrate skin also. • Hold onto an air hose when uncoupling an air line so it does not fly through the air. When possible, bleed off the air from an air line before uncoupling an air hose. There are two basic types of blowguns . Blowguns designed for blowing off parts are regulated to produce no more than 35 psi. Rubber tipped blowguns, used to blow into fluid passageways or engine oil galleries, do not have this safety feature. A worker should not use these tools
until proper instructions on their safe use are given.

Impact Wrenches. The air impact wrench is a favorite technicians’ tool. A 1⁄2'' drive impact wrench is used to loosen large, very tight bolts. Special, extra thick impact sockets must be used with the impact wrench  Regular sockets can crack or explode  Follow these precautions when using an impact wrench:
• Be careful of loose clothing or hair that might become tangled in the tool.

• Use approved impact sockets, not chrome sockets.
• Be sure that the socket is secured to the air tool. A clip at the end of the tool’s square drive can become worn so that it no longer holds the tool.
• When the impact wrench fails to loosen a fastener, use a large breaker bar.
• When using a wobble socket, do not turn on the
impact wrench unless it is installed on a nut or bolt. The socket can fly off the impact wrench, possibly causing an injury.
Air Chisel. An air chisel is a miniature jackhammer  often used to drive valve guides
in and out of cylinder heads. There are many attachments available for a variety of uses.
When using an air chisel:
• Before pulling the trigger, be sure to have the tool bit against the workpiece. Otherwise the tool might fly out of the gun.
• Be sure to wear eye protection.
Die Grinder. Air-powered die grinders turn at very high speeds, often in excess of 20,000 rpm. Be certain


that an abrasive disk or grinding wheel used with the die grinder is rated at sufficient rpm.


General Machinery Safety
• To the eye, swiftly rotating machinery can at times appear not to be moving. Lights powered by ordinary
alternating current flicker 60 times per second. This can produce a strobe effect on moving machinery. Be cautious when working around a running engine or rotating machinery. Fingers can be severed by a moving belt and pulley.

• Do not talk to someone who is operating a machine; do not talk to someone when you are operating a machine.

Drill Safety
• Always wear eye protection.
• Release pressure occasionally to allow chips to break off before they become too long and dangerous.
• A drill bit may catch when it starts to break through the bottom of the work being drilled. Be sure that sheet metal is clamped to the worktable. Let up the pressure on the bit as it starts to break through the bottom of the hole.
• If the drill grabs the work, shut off the drill. Never grab the moving work.
• Never stand in water when drilling. Standing in water increases the danger of electrical shock.
• Be sure to remove the chuck key from the chuck before drilling. Grinder Safety
• Stand to the side when starting the motor. The grinding wheel is more likely to explode during startup because of the inertia of the wheel.
• Wear face protection.
• Position the tool rest as close to the wheel as possible, so that nothing can get trapped between the wheel and the tool rest
• Do not grind on the side of the grinding wheel.


LIFTING EQUIPMENT
Automotive repair work includes lifting heavy items like engines, transmissions, and entire vehicles. Safe lifting practices will prevent accidents and injuries. Hydraulic Jacks A hydraulic floor jack  is used to raise and lower the vehicle and to help position heavier components, such as engines and transmissions.
Position the jack under the vehicle frame, or at one of the correct lift points shown in the service literature  Many vehicles are built

Engine Shop Safety

An engine shop has many tools, pieces of equipment, and chemicals. This chapter deals with their proper uses and safe shop practices. The number one priority of any business should be the health and safety of its employees. Those safety issues are covered here first, followed by a safety test at the end of the chapter. The information provided will help you understand how to protect yourself from hazards in the workplace. You will also gain insight regarding the impact of safety laws on your employer.

As you read this chapter, realize that the situations described can and do occur, sometimes often. Case histories presented throughout this tips are true. Pay extra attention to the safety precautions detailed with each piece of equipment. Chemical safety is covered in this chapter as well.

