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When doing a cylinder balance test, you come up with the following results. Cylinder RPM drops from 650 to 1 575 2 560 3 630 4 570 Predict which cylinder is not producing power. The manufacturer requires at least a 10% drop in RPM when a cylinder is killed. Complete the following chart. Cylinder Percentage of Drop 1 2 3 4 According to your calculations in the above chart, which cylinder is not producing power? Solution Student predictions: Answers may vary. Cylinder Percentage of Drop (rounded to nearest tenth of a %) 1 (650 � 575)/650 = 75/650 = 11.5% 2 (650 � 560)/650 = 90/650 = 13.8% 3 (650 � 630)/650 = 20/650 = 3.1% 4 (650 � 570)/650 = 80/650 = 12.3%

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When doing a cylinder balance test, you come up with the following results.

Cylinder RPM drops from 650 to1 5752 5603 6304 570

Predict which cylinder is not producing power.

The manufacturer requires at least a 10% drop in RPM when a cylinder is killed. Complete the following chart.

Cylinder Percentage of Drop1234

According to your calculations in the above chart, which cylinder is not producing power?

Solution

Student predictions: Answers may vary.

Cylinder Percentage of Drop(rounded to nearest tenth of a %)

1 (650 � 575)/650 = 75/650 = 11.5%2 (650 � 560)/650 = 90/650 = 13.8%3 (650 � 630)/650 = 20/650 = 3.1%4 (650 � 570)/650 = 80/650 = 12.3%

10% drop of original amount = (0.10)(650) = 65 rpmAcceptable amount must be (650 � 65) = 585 rpm or less.

Cylinder 3 is not producing power. 3.1% < 10%630 rpm > 585 rpm

A good engine will have a fairly even compression from cylinder to cylinder. If the highest and lowest readings vary more than 25% of the highest reading, the engine should be repaired.

Compression readings for a 4-cylinder engine are shown below. Determine if the engine compression range is within recommendations.

  Cylinder 1   Cylinder 2   Cylinder 3   Cylinder 4  173   180   147   128

Which, if any, cylinder would you perform a cylinder leakage test on?  Please explain.SolutionThe highest reading is 180.25% of the highest reading = (0.25)(180) = 45The cylinders should be between (180 � 45) = 135 and 180.You need to perform a cylinder test on cylinder 4 since 128 is less than 135.

You measured free height of a set of valve springs and have come up with the following:

Spring Height (inches) Acceptable Not Acceptable

1 1 7/8

2 1 15/16

3 1 3/4

4 1 7/8

5 1 13/16

6 1 29/32

7 1 31/32

8 1 15/16

The manufacturer�s spec for free height is 1 7/8 inches ± 1/16 inch.  Check each spring in the table above and determine whether each is acceptable or not.

Solution:

The range of acceptable springs is as follows:1 7/8" + 1/16" = 1 14/16" + 1/16" = 1 15/16"1 7/8" � 1/16" = 1 14/16" � 1/16" = 1 13/16"(1 13/16" < spring height < 1 15/16")

Spring Height (inches) Acceptable Not

Acceptable1 1 7/8 X2 1 15/16 X3 1 3/4 X4 1 7/8  X5 1 13/16  X6 1 29/32  X7 1 31/32 X8 1 15/16  X

If the inside diameter of the guide you have measured is 0.3458� and the outside diameter of the valve stem is 0.3413�, what is the valve stem-to-valve guide clearance?

The maximum valve guide clearance is 0.0015".  Is this exhaust stem-to-valve guide clearance within service specifications?

Solution:

0.3458 � 0.3413 = 0.0045/2 = 0.00225"

This is not within specifications since 0.00225" > 0.0015".

Find the difference between the major and minor diameter of the following components.

Type Major Diameter

Minor Diameter

Difference

Valve Stem 0.375� 0.368�Cylinder Bore 3.692� 3.686�Crank Shaft Journal

2.499� 2.4965�

Cam Lobe 25.67 mm 20.86 mmCylinder Bore 93.77 mm 93.624 mm

Solution:

Difference is Major Diameter minus Minor Diameter.

