Starting and Charging systems

Starting Systems

Inertia Starter: An Inertia starter is a starter motor that uses the momentum of the armeture turning to throw the pinion gear out toward the flywheel. As power is channeled to the starter the armeture starts to rotate. A worm gear within the pinion, mounted to the armeture shaft, moves the pinion outward engaging it with the flywheel as it turns. Once the pinion reaches the end of the shaft and is engaged the torque from the armeture turns the engine over.

Pre-Engage Starter: A Pre-engage starter motor is very similar to an inertia starter however instead of using inertia to throw the pinion out a small solenoid is used to engage the pinion before the armeture turns the engine over. A primary circut throws the pinion out, once the pinion has been thrown out power is feed to a second circut to hold the pinionn in place as the armeture turns.

Reduction Gear Starter: A reduction gear starter was designed to reduce size and power consumption of the starter motor. This unit incorporates a geartrain between the armeture and the driveshaft. This system permits higher speed, lower current, lighter more compact motor assembly and allows for increased torque.

Charging Systems

Alternator:

A alternator is an electromagnetic device that is driven via a belt or chain from the engine. This device is an auxillary device and will not run under its own power. Tipicaly this is a rotating magnet feild(Rotor) that turns within a stationary set of conductors(Stator).  As the rotor is driven the magnet acts on the stator producing an alternating(AC) current. This current changes due to the different polarity of each side of the magnet. This current is then feed through a rectifier which stabilises the voltage to a direct(DC) current. The alternator is used to power the electrical systems of the engine once started and charge the battery.


References
Ed May Vol 1
Ed May Vol 2
http://www.wikipedia.com/

Ignition Systems

Ignition Systems

 What substances that for electrolyte in a battery?

An Electrolyte is a substance containing free ions that make the solution electrically conductive. There are two substances that form electrolyte in an Automotive/Marine battery. An acid solution, usually sulfuric acid, mixed with water forms the electrolyte that floods round the lead inserts. As electricity is pumped into the battery it is stored within this solution.

What three elements are required to make a petrol engine run efficiently?

A four stroke and two stroke engine requires three elements to run. Air, Fuel and Spark. In the absence of any of these three components the enginne will not run. Note that a 2 stroke engine needs lubrication added to the fuel or an engine seizure will occur.

Explain the 'Kettering ignition system' and its components.

This ignition system consists of;

Battery: This is an eletricity storage device.

Ballast resistor: This is used to limit the amount of current in an electrical circut.

Ignition coil: This is a major component within the ignition system. It consist of a primary winding wraping around a more concerntrated secondary winding. This device is used to boost the current from the battery to ingnite the fuel.

Distributor: Once the high energy charge has left the coil it is transfered to the distributor, this unit the distributes the spark between the sparkplugs using the rotor within it.

Capacitor: This is a small unit designed to stop the charge from the coil jumping the gap between the points as the voltage increases.

Points breaker: The points are where the connection between the coil and the spark plugs is connected and disconnected.

High-tennsion leads: These leads are used to transfer the high voltage from the distributor to the spark plugs.

Spark plug:  This is the final comonent in the ignition system. The spark plug uses a high energy current to arch across its self igniting the fuel.

Electricity is feed through the ballast resistor to the Ignition coil. Current flows into the coil charging up the primary windings, as the distributor points are open (A capacitor within the distributor stops the coil from arching across the point gap). As the distributor rotates and the points close, the primary coil is collapsed into the secondary winding (consisting of several thousand turns of a very fine wire) boosting the voltage to 30-40 thousannd volts. The secondary winding is then channeled through the distrubutor points, rotor, high-tension leads to the spark plugs.

Explain 'Dwell angle' in a distributor.

The Dwell angle refers to the length of time the points are closed on a distributor. This is measured by degrees of rotation on the distributor shaft. Generally the manufacturer will recommend a dwell angle of 54 degrees.

Why is the heat range of a spark plug important?

