Dismantle and Assemble Four Stroke Single Cylinder Petrol Engine

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VBN651 – Dismantle & Assemble Engine 4 Stroke Single Cylinder (Petrol) Page 1.

Student Learning Guide & Record

DATE INSTRUCTOR’S TASK PAGE TASK TITLE COMPLETED SIGNATURE

Assessment 1 13 Explain the term ‘configuration'

Assessment 2 13 Identify engine configurations

Assessment 3 14 Identify four stroke engine configurations

Identify and explain the following major Assessment 4 20 engine components

Assessment 5 26 Four stroke principle of operation

Assessment 6 29 Explain four stroke principle of operation

Assessment 7 33 Review questions – Lead, lag and overlap

Assessment 8 34 Explain a valve timing diagram

Assessment 9 34 Complete four stroke cycle chart

Assessment 10 42 Review questions water cooled engines

Assessment 11 45 Identify cooling system components

Identify location and function of major Assessment 12 46 cooling system components

Assessment 13 48 Identify major components

Assessment 14 48 Describe safety precautions

Review question engine lubricating Assessment 15 53 system Identify various seal types and state an Assessment 16 55 application for each

Assessment 17 59 Review questions – Gaskets

Assessment 18 59 Identify a range of gasket materials

Identify sealant types and state an Assessment 19 60 application for each

Assessment 20 64 Review questions

Assessment 21 66 Review questions

DATE INSTRUCTOR’S TASK PAGE TASK TITLE COMPLETED SIGNATURE

Dismantle, inspect, measure and Assessment 22 68 assemble a four stroke petrol engine Research engine dismantle, inspect and Assessment 23 69 reassembly procedures

Assessment 24 71 Engine specifications

Dismantle, clean, inspect, measure and Assessment 25 77 reassemble a single cylinder petrol engine

Assessment 26 77 Carry out reassembly inspection

Assessment 27 77 Rectify any faults discovered

Assessment 28 78 Write a condition report for the customer

Assessment 29 78 Evaluation

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DISMANTLE AND ASSEMBLE FOUR STROKE SINGLE CYLINDER PETROL ENGINE

INTRODUCTION The four stroke engine is in comparison to the two stroke engine more complex in construction and operation, as it has many more primary moving parts (crankshaft, connecting rod, piston, camshaft, inlet valve and exhaust valve.). There is a large variety of design and construction that may be incorporated in a four stroke engine, the engine may be small or large, operate on the four stroke principle of operation, be air or water cooled and be constructed, basically, of aluminium alloy, cast iron, or a combination of both. The engine may also be one that operates on petrol or diesel.

You need to have a thorough understanding of how a four stroke engine works before you can competently dismantle and assemble it.

Enjoy gaining the knowledge of how a four stroke engine works and look forward to the feeling you get from dismantling and assembling the engine as per manufacturer specifications.

ENGINE CONFIGURATIONS Engine configurations are usually described by the number of cylinders, arrangement of the cylinders (inline, horizontal, vee), position of the camshaft and how many camshafts.. The alignment of the crankshaft is also sometimes mentioned and can be either horizontal or vertical shaft.

The majority of four stroke engines have one to eight cylinders, although twelve and sixteen cylinders designs are not unknown.

There are several different multi cylinder layouts. The three most common designs are:

1. Inline – In the inline layout, the cylinders are arranged inline with one another.

Inline Engine Layout

2. Horizontal – Horizontal engine layout (also called flat or opposed) are arranged with the pistons set 180° apart. Horizontal Engine Layout

3. Vee – The name describes the cylinder arrangement well. The cylinders are set 90°, 60° or other variations of degrees apart.

Vee Engine Layout

Engine variations: valve layout Four stroke engines employ one of three basic valve and camshaft layouts;  Side valve  Overhead valve (OHV) and  Overhead camshaft (OHC).

Side valve The side valve layout is almost a thing of the past. One will find it on older machines and on lawn mowers. Side valve engines have a flat cylinder head that generally houses no moving parts. In a side valve layout, the valves run along the outside of the cylinder. The valves are actuated by a camshaft driven through meshed gears or chain off the crankshaft. The design is simple to manufacture, but does not produce high compression ratios or let the engine breathe easily. Side valve engine layout

Overhead valve The overhead valve layout, though more advanced than the flat head design is found on a few motor cycle engines, on lawn mowers and on small industrial engines. This design allows the valve to be located in the head, above the pistons, so that they enter the combustion chamber from the top. Push rods activate rocker arms that open the valves. An OHV layout allows for more efficient delivery of the fuel and air into the combustion chamber, but has the disadvantage of considerable reciprocating mass in pushrods, rocker arms and sometimes lifters.

Overhead valve engine layout

Overhead camshaft The overhead camshaft is the most advanced of valve design layouts. It is found on most high performance engines. The valves and the camshaft are situated above the combustion chamber. With valves and camshaft in close proximity (no more pushrods and often no lifters) the camshaft operates the valves. This layout greatly reduces reciprocating mass and allows the engine to rev higher before valve bounce occurs. This layout can employ a single cam (SOHC) or dual cams (DOHC) With SOHC , one camshaft actuates both inlet and exhaust valves. With DOHC, inlet and exhaust valves are actuated by independent camshafts. OHC designs often have three, four or even five valves Overhead camshaft engine layout per cylinder

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ASSESSMENT 1: EXPLAIN THE TERM ‘CONFIGURATION'

Explain in your own words what is meant by the term engine configuration.