GENERAL SHOP HEALTH AND SAFETY
When an accident occurs in an automotive shop, it is perhaps because safety considerations are not as
obvious when repairing automobiles as they are in other trades like roofing or carpentry. This is sometimes
the reason why people get hurt. Accidents are often caused by carelessness resulting from a lack of
experience or knowledge. Often someone other than the one who has been injured causes the accident and suffers from the guilt of knowing the harm that he or she has caused. In the event of an accident, inform your instructor or supervisor, who will know what procedures to follow to ensure your safety. Injured persons often suffer from shock.
When an injury does not appear to be serious enough to call an ambulance, another person should be sent with the injured person to seek professional help. Every shop should have someone trained to handle
emergencies. The American Red Cross offers thorough first-aid training.

General Personal Safety
A first-aid kit  contains items for treating some of the small cuts and abrasions that occur on a regular basis. Fires and accidents involving equipment like lifts and battery chargers happen occasionally in automotive shops. However, the most common injuries involve the back or the eyes, which are injuries that are largely
preventable.

Eye Protection
Eye injuries are one of the most common injuries in an automotive shop, so continual use of glasses is recommended. Eye protection is emphasized for your own good, so use common sense. Several types of eye protection are shown in Figure 2.2.

FIGURE 2.2 Eye protection. (a) Goggles. (b) Face shield.

(c) Safety glasses.

Safety glasses or a face shield must be worn when using equipment. Face shields are convenient because they can be stored with each piece of equipment. They are also easily adjustable to your head. Using a hydraulic press or pounding with a hammer can cause parts to explode and rotating tools can throw pieces of metal or grit, causing eye injuries. Prescription safety glasses are an advantage because the user always wears them.

Wearing eye protection will prevent most eye injuries. Eye protection must be worn:

• whenever working around moving parts and machinery.
• when blowing off parts with compressed air.
• when working on air conditioning. Refrigerant
contained in the air-conditioning system will instantly freeze anything with which it comes into contact. If it gets into your eyes, blindness can result. Additional cautions about skin and eye protection are covered


Back Safety
Protect your back when lifting. Following safe lifting procedures will prevent most back injuries. The normal tendency is to think that items are not that heavy, so you do not ask somebody for help. Be sure to get help when moving heavy items. If something is in an awkward position for lifting, leverage and the position your back is in can make it easier for an injury to occur. Before moving a heavy item, plan the route that the item will be carried and how you will set it down when you get there.
• If an item is too heavy to lift, use the appropriate equipment.
• Lift slowly.
• Do not jerk or twist your back. Shift your feet
instead.
• Bend your knees and lift with your legs, not
your back (Figure 2.3). Also, keep your lower back straight when lifting. Think about thrusting
your stomach out.

FIGURE 2.3 Lifting precautions.

Ear Protection
Damage to your hearing happens when you are exposed to loud noise over a period of time. A good
rule of thumb is “if you feel any discomfort from noise, you are probably hurting your hearing.”
When loud machinery and air tools are used, ear protection should be worn.


Shoes or Boots
Leather shoes or boots offer much better protection than tennis shoes or sandals. Some soles are
resistant to damage from petroleum products, and the tread can be designed to resist slipping. Boots
and shoes that have the toe reinforced with steel inserts are widely available. An additional incentive
is that safety footwear is often deductible from a technician’s or machinist’s income taxes.

SHOP CLEANLINESS
Good housekeeping practices are essential when cleaning engine parts and should be carried out
throughout the rebuilding process and engine installation. A clean, orderly shop is vital for impressing
on the public that your professional repair facility is thorough and competent. Of even more importance,

however, is the health and safety of anyone in the shop area.


Shop Towels
A shop is cleaner if its technicians use shop towels when working. Greasy, oily tools and hands
should be wiped clean, preventing the mess from being spread around the rest of the shop. Most
shops have linen service for uniforms and shop towels. Shop towels are often dyed red so the linen
company can tell when they have come into contact with battery acid, which leaves blue marks on red
towels

Spills and Oil Leaks

Slippery floors are dangerous. To avoid the possibility of a dangerous slip and fall, immediately clean up slippery spills like coolant, solvents, glass  beads, or steel shot. Preventing spills from occurring

in the first place is best, but when spills do occur, they must be dealt with immediately.
• Cleaning up a mess will prevent it from spreading around the shop.

FIGURE 2.6 When drying parts with compressed air, blow solvent

back into the solvent tank.

• Parts that are wet with solvent should be blown off into the solvent tank (Figure 2.6) or allowed to air dry before being moved.
• Wet parts can be carried from the solvent tank in a drain pan to prevent solvent from dripping
onto the floor (Figure 2.7).