Valve Stem:  0.375 �0.368 = 0.007"Cylinder Bore:  3.692 � 3.686 = 0.006"Crank Shaft Journal:  2.499 � 2.4965 = 0.0025"Cam Lobe:  25.67 � 20.86 = 4.81 mmCylinder Bore:  93.77 �- 93.624 = 0.146 mm

Read the following 17 micrometer measures.  Label your answers with the appropriate units.

Metric Micrometer Readings

American Standard Micrometer Readings

Solution:

Metric:                           American:1.  14.10 mm               1.   0.230 in2.  10.14 mm               2.   0.364 in3.  15.29 mm               3.   0.554 in4.  24.25 mm               4.   0.635 in5.  18.43 mm               5.   0.608 in6.  13.18 mm               6.   0.323 in7.  10.14 mm               7.   0.459 in8.  13.03 mm               8.   0.803 in9.  22.18 mm

The amount of wear that has taken place on a camshaft may be determined by taking two measurements of a cam lobe.  One measurement dimension A, is across the cam lobe and the other, dimension B, is across the base circle (see figure below).  The lobe lift is determined by subtracting the B measurement from the A measurement.

The cam lobe dimension A is 35.90 mm and dimension B is 29.25 mm.  What is the lobe lift?

Solution:

The lobe lift is the difference between the cam lobe dimension A and dimension B.35.90 mm � 29.25 mm = 6.65 mm

The outside diameter of a camshaft bearing journal is 1.125" and the inside diameter of the installed bearing measures 1.1273�.  How much clearance is there?

Solution:

The amount of clearance is one-half the difference between the inside and the outside diameters.1.1273" � 1.125" = 0.0023"0.0023"/2 = 0.00115"

You are doing an engine repair that requires the removal of a piston.  Before you remove the piston, you must first measure the ring ridge.  If the ring ridge is greater than 0.1 millimeter, it must be removed before the piston is removed.  The top measurement in the unworn part of the cylinder is 88.925 mm.  The measurement in the worn part of the cylinder is 89.103 mm.

 1.  What is the difference in the measurements you made?

 2.  Should the ring ridge be removed before the piston is removed?  Explain your answer.

 

 

 

 

Solution:

1.  Ring ridge = 89.103 mm � 88.925 mm     Ring ridge = 0.178 mm

2.  Yes.  Since 0.178 mm > 0.1 mm, the ring ridge must be removed before the piston is removed

A 4-cylinder Honda has a bore of 8 cm and a stroke of 9.1 cm. Find the piston displacement in cubic centimeters. Use the formula Vd = 0.785 x d2 x s x nwhere: d is the bore or diameter of the pistonv is the volume of the cylinderss is the stroke or piston travel lengthn is the number of pistons

Solution

Vd = 0.785 x d2 x s x nVd = (0.785)(82)(9.1)(4)Vd = (0.785)(64)(9.1)(4)Vd = 1828.736 Vd= 1829 cubic centimeters

- 88.825 -

- 89.103 -

What is the total piston displacement (cubic inches) on an 8-cylinder engine with a 3 ½ inch diameter and a 4 3/8 inch stroke? Round your answer to the nearest whole number. Use the formula Vd = 0.785 x d2 x s x nWhere:d is the bore or diameter of the pistonv is the volume of the cylinderss is the stroke or piston travel lengthn is the number of pistons

SolutionVd = 0.785 x d2 x s x nVd = (0.785)(3.52)(4.375)(8)Vd = (0.785)(12.25)(4.375)(8)Vd = 336.56875Vd = 337 cubic centimeters

Problem:

An engine leaks 1/10 ounce drop of oil every 4 seconds at the rear seal. How many hours will the engine run before you have to add 1 qt of oil?

Solution:

1 qt = 32 oz1/10 = 0.1You lose 0.1 oz every 4 seconds.

So,  ,   or 

and x = 40.32 or x = 1280 seconds1280 � 60 = 21.3 mi

What is the engine displacement in cubic inches on an 8-cylinder engine 4.6 liter engine with a cylinder bore diameter of 3 ½ inch a piston stroke length of 4 3/8 inch?