......

ASSESSMENT 2: IDENTIFY ENGINE CONFIGURATIONS

As mentioned earlier, engine configurations are usually described by the number of cylinders, arrangement of the cylinders, position of the camshaft and how many camshafts.

In the following diagram, identify the four stroke engine configuration.

ENGINE CONFIGURATIONS

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150cc liquid-cooled, 4-stroke, SOHC single-cylinder, 4-valve fuel-injected engine

FOUR STROKE PRINCIPLE OF OPERATION INTRODUCTION

The majority of small engines operate on the four stroke cycle, and are known as four cycle engines. Another name for this cycle is "Otto cycle" after the name of the inventor. The "Otto cycle" is divided into four strokes, each of which, theoretically, lasts one hundred and eighty degrees of crankshaft rotation. During each stroke a definite operation is carried out in each cylinder as shown below.

The four strokes are illustrated and are named as follows:

1. Induction

2, Compression

3. power

4. Exhaust Single cylinder OHC engine

1. INDUCTION STROKE

On the intake stroke the piston and rod assembly is pulled down the cylinder by the crankshaft. During that time the inlet valve is held open by the camshaft and the exhaust valve is closed.

Since The piston has moved down the cylinder, creating a low pressure area (vacuum) atmospheric pressure forces an air-fuel mixture past the open inlet valve and into the cylinder. The air and fuel is delivered to the engine via the fuel system at a ratio of approximately 14.75:1

Atmospheric pressure is approximately 101.35 kilo/ pascals (14.7 p.s.i.) at sea level.

Pressure in the cylinder on the intake stroke is considerably less and this difference is the force that causes that air-fuel mixture to flow into the cylinder. (Liquid or gas will always flow, from high to low pressure area).

When the piston reaches the bottom of its stroke, the inlet valve is closed by the action of its spring. This stroke is called the induction Induction stroke stroke.

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ADVANCE OF SPARK, VALVE LEAD, VALVE LAG AND VALVE OVERLAP

In an actual engine valves are not opened or closed precisely at TDC and BDC. The reason is that the air-fuel mixture has mass and by virtue of this mass possesses inertia or reluctance to movement, and once having started to move has velocity and so momentum, that tends to keep it moving. The engine incorporates valve lead, lag and overlap to help overcome the inertia of the air/fuel mixture and to take advantage of the momentum of the air/fuel mixture once it is moving.

TYPICAL VALVE TIMING DIAGRAM

Such diagrams show clearly, in terms of the position of the crankshaft during its rotation and the times of opening and closing of the valves for a complete cycle.

Valve Timing Diagram

ADVANCE OF SPARK

If a combustion process is normal, the maximum pressure due to the burning gases will be applied to the piston when the crank throw has gone 5 – 10º past TDC on the power stroke. This maximum pressure will be of the order of 3500 – 7000Kpa. Combustion is rapid and rapidly increases the pressure inside the cylinder four-fold, but it does take time. From the initiation of the spark until maximum pressure is reached takes in the order of 0.0035 seconds, and this corresponds to an angular crankshaft movement of 42º at 2000 rpm. If the ignition is advanced 35º before TDC of the compression stroke, the maximum pressure at 2000 rpm will occur at 7º past TDC on the power stroke and the most effective range of angles between the crankshaft and the connecting rod will be utilised.

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GASKET MATERIAL AND SEALING COMPOUND INTRODUCTION

In an engine where machine parts fit together, gaskets and sealants are used to make the joints tight and to prevent leakage of oil, water and gas.

Gasket material and sealants are somewhat resilient, (soft and springy) and will adapt itself to expansion and contraction of the mating pats. It will also conform to irregularity in the services of the mating parts.

GASKET SEALANT Types of Sealant Gasket sealant is used instead of pre-formed gaskets between some engine mating surfaces. Two types of gasket sealant are commonly used: room temperature vulcanizing (RTV) and anaerobic. Since these two materials have different sealing properties, they cannot be used interchangeably. Care must be taken to ensure that the correct type is used for each application.

Various Types of Sealants

RTV Sealant This is a black silicone gel supplied in tubes. Moisture in the air causes RTV to cure. Always place the cap on the tube as soon as possible when using RTV. RTV has a shelf life of one year and will not cure properly when the shelf life has expired. Check the expiration date on RTV tubes before using and keep partially used tubes tightly sealed.

Applying RTV Sealant Clean all gasket residue from mating surfaces. Surfaces should be clean and free of oil and dirt. Remove all RTV gasket material from blind attaching holes, as it can cause a “hydraulic” effect and affect bolt torque.

Apply RTV sealant in a continuous bead 2-3 mm thick. Circle all mounting holes unless otherwise specified. Torque mating parts within 10 minutes after application.