FIGURE 2.7 To avoid dripping solvent on the floor, carry wet parts in

a drain pan

• An engine should be drained of oil and coolant before removing it from the vehicle. The oil filter holds oil, so it should be removed, too. The oil and filter will need to be disposed of properly in accordance with governmental requirements.


Absorbing Spills
To prevent someone from slipping, clean oil spills immediately with greasesweep  an already soiled shop towel, or absorbent mats or pads. Greasesweep is an absorbent material like rice hull ash or kitty litter. It is swept up and reused until it becomes too wet. In fact, it works better when slightly wet because the dust that results when using new greasesweep is avoided.
Greasesweep becomes a hazardous material after it is used to soak up used motor oil or spilled

fuel. Bioremedial oil-absorbent products are newer materials sometimes used instead of greasesweep.
These products have microbes that “eat” oil or fuel, converting them to harmless carbon dioxide (CO2)
and water. Concrete floors cleaned with this material are left clean and slip resistant. A major advantage
to this method is that the need for hazardous disposal is reduced or eliminated. Superabsorbent cloths are available from waste disposal companies for soaking up spills. The disposal company collects the soiled cloths for proper treatment. There are also nontoxic water-based degreasers


FIRE PREVENTION
Some common sense is important when dealing with fires. If the fire is burning so dangerously that
your personal safety is jeopardized, withdraw from the area immediately and call for help. But if you can
safely remove the source of fuel to a fire, do so. This might include shutting off fuel to a fuel fire or disconnecting the electrical source from an electrical fire.


Fire Extinguishers
A fire extinguisher is a portable tank that contains water or foam, a chemical, or a gas .
There are four kinds of fires, each calling for a different type of fire extinguisher

• A Class A fire is one that can be put out with water. Such things as paper and wood make up these kinds of fires.
• A Class B fire is one in which there are flammable liquids such as grease, oil, gasoline, or paint. • A Class C fire is electrical.
• A Class D fire involves a flammable metal such as magnesium or potassium.
• Either CO2 or a dry chemical fire extinguisher can be used on Class B and Class C fires.

A popular fire extinguisher is the 2-A:10-B:C. You can find this information on the label. For car fires, fire officials recommend an extinguisher no smaller than this. An extinguisher with the number 1-A:5-B:C would be one-half as big. The 1 is the size for the A (water) type of that extinguisher. The 5 is the size for Class B (flammable liquids) and C (electrical parts fires). This extinguisher does not work on Class D fires. Locate and check the type of fire extinguisher(s) in your shop. They should not be located in a place where a fire is likely to start. For instance, do not mount a fire extinguisher right over the welding bench or next to the solvent tank. If a fire began in either of these places, you would not be able to get to the fire extinguisher.

A gauge on the top of the fire extinguisher tells whether it is fully charged or if the charge pressure has leaked off. Fire extinguishers in business establishments are routinely inspected by the local fire department.


Flammable Materials
Greasesweep and shop towels soaked in oil or gasoline should be stored in covered metal containers
 Keeping oil materials separated from air prevents them from self-igniting, a process called spontaneous combustion. Used greasesweep is kept in a flammable storage container because it is reused until it becomes saturated (wet). Flammable materials that are not in approved containers must be stored in a flammable storage cabinet .


Fuel Fires
Gasoline is a major cause of automotive fires. Liquid gasoline is not what catches fire. Rather, it is the vapors that are so dangerous. Gasoline vapors are heavier than air, so they can collect in low places in the shop. They can be ignited by a spark from a light switch, the motor, electrical wires that have been accidentally crossed, or a dropped shop light. Two kinds of shop lights are acceptable. One has a fluorescent bulb enclosed in a plastic tube. The other uses a special spark-proof incandescent bulb.


Electric Shock
Twelve-volt direct current (DC) electrical systems like the ones used in automobiles are not capable of inducing serious electrical shock, unless the engine has a distributorless ignition or is a highvoltage hybrid. Shop equipment, however, is powered by either 110-volt or 220-volt alternating current. Electric shock hazards can be minimized when using electrical tools by not standing in water. To prevent a spark from jumping from the outlet to the plug, be sure that a tool is not in the “on” position before you plug it into the outlet.
Three-wire electrical tools are the best choice for commercial work. The extra terminal is connected
to ground (Figure 2.14). If you use a homeownertype tool with a two-wire plug, it should be double
insulated. Traditional automotive wiring color is black for ground and red for positive, but in commercial
wiring the green wire is for ground.