Solution

Calculate the volume of one cylinder.V = r2lV =()(3.5/2)2(4.375)V =()(1.752)(4.375)V =()(3.0625)(4.375)V = 42.09243282The volume displacement for one cylinder is approximately 42.09 in3.

Calculate the total volume of all eight cylinders.(42.09)(8) = 336.72The total engine displacement is 336.72 in3.

Problem:

1. When filling a 15-quart system with a solution that is 40% water and 60% coolant, how many quarts of coolant would be required?

2. The chart below shows the relationship between the boiling point and freezing point of ethylene glycol coolant and the percent antifreeze coolant content of the coolant. According to the following chart, if you had a 15-quart system that contained 9 quarts of antifreeze and 6 quarts water what would the boiling point of the antifreeze in the system be?

Antifreeze Boiling and Freeze Protection Chart Percent Antifreeze Freezing Point (°C) Boiling Point (°C)

49%50%60%70%

�24�37�52�64

126129132136

Conditions: 100 kilopascals (15 psig) radiator cap in good condition

Solution:

1. 40% of 15 = (.40)(15) = 66 qts water15 � 6 = 9 qts of coolant

2. 132°C @ 60% from chart

Problem:

Joe's Auto Repair shop ordered parts totaling $418.90. The supplier requires 25% down and 5% for shipping with each order. If Joe plans to send $125, will that amount be sufficient?

Solution:

A = (25%)(418.90) + (5%)(418.90)A = (30%)(418.90)A = (0.3)(418.90)A = 125.67No, $125 will not be sufficient. Joe needs to send $125.67.

If a panel is 0.031 inch (0.79 mm) thick and you grind off 0.024 inch (0.61 mm) of metal, how thick is the remaining panel measured in inches and in millimeters?

Solution:

Customary: 0.031 � 0.024 = 0.007 inchMetric: 0.79 � 0.61 = 0.18 mm

Problem:

As a technician you are frequently asked to repair older model vehicles. A customer has brought into your shop an older car, whose value is listed as $2250, needing repairs to its suspension system resulting from an accident. After diagnosing the problem, you calculate that the parts needed for the repairs will be $1250. In addition, you calculate that it will take you 29 hours (at $35.00/hour) to complete the repairs. What is your advice to the customer? Go ahead with the repairs or "total" the car?

Solution:

$1250 + ($35/hour � 29 hours) = ?$1250 + ($1015) = $2265

The customer should "scrap" the car; the cost of the repairs ($2265) exceeds the value of the car ($2250).

What is the engine displacement in cubic inches on an 8-cylinder engine 4.6 liter engine with a cylinder bore diameter of 3 1/2 inch a piston stroke length of 4 3/8 inch?SolutionCalculate the volume of one cylinder.V = r2lV =()(3.5/2)2(4.375)V =()(1.752)(4.375)V =()(3.0625)(4.375)V = 42.09243282The volume displacement for one cylinder is approximately 42.09 in3.Calculate the total volume of all eight cylinders.(42.09)(8) = 336.72The total engine displacement is 336.72 in3.

Problem:An auto parts distributor drives 129 miles on Monday, 135 miles on Tuesday, and 219 miles on Wednesday.What was his average mileage for those 3 days?Solution:(129 + 135 + 219)/3 = 161 miles

Problem:

As an auto body repair person, you are asked to make repairs on a car that has been involved in a serious accident. Damage was sustained to the left front fender, as well as the right headlight, turn light, right fender, and right quarter panel. After consulting parts books and according to your calculations, these are the labor and parts costs:

Labor (non-taxable)14 hours for repairs and repainting�$27.50/hour2 hours of washing and waxing�$9.50/hour

PartsPaint�$105Headlight�$85Turn light�$55New fender�$265New quarter panel�$625Washing/waxing materials�$11.50

Discount on parts only (if paid in cash)8.75%

Sales tax (on taxable items only)6% 

If the customer pays cash, how much will the repairs total?

