Car Maintenance Basics

Chapter 1 Project 1 Basics of Vehicle Maintenance Technology ([-])
Automobile is a high-value mechanical product. During long-term use, with the increase of driving mileage, its technical status will continue to change, its performance will gradually deteriorate, and failures and damages will inevitably occur.Therefore, it is of positive significance to prevent the occurrence of failures by taking corresponding maintenance measures according to its changing law and performing maintenance and repairs according to the situation.

Technical requirements and safety rules for task [-] vehicle maintenance
Knowledge goal:

Know the technical requirements for car maintenance.

Master the safety rules of auto repair companies.

Master the safety operation procedures of automobile maintenance enterprises.

Skill Goal:
The battery will be charged.

Be able to operate the safety equipment of an auto repair business.

task description
Under the guidance of teachers, learn the basic technical requirements of automobile maintenance and master the safety rules of automobile maintenance enterprises.Under the guidance of the work order task, complete the study of the technical requirements and specifications of automobile maintenance, and carry out safe operation of fire-fighting equipment, charging equipment, electrical equipment, lifts, etc. in automobile maintenance enterprises.Record and archive the completed work, consciously maintain safe operation and 5S work requirements.

Group related knowledge
[-]. Technical requirements for vehicle maintenance

The process of car maintenance includes steps such as disassembly, cleaning, inspection, assembly and adjustment, and each step has its specific requirements.

1. Requirements for car disassembly

①Before the car is disassembled, first understand the technical data of the model, master the assembly relationship and technical requirements of each component.

② When disassembling the assembly or parts, it should be carried out in order, and the parts with tolerance fit and parts that should not be interchanged should be inspected and marked with assembly marks.Such as valves, connecting rods and bearings, left and right housings of differentials, plunger couplings, etc.

③ When disassembling parts with adjusting shims, do not lose or damage the shims, such as the adjusting shims of the final reducer, the adjusting shims of the bearing tightness of the steering gear, etc.

④ When dismantling the rusted parts, it can be decomposed after being soaked in kerosene or gasoline, loosening agent or heated. Do not knock hard to avoid damage to the parts or tools.

⑤The disassembled bolts and nuts can be put back in place without affecting the performance.

⑥ When disassembling, for the convenience of cleaning, the parts suitable for different cleaning methods are classified and placed, such as steel parts, aluminum alloy parts, rubber parts, leather parts and friction plates.

⑦ When disassembling, it is necessary to ensure that the lubricating oil, tools and parts do not fall to the ground.

⑧When disassembling, the parts should be arranged according to the assembly relationship as much as possible to facilitate assembly.

⑨ When disassembling, the precautions for using tools are as follows:
a. Screwdrivers and pliers are not allowed to be used instead of hammers and blunderbusses. Attention should be paid to the magnitude and direction of the force on the tools.

b. When disassembling, reasonable tools should be selected according to different parts, and should not be replaced by force.

c. When disassembling shafts, pins, bushings and other parts, use copper rods to pad them, and never hit them directly, so as not to deform and cause assembly difficulties.

d. When disassembling gears and bearings, pullers or pressure tools should be used for disassembly.

2. Requirements for auto parts cleaning

After the car is used, dust, oil, scale, old paint and rust will inevitably stick to the surface of the parts.In order to facilitate inspection and repair, the dirt must be completely removed.

(1) Remove carbon deposits
Mechanical and chemical methods can be used to remove carbon deposits.

①Mechanical method.Use a special wire brush installed on the electric drill for scrubbing, or scrape off with a scraper or spatula.

② chemical method.Use chemical solvents to have chemical and physical interactions with the carbon layer to soften the carbon layer.When cleaning, the temperature of the solution should be kept at 80-90°C. After soaking and softening the carbon deposit, wipe it clean with a brush or cotton gauze.After removing carbon deposits, if it is aluminum alloy, the parts should also be washed with hot water.The solvent formula for chemical carbon removal is shown in Table 1-1.

(2) Removal of oil stains
①Cleaning of metal parts.Oil cleaning of metal parts can be done by cold washing or hot washing.

a. Cold wash method.Use diesel oil, gasoline or kerosene as cleaning agent, and blow dry with compressed air after cleaning.This cleaning method is simple, convenient and fast; but it is not safe and the cost is higher.

b. Hot washing method.Using alkaline solution as a cleaning agent has the same effect as oil washing, but at a lower cost.The solvent formula is shown in Table 1-2.

The heating temperature of alkaline solution is generally 70-90°C.Heating can accelerate the flow of the solution and reduce the viscosity of the oil film, and accelerate the degreasing.If the solution can be stirred, it will accelerate the separation of oil stains from the metal surface, thereby accelerating the cleaning process.