Coolant Burns
The most likely way to be burned in an automotive shop is with superheated engine coolant. Opening the radiator on a hot engine can be very dangerous. Always squeeze the top radiator hose  before opening a radiator cap .If the hose is hard and feels like it is full of coolant, the coolant level is acceptable. If the hose collapses, there is no pressure on the coolant but steam can still cause a burn, so exercise extreme caution when opening the cap.
CASE HISTORY

A student had just started working in a repair shop. A customer asked him to check the radiator coolant level. When the student opened the radiator cap, he turned it one-half turn. The coolant boiled out into the coolant overflow tank, where it escaped, burning him and wasting the coolant . The radiator cap maintains pressure on the coolant when the engine heats up. Coolant’s boiling point is higher when it is under pressure.
Loosening the cap removes the pressure, causing the coolant to boil instantly and violently


Cooling Fans
The fan that draws cool air into the radiator can be belt driven or electric. Rotating fans can be dangerous

One of the most common farm injuries is lost fingers because farm machinery has many belts. Fingers
are often cut off when they are caught between a belt and pulley. Before attempting a fan belt adjustment, be sure that the keys are out of the ignition. If someone cranks the engine over, fingers can be cut off. Be certain that a helper understands what you are asking him or her to do. Assuming that your helper understands can result in an accident.


Safety Check before Test Drive
Before driving a customer’s car, remember to check the operation of the brakes and condition of the tires. Do not test drive a car with obvious safety hazards until they have been corrected. It makes no sense to test drive a car with dangerous brakes.

Difference Cam-in-Block or Overhead Cam

 Some I-head engines have the camshaft located in the block. This engine design is called a pushrod engine, or cam-in-block engine. Cam lobes raise valve lifters that act on pushrods to operate rocker arms and open the valves (Figure 1.31). In late-model vehicles, pushrods are found most often on V-type engines.

A more popular type of valve operating arrangement for late-model engines is the overhead cam design, or OHC. This engine has the camshaft mounted on top of the cylinder head just above the valves (Figure 1.32a). It has the advantage of having fewer parts and less weight. An engine running on the freeway at 3000 rpm has to open and close a valve 25 times per second, so valvetrain weight is very important. It is even more important in high-speed engines.

Some OHC engines have a single cam (SOHC). Each cylinder is provided with two separate lobes to operate the intake and exhaust valves. Highperformance OHC engines often have two cams per cylinder head. On this design, known as dual overhead cam (DOHC), one camshaft operates the intake valves and the other operates the exhaust valves (Figure 1.32b). DOHC engines have become more common in recent years as the base engine of many vehicle manufacturers.

The OHC engine uses a long chain or belt from the crankshaft to the cylinder head to drive the cam(s)     (Figure 1.33). When the ignition system uses a distributor, some OHC engines use an auxiliary shaft to drive it, whereas others have a crankshaftdriven distributor.

FIGURE 1.32 In-line four cylinder overhead cam engine.
(a) An OHC engine with the cam positioned over the valve. (b) A dual overhead cam (DOHC)
engine.

FIGURE 1.33 V-type overhead cam engines. (a) Belt-driven

overhead cam V6. (b) Chain-driven overhead cam V8

Learn Short Block and Long Block

Short Block and Long Block The cylinder block assembly (without the heads installed) is called a short block. The short block includes the crankshaft, piston and rod assembly, and all bearings. On pushrod engines, the camshaft, timing sprockets, and timing chain are also part of the short block (Figure 1.22).

FIGURE 1.22 Exploded view of a short block for a cam-in-block
engine.

The lower area of the cylinder block surrounded by the oil pan is called the crankcase because the crankshaft is located there. Main bearing bore holes are precisely align-bored in the lower end of the block to provide a mounting place for the main bearings and crankshaft. Main bearing caps are removable, but they must be replaced in exactly the same location. At the factory, the camshaft bore holes, cylinder bores, cylinder head mounting surface, all threaded holes, and all gasket surfaces are machined automatically and in
perfect alignment to each other. During rebuilding, the technician or machinist’s job is to maintain
the original alignment.