Solution:

Labor(14 hours)($27.50 per hour) = $385(2 hours)($9.50 per hour) = $19$385 + $19 = $404

PartsPaint�$105Headlight�$85Turn light�$55New fender�$265New quarter panel�$625Washing/waxing materials�$11.50$105 + $85 + $55 + $265 + $625 + $11.50 = $1146.50

($1146.50)(8.75%) = (1146.50)(0.0875) = 100.31875Cash discount = $100.32

$1146.18 � $100.32 = $1046.18 for parts reflecting cash discount($1046.18)(6%) = (1046.18)(0.06) = 62.7708Sales tax = $62.77

$404 + $1046.18 + $62.77 = $1512.95 Total

A technician is overhauling a 6-cylinder engine with a bore of 3.800 inches and a stroke of 3.4 inches. Due to wear the engine block must be bored out 0.030. What will the new cubic inch displacement of the engine be when finished?

(Hint: Cylinder cubic inch =   · stroke · cylinder)

 

Solution:

156.6/4 * 6 = Cubic inch displacement

39.15 * 6 = Cubic inch displacement

234.9 = Cubic inch displacement

The distance from the floor to the clutch pedal in the released position is 6 7/8�.  When the pedal is pushed to the end of its free play range, the distance to the floor measures 5 3/8�.  The clutch pedal free play should measure one to two inches.  What is the free play?  Is it within the specs?

Solution:

The free play is 6 7/8" �- 5 3/8" = 1 4/8" = 1 1/2"

Yes, 1 1/2" is within the specifications of one to two inches.

1" < 1 1/2" < 2"

Problem:

How fast will a car be traveling at 3000 rpm in

a) 3rd gear?b) 4th gear?c) 5th gear?

Given:3rd gear ratio:4th gear ratio:5th gear ratio:Rear axle:Tire diameter:1 mile:

1.25 : 11 : 10.7 : 13.73 : 125 inches5280 feet

Solution:Engine-to-transmission ratio is 1.25 : 1.

So,  , 3000 = 1.25 t, or   = t = 2400 rpm transmission.

Transmission-to-rear axle ratio is 3.73 : 1.

So,  , 2400 = 3.73 RA or   = RA = 643 rpm rear axle.

Revolutions/hr: 643 rpm � 60min/hr = 38,580 rev/hr

Tire circumference: 25 inches � 3.14 = 78.5 inches

Speed: 38,580 rev/hr � 78.5 = 3,028,530 inches/hr

Speed: 3,028,530 inches/hr � 12 in/ft = 252,377.50 ft/hr

Speed: 252,377.50 ft/hr � 5280 ft/mile = 47.8 miles/hr4th Gear: 59.8 mph5th Gear: 85.4 mph

You are doing a four-wheel alignment on a customer�s vehicle.  During the alignment, you made the following toe measurements.

Tire Distance from centerline of vehicle to Calculate tire toe 

Centerline of the tire at the front of the tire

(A)

Centerline of the tire at the rear of the tire 

(B)A – B

Right Front 71.3079 cm 71.8921 cm

Left Front 71.8413 cm 71.3587 cm

Right Rear 71.9048 cm 71.2952 cm

Left Rear 71.4984 cm 71.7016 cm

a.  Complete the table by calculating the toe on each tire.  Express answers in millimeters.

b.  Calculate the total toe on the front end by finding the sum of the right front toe and the left front toe.

c.  Calculate the total toe on the rear end by finding the sum of the right rear toe and the left rear toe.

 Solutions:

   a. 

Calculate Tire ToeA – B

–5.842 mm4.826 mm6.096mm

–2.032 mm

b.   Total toe on front end = –5.842 mm + 4.826 mmTotal toe on front end = –1.016 mm

c.      Total toe on rear end = 6.096 mm + (–2.032 mm) Total toe on rear end = 4.064 mm

Source: AYES

According to the following chart, if I have a 14-quart capacity cooling system and I want to obtain protection against freezing down to about �54 degrees Fahrenheit, how many quarts of antifreeze should I have in the system?