Under normal circumstances, put the parts into the alkaline solution for 10-15 minutes, then take it out and rinse the alkaline solution with clean water, and then dry it with compressed air.

② Cleaning of non-metallic parts.Cleaning of rubber parts, such as brake cups, aprons, etc., can be cleaned with alcohol or brake fluid instead of gasoline or alkali solution to prevent parts from swelling and deterioration; leather parts should be washed with soap water first, and then Rinse with clean water, and finally dry with a dry cloth; the clutch and brake shoe friction plates are generally scrubbed with a little gasoline.

3. Inspection and classification of parts
The inspection of parts is one of the important tasks in the process of automobile maintenance.Through the inspection of the parts, find out the technical status of the parts and determine the maintenance plan.Therefore, it has a decisive impact on the repair quality, material consumption, work efficiency and repair cost of the car.The basic methods of parts inspection include empirical method, measurement method and detection method.

⑴ Empirical method
The empirical method is a method of inspecting and judging the technical status of parts through observation, tapping and comparison.This method is simple and easy, but requires the repairman to have experience with the fit clearance, torque size and sound.This method is more effective for more obvious defects, but it is difficult to accurately judge complex faults.Therefore, it is used as an auxiliary inspection method during car maintenance.Empirical methods include appearance inspection, hand feeling method, percussion method and comparison method.

① Appearance inspection.A method of visually inspecting roughness, grooves, scratches, peeling, cracks, defects, deformation, wear, etc. on the surface of parts.

② feel method.A method of checking the clearance of mating parts by hand shaking or twisting.Such as shaft and bearing fit.

③ Percussion method.The percussion method is to use the sound produced by percussion parts to check the technical condition of the parts, mainly to check for cracks and loose connections.If there is a crisp sound, it means that there is no crack or the connection is tight; if the sound is hoarse, it can be determined that the part has cracks or the connection is loose.

④ comparative method.The comparison method is a method of checking the technical status of parts by comparing old and new parts.Such as the length of the spring, the elastic strength, the quality of the rolling bearing, etc.

(2) Measurement method

The measurement method is a method of using measuring tools and instruments to measure and inspect the technical status of parts.It is the most important inspection method in the process of car maintenance.Using measuring tools and instruments to inspect parts can obtain more accurate data and provide a reliable basis for the maintenance of parts.

(3) detection method

Detection method is an inspection method for hidden defects of parts.For example, the inspection of fine cracks in important parts such as crankshafts and steering knuckles.There are two methods of oil immersion hammer inspection and magnetic flaw detection inspection commonly used in automobile maintenance.

①Immersion hammer test.When inspecting, first immerse the parts in kerosene or diesel oil for a while, take them out, wipe the surface dry, sprinkle a layer of white powder, and then lightly tap the non-working surface of the parts with a small hammer.If there are cracks in the part, the kerosene (diesel oil) soaked into the crack due to vibration seeps out, making the white powder at the crack appear as a yellow line mark.Determine the crack location based on the line marks.

②Magnetic flaw detection inspection.Magnetic flaw detection inspection is to use a magnetic flaw detector (Figure 1-1) to magnetize the part, so that the magnetic force line passes through the tested part. If there is a crack on the surface, the magnetic force line will shift or be interrupted at the crack site to form a magnetic pole and establish its own magnetic field.If fine-grained iron powder is sprinkled on the surface of the part, the iron powder will be magnetized and attached to the crack, thus revealing the location and size of the crack.When performing magnetic flaw detection, the magnetic force lines must pass through the crack vertically, otherwise the crack will not be found.

(4) Classification of parts

After the parts are inspected, they are divided into three categories: usable, to be repaired, and scrapped.

①Usable parts.A serviceable part is a part that meets the requirements of the overhaul technical standard and can continue to be used without repair.

② Parts to be repaired.Parts to be repaired are parts that can meet the technical standards for overhaul after repair.

③Scrap parts.Scrap parts are parts that are damaged beyond repair or have no repair value.

4. Requirements for car assembly

①All parts must be thoroughly cleaned and blown with compressed air before assembly, and can only be assembled after passing the inspection.

②The burrs, bumps or hammering scars on the surface of all machined parts must be filed and repaired if they affect the assembly quality.

③ If the internal and external threads of the parts are broken, deformed or slipped beyond the effective range of more than two threads and cannot be repaired, they cannot be assembled.

④ All bolts (nuts) with specified tightening sequence and torque requirements must be tightened according to the specified sequence and torque.

⑤ All flat washers, spring washers, cotter pins, safety locks, etc. used for bolted connections must be fully assembled in accordance with regulations.

⑥ When assembling shafts, pins, bushings and other parts, they can be hammered with copper rods, and must not be hammered directly.