The following lists typical components common to both short and long blocks:

• Oil Pan. The oil pan is a stamped sheet metal or cast aluminum part that encloses the crankcase (Figure 1.23). It provides a reservoir where the engine oil is cooled as air passes across its surface. Oil pans are sometimes damaged when driving or during engine removal and replacement. Sometimes a sheet metal oil pan can be bent enough so that the crankshaft comes in contact with it. After a rebuild, the resulting noise can cause a great deal of worry when the engine is first started.

FIGURE 1.23 The oil pan encloses the crankcase

• Flywheel. Mounted on the rear of the crankshaft is a flywheel or flexplate. The weight of the flywheel helps carry the crankshaft beyond BDC after the power stroke and smoothes out the power impulses of multiple cylinders. A flywheel is used with a standard transmission. It also provides a surface for the clutch to work
upon. When the vehicle is equipped with an automatic transmission, a torque converter and flexplate are used (see Chapter 4). A ring gear on the circumference of the flywheel or flexplate provides a gear drive for the starter motor. Ring gears on flywheels and flexplates are sometimes
damaged by faulty starter motors. Replacement of a flywheel ring gear or a flexplate is a relatively easy job while the engine is out of the vehicle.

• Vibration Damper. The vibration damper, also called a harmonic balancer, is mounted on the front of the crankshaft on V-type and in-line six cylinder engines. The power impulses on the pistons cause the crankshaft to twist and untwist in much the same manner as a tuning fork vibrates. The damper dampens out these torsional vibrations, which could result in a broken crankshaft if allowed to continue. Most four cylinder engines do not require a damper and use only a pulley.

• Crankshaft. The crankshaft is made of either cast iron or forged steel. Its bearing surfaces for the main and rod bearings are called journals. The main bearing journals are those that run down the centerline of the crankshaft, in line between the front and rear journals. Oil galleries provide lubrication to the main bearing journals through oil holes in the main bearings. Holes are drilled in the crankshaft, from the main bearing journals to the connecting rod bearing journals, to provide the rod bearings with pressurized
lubrication. Rod journals, also called crankpins, are offset 90° on V8s, 180° on four cylinders, and 120° on six cylinders (Figure 1.24). Some V6s have offset crankpins

FIGURE 1.24 Crankshaft rod journals are offset 180° for four cylinders, 120° for six cylinders, and 90° for eight cylinders

exhaust emissions are produced because of the smaller amount of surface area in the combustion chamber. When cool engine surfaces are exposed to unburned fuel, a skin effect occurs and the unburned fuel ends up in the exhaust stream. Increasing the valve opening, called valve lift,
to a certain point is necessary to allow enough airfuel mixture into the cylinder to develop maximum power. Increased valve lift is possible with the I-head engine design. This is because as the intake valve opens, the piston is moving down in the cylinder, providing clearance. When the exhaust valve is wide open, the piston is near the bottom of the cylinder, providing plenty of pistonto- valve clearance as well. If more air-fuel mixture is packed into the cylinder, more power will be developed. This is called volumetric efficiency, which is the reason that supercharging is so effective in producing extra power from relatively small engines. In supercharged engines, an air pump compresses more air-fuel mixture into the cylinder

VINTAGE ENGINES
Until the early 1950s many automobiles had L-head engines whose valve configuration
resembles the letter L upside down . These engines, also called flatheads or sidevalves,
are still used in lawnmowers, generators, and other industrial engines. L-head engines are less expensive
to manufacture, but they produce more smog due to the high amount of surface area exposed to
unburned fuel. Flatheads are also limited in their compression ratio and valve lift. Increased valve lift
requires more clearance in the combustion chamber, which would lower compression. shows an L-head Studebaker engine with the cylinder head removed.
Notice how the valves are located in the block. Flatheads were very popular with early hot rodders
and racers  A popular hot-rodding trick was to remove the cylinder head (a relatively
easy thing to do) and mill it to increase the compression ratio

FIGURE 1.29 A flathead Studebaker block with the head removed

 

FIGURE 1.30 A flathead V8 engine from a vintage dragster.