Antifreeze & Coolant Means Maximum Severe Conditions Protection

Cooling System Capacity in Quarts 3 4 5 6 7 8 9 10 11

8 �7 �34 �69

9 0 21 �50 �70

10 4 �12 �34 �62

11 8 �6 �23 �47 �65

12 10 0 �15 �34 �57

13 3 �9 �25 �45 �64

14 6 �5 �18 �34 �54 �68

15 8 0 �12 �26 �43 �62

16 10 2 �8 �19 �34 � 52 �64

17 5 �4 �14 �27 �42 �58 �69

18 7 0 �10 �21 �34 �58 �62

19 9 2 �7 �16 �28 �42 �56

20 10 4 �3 �12 �22 �34 �48

Solution:

Reading from the chart:Go down to 14 quarts, and over to �54 degrees.The answer is 8 quarts.

Use the chart below to answer the following question.  How many quarts of antifreeze coolant are needed for a 4-gallonsystem to �34°F?                      (1 gallon = 4 quarts)

 

Cooling System

Capacity in

Quarts

              Quarts of Antifreeze required for protection to Temperatures (°F) shown

2 3 4 5 6 7 8 9 10 11

5 �12 �62

6 0 �-34

7 6 �17 �54

8 �7 �34 �69

9 0 �21 �-50 �70

10 4 �12 �-34

�-62

11 8 �6 �23 �47 �65

12 10 0 �15 �-34 �57

13 3 �-9 �25 �45 �-64

14 6 �-5 �18 �-34 �54 �68

15 8 0 �12 �26 �43 �-62

16 10 2 �8 �19 �34 �-52

�-64

17 5 �4 �14 �-27 �42 �58 �69

18 7 0 �10 �-21 �34 �50 �62

19 9 2 �7 �16 �28 �-42 �56

20 10 4 �3 �12 �22 �34 �48

21 6 0 �9 �17 �28 �41

22 3 2 �5 �14 �23 �-34

Solution:

Since one gallon is equal to four quarts, then four gallons equals 16 quarts. (4)(4) = 16

Reading off of the chart, 16 quarts at �34-degrees Fahrenheit requires 8 quarts of antifreeze.

The chart below shows the relationship between the boiling point of coolant and the percent antifreeze coolant content of the coolant.

Percent Antifreeze in Coolant Boiling Point of Coolant (°F)

0 21210 21320 21430 21740 22350 22860 23670 24580 25890 270

100 330

You have tested a car�s coolant system and found that the coolant is 20% antifreeze.  The car will hold 12 liters of antifreeze when full.

a.   What is the boiling point of the coolant in the car with coolant containing 20% antifreeze?

b.  If you want the boiling point to increase to 245°F, what percent antifreeze should the coolant be?

c.  How many liters of coolant should you remove from the system so that replacing by 100% antifreeze will raise the boiling point to 245°F?

Solution:

a.  Reading off of the chart, the boiling point is 214°F.

b.  Reading off of the chart, the percent of antifreeze is 70%.

c.  original amount = new amount     0.20(12 – x) + x = (12)(0.70)    2.4 – 0.20x + x = 8.4    2.4 + 0.80x = 8.4    0.80x = 6    x = 6/0.80 = 7.5 liters

When filling a 15-quart system with a solution that is 60% coolant and 40% water, how many quarts of coolant would be required?

Solution:

(15 quarts)(60%) = (15)(.60) = 9 quartsNeed 9 quarts of coolant

According to the following chart, if you had a 25-quart system that contained 15 quarts of antifreeze and 10 quarts water what would the boiling point of the system be?

Freeze/Boil Protection Chart*Using a 15 PSI Pressure Cap 

Protects from% of Cooling System Capacity Freezing Down to Boiling Up to *

50 �34º F 265º F60 �62º F 270º F70 �84º F 276º F

Solution:

15/25 = 3/5 = 0.60 = 60%Reading from chart: 60% = 270º F

An engine is operating at 70ºC and the coolant temperature sensor has a resistance of 3,400 Ohms.  Is this a logical temperature resistance temperature relationship?