⑦ For the bolts and double screws in the cylinder head, cylinder water channel side cover, intake and exhaust manifold, carburetor and water pump, etc., apply red lead oil to the threads before installation.

⑧ All leather oil seals should be immersed in a mixture of 60°C (engine oil and kerosene account for 50% each) for 5-8 minutes before installation.If it is a colloidal oil seal, apply gear oil to the friction part.When installing, the outer circumference of the iron shell and the seat ring of the oil seal should be painted with zinc white paint.

⑨When replacing the friction plate or brake band of the automatic transmission, the new friction plate or brake band should be soaked in clean ATF for 15 minutes before installation.

⑩All oil nipples and oil cups should be fully assembled, and lubricating oil (grease) should be added according to the season (time) and type, and the mutual moving surfaces should be coated with lubricating oil (grease).

[-]. Safety rules for car maintenance
Carrying out the safety rules of car maintenance is a measure to prevent accidents caused in the process of car maintenance, so every repairman is required to strictly abide by them.

1. Safety rules for using gasoline

① Fireproof and explosion-proof.Gasoline is flammable and explosive. It can ignite when it comes into contact with tiny sparks. When using it, pay attention to fire prevention and explosion protection.In the repair shop and maintenance place, it must be well ventilated to avoid fire caused by excessive concentration of gasoline vapor.It is strictly forbidden to disassemble the fuel tank that has been filled with gasoline by means of gas cutting to avoid explosion.

②Prevent poisoning.Ethyl gasoline (containing tetraethyl lead) is poisonous, and it will cause poisoning if it touches the damaged skin or inhales it into the human body.Therefore, ethyl gasoline is colored red or orange to distinguish it.All workers who have been exposed to ethyl gasoline must wash their hands with soap to avoid poisoning when eating or smoking.

2. Safety rules when starting the engine

① Before starting the engine, first check the engine oil, the coolant in the radiator, and whether the shift lever is in the neutral position, tighten the hand brake, and wedge the front and rear wheels with triangular wood.

② When starting the engine with the hand crank, it should be lifted from the bottom up on one side of the hand crank to prevent the reverse rotation from hurting people.

③When debugging the engine indoors, keep the air in the room unobstructed, and it is best to connect the exhaust pipe to the outside.

④ After the engine starts, the working condition of the instrument should be observed in time.When debugging and checking, pay attention to safety to prevent being injured by the fan and pinched by the belt.

3. Safety rules for working under the car

①When performing maintenance work under the vehicle, hang a warning sign "Do not start the engine" on obvious places such as the door or steering wheel, wedge the front and rear wheels with triangular wood, and tighten the hand brake.

②Before jacking up the car with a jack, the rest of the wheels should be wedged with triangular wood.The jack should be placed steadily and firmly, and the jack cannot be cushioned with bricks, stones or objects that are easily broken and sliding.For cars whose wheels have been jacked up and removed, when working under the car, the frame should be supported by a card stool to ensure safe operation.

③ When lowering the wheel raised by the jack, unscrew the jack switch slowly and steadily to prevent injury.

④ When working under the vehicle, do not lie directly on the ground, and try to use a sleeping board.

⑤ During the assembly operation, it is not allowed to use incorrect operation methods.For example, try out screw holes, keyholes, etc. by hand to avoid crushing your fingers.

⑥ When starting the car, it is forbidden to work under the car.

4. Safety rules for battery use
③ When preparing the electrolyte, glass or ceramic containers should be used, and the sulfuric acid battery should be slowly poured into distilled water.It is absolutely forbidden to pour distilled water into sulfuric acid, in case the temperature of the distilled water rises sharply and a large amount of steam is emitted, causing the sulfuric acid to splash and burn the skin or clothing.

task implementation
In the process of task implementation, they will learn the operating procedures and maintenance methods of safety equipment commonly used in automobile maintenance companies, and implement them in groups to complete the work within the specified time.

Tip: Before implementing the homework, each group should prepare the materials and tools needed for this learning task according to the table below.

[-]. Tool preparation

[-]. Technical requirements and standards
① All operations comply with safety technical standards.

② All operations conform to the technical requirements of automobile maintenance.

③ Safety accidents are not allowed during the operation.

[-]. The work to be done

① When moving the battery, handle it with care and do not tilt it, so as not to splash the electrolyte on the skin or clothes and burn the skin or clothes.If accidentally splashed on skin or clothing, rinse with water immediately.

② It is forbidden to put oil containers and various metal objects on the battery cover.

How to use dry powder fire extinguisher
Scope of application: It is suitable for fighting fires of various flammable and combustible liquids and flammable and combustible gases, as well as fires of electrical equipment.

① Hold the pressure handle with your right hand and the bottom of the fire extinguisher with your left hand, and gently remove the fire extinguisher.

②Remove the lead seal.

③ Pull out the safety pin.

④Hold the nozzle with your left hand and the pressure handle with your right hand.

⑤ At a distance of two meters from the flame, press down on the pressure handle firmly with your right hand, and swing the nozzle with your left hand to cover the entire combustion area.

2. Battery charging

①Clean the dirt on the outside of the battery and the oxides on the pole, unblock the ventilation holes and unscrew the cap of the filling hole.

②Connect the positive and negative poles of the charger to the positive and negative poles of the battery, ready for charging.

③ Supplementary charging often adopts the improved constant current charging method, and the steps are as follows:
a. Check the liquid level of the electrolyte, if it is insufficient, add distilled water.

b. Select the charging current to be 1/10 of the rated capacity of the battery, and charge it to a single cell voltage.

c. The charging current is halved, which is 1/20 of the rated capacity of the battery, and charged to a single cell voltage.

3. Precautions for experiment
① Do not add tap water, well water, river water, etc. to the battery instead of distilled water.

② After the battery is discharged with high current and distilled water is added, the relative density should not be measured immediately.

③When charging, there is explosive gas on the upper part of the battery. Do not smoke, use open flames or make sparks nearby.

4. Complete the training report
learning assessment
[-]. Self-evaluation

1. Summarize what are the safety measures of auto maintenance enterprises?
3. Self-evaluation of the learning environment (including dress, learning attitude, mastery of knowledge and skills, completion of work pages, etc.).

task description
Under the guidance of relevant knowledge points, understand the types of auto mechanical parts maintenance, and master the methods of auto mechanical parts maintenance.Under the guidance of the work order task, complete the operation of the technical requirements and specifications of automobile maintenance, and carry out safe operation of the maintenance equipment of automobile mechanical parts.Record and archive the completed work, consciously maintain safe operation and 5S work requirements.

related information
Auto parts will be worn, cracked, broken and deformed during use, and mechanical processing, pressure processing, electroplating processing, metal spraying processing, welding and bonding processing can be used for repairing.The repair of parts should choose a reasonable repair method according to the material, working conditions, and degree of damage of the parts to restore the technical state of the parts.

[-]. Machining repair method
The mechanical processing repair method is to restore the correct geometric shape and matching characteristics of the parts through mechanical processing methods such as turning, planing, reaming, milling, boring, and grinding.The commonly used process methods for machining repair include repair size method, additional parts repair method, partial parts replacement repair method, flipping or turning repair method.

1. Repair size method

The repair size method is to remove the surface layer of the part by mechanical processing, so that the part has the specified geometric shape and new size.It is suitable for both the expansion of the aperture and the reduction of the shaft diameter.For example cylinder (Fig. 1-5), crankshaft (Fig. 1-7) etc. are in work, often not wear evenly, but grind into ellipse and cone.In this case, the repair size method can be used to repair the cylinder, that is, when repairing the cylinder, first expand the cylinder boring and grinding to a certain level of repair size, and then replace the correspondingly enlarged piston (Figure 1-6).Another example is when repairing the crankshaft, the crank neck can be reduced to a certain level of repair size first, and then the reduced size bearing can be selected to restore the normal fit clearance.

When using the repair size method, the more expensive one of the two matching parts should be retained, the repair size should be specified, and the other part should be replaced.For example, when the cylinder and piston are repaired, repair the cylinder and match it with a piston of the corresponding size.When the crankshaft journal and the main bearing are repaired, the crankshaft journal should be repaired, and then the bearing of the corresponding size should be equipped.

Repair dimensions are usually set by the car or manufacturer.It is based on the strength of each part, the depth of the surface carburized layer or quenched layer, to specify the size of the last level of treatment.Some parts have only one repair size, and some parts have several repair sizes.The main advantages of the repair size method are: it can prolong the service life of complex and expensive parts, the processing method is relatively simple, and the repair quality is high.Its disadvantage is: too many repair sizes limit the types of spare parts, which brings great difficulties to the selection of spare parts.

2. Additional parts repair method

The repair method of additional parts is that when the shaft and hole are worn too much or processed to the last level of repair size, they can be processed to a larger size under the condition that the part mechanics allows, and a sleeve or bushing is inserted and fixed, and then Method of machining to standard size.

There must be a certain interference between the bushing and the repaired part, so that the two can be tightly connected to meet the requirements of heat transfer and force transmission, and can also be combined by screw thread and welding.

3. Partial replacement repair method
The local replacement repair method is a method for repairing parts with excessive local wear or local damage.When repairing, repair the damaged part by machining, and then use methods such as inlay welding to restore its original size and performance.This method can repair gears, splines, etc.

4. Flip or turn repair method
(End of this chapter)