Coolant Temperature SensorTemperature to Resistance Values (Approximate)

 

ºF ºC Ohms210 100 185

160 70 450

100 38 1,600

70 20 3,400

40 �4 7,500

20 �7 13,500

0 �18 25,000

�40 �40 100,700

 

 

 

 

 

 

Solution:

No. Reading from the chart, for 70°C, the number of Ohms should be approximately 450.

Problem:

A vehicle is getting 20 miles per gallon (mpg) with the engine operating at approximately 180°F. For each 10° increase in engine operating temperature above 160° the fuel economy will increase 2.5%. If the 180° thermostat is removed and replaced with a 200° thermostat, what will be the new mpg?

Solution:

Replacing the 180° thermostat with a 200° thermostat equals a 20° increase in operation temperature.

Therefore, 20 mpg � 2.5% (0.025) = 0.5 mpg, and20 mpg + 0.5 mpg = 20.5 mpg

Problem:

You just recently accepted a position at one of the Big 3 automakers setting up auto repair training programs at dealerships throughout the state. As part of your benefit package, you have the choice to 1) use a company car for business, 2) lease a car, or 3) get reimbursement for using your car for business travel. The specifics of each are as follows:

1. Company car: You may use a company car on business only. The company car must stay at your work location whenever not in use. You must use your own transportation to and from work. The company pays all costs (gas, maintenance, insurance and repair) of the car. Your personal car gets 26 miles per gallon and the maintenance and repair costs average out to 28 cents per mile.

2. Lease a car: You may lease a car for your business and personal use. (you will not need another car) The lease costs $350 per month of which the company pays 70%. (Your company assumes you will use the car 70% of the time on company business and the other 30% of the time will be used for personal business). The company will also pay 70% of the cost of gas, insurance, maintenance and repair of the car. The leased car averages 31 miles per gallon and the maintenance and repair costs average out to 28 cents per mile.

3. Reimbursement: The company reimbursement rate for using a personal car on company business is 37 cents per mile.

Determine the best deal for you assuming you average 1900 miles per month while on business and 1500 miles per month personal (includes commuting to/from work). Also, assume an average cost of gasoline of $1.50 per gallon and a 20 day work month.

Solution:

Determine your transportation costs for all three options.

1. Company car:No cost for the company car, however you still need a car for personal use.1500 miles � 26 miles/gal = 57.7 gal. � $1.50 gal = $86.541500 miles � $0.28/mile = $420.00Your personal cost: $86.54 + $420.00 = $506.542.

2. Leased car:You can use this car for business and personal use. $350.00 � 0.30 = $105.003400 miles � 31 miles/gal = 109.7 gal � $1.50/gal. = $164.52 � 0.30 = $49.353400 miles � $0.28/mile = $952.00 � 0.30 = $285.60Your personal cost: $105.00 + $49.35 + $285.60 = $439.95

3. Reimbursement for business use for your personal car.

Cost:3400 miles � 26 miles/gal = 130.77 gal � $1.50/gal = $196.153400 miles � $.28/mile = $952.00

Reimbursement:1900 miles x $.37/mile = $703.00Your personal cost: $196.15 + $952.00 � $703.00 = $445.15

Thus, option #2 ($439.95) is the best option for you.

Problem:

Joe is keeping a log of mileage in his new car. Complete the following chart.Mileage Miles Traveled Gallons Purchased Miles Per Gallon

720 ********** ********** **********

1080 18

1424 17

1803 16

1. Is his mileage getting better or worse?a. Betterb. Worsec. About the same

2. What is his average miles per gallon?a. about 17 mpgb. about 19 mpgc. about 21 mpgd. about 23 mpg

Solution:Mileage Miles Traveled Gallons Purchased Miles Per Gallon

720 ********** ********** **********

1080 360 18 20

1424 344 17 20.2

1803 379 16 23.7

1. a. Better

2. mpg = 

Avg = (20+20.2+23.7)/3 = 63.9/3 = 21.3 

c. About 21 mpg