The heat range is important for a number of reasons. If the tip of the spark plug gets too hot it can cause problems such as pre-ignition or detonation. If the tip of the plug is too cold then deposits can form on the insulator reducing spark current or shorting the spark plug.

What is a 'Capacitor discharge' ignition system and how does it work?

This sytem is different from the conventional kettering system. Consisting of a transformer, charging circut, rectifier, capacitor, coil and spark plug. Voltge is raised by the small transformer to betweenn 400-600volts annd then transfered to the charging circut to charge the capacitor. A rectifier in the charging circut is used to ensure the capacitor does not discharge before the moment of ignition. When sensors determine ignition timing the charging system is cut allowing the capacitor to discharge into the coil. This then raises the voltage again discharging up to 40,000volts out through the spark plug.

Referrences

Ed May Vol 1

Ed May Vol 2

http://www.wikipedia.com/

Marine Buisness Practise

Marine Buisness Practise

Warrentees- A warrentee is given to a piece of equipment such as an outboard engine. A warrantee is a legal assurance that an item will perform the task it is built for. This assurance does come with some conditions and it is important that you make sure you read the warranntee and adhere to these or the warrantee with be void. For example when you buy a new outboard engine there are certain proceedures that must be done when starting and running the engine for the first time. Such as using a type of oil or not exceedinng a certain number of revs.

Guarantees- A garrantee is an assurance of workmanship. When a part is repaired for example, you give your assurance that this part will perform its job. Should this part fail you are responsible and are expected to cover the repair cost. If this part had been replaced with a new part then it would be covered by a warrantee.

Quotations- When giving a quote it is important to remember that this is a fixed price. Taking into account all that may be needed for a job such as parts, consumables, labour. If something should not be foreseen such as extra parts or labour it is now up to the person who delivered the quotation to cover the extra cost.

Estimations- Unlike a quotation, an estimation gives you room to move. It is effectively a guess. Parts, consumables, labour are all taken into account and a price is given for the job. However this price is not fixed and should unforseen circumstances arise, this is discussed with the customer.

Charge out rates- When choosing your charge out rate it is important to take into account all your expenses. For example when working in a workshop the rate you pay, e.g $60/hr, will include three divisions. Usually along the lines of $20/hr paid the the employee, $20/hr for the owner and $20/hr to pay for overheads. Overheads such as Rent, Power, Rates, Upgrading equipment.

Courtesy services- This is the services that are offer by a buisness that are not necessary but are done out of courtesy. Such as courtesy cars, dropping off or picking up a customer, checking tyre pressures, washing a car after work is done etc

Cultural issues- Cultural issues reffer to differences between cultures such as expectations, Practises, Communication issues etc.

Marine Transmission

Marine Transmissions

Gear selection systems

Outboard gear cases - An out board gearcase uses a 'Dog clutch' system. this is a double sided engaging gear. The dog clutch is mounted to the propellor shaft with the ability to slide. The selector rod pushes the dog clutch fowards or backwards to engage the propellor shaft to the driven gears.

Stern drive - Unlike an outboard the gear selector system is in the top of a stern leg, and sits vertical instead of horizontal. In this system a selector arm pushes a tapered cone, often made of brass, up or down the driveshaft to engage the foward or reverse gear. This system works similar to a baulk ring in an automotive gearbox and uses friction to engage the gear.

Inboard gearbox - Inboard gearboxes use a hydrolic clutch type engagemet system similar to a motorbike clutch. The selector changes the flow of fluid to each clutch unit within the gearbox as pressure builds the clutch plates engage the desired gear.

What type of gears are used in Outboards & Sternlegs?

Helical cut, constant mesh, gears are used in both outboard gearcases and sternlegs. This type of gear is used because having and helical cut gear provides more contact area between gears and reduces noise. Having a constant mesh gear system also reduces moving parts reducing possible problems. These gears are then engaged to the propellor shaft via an engagement system such as a dog clutch.

Duo Propellor systems

Invented by Volvo Penta this system consists of two propellors rotating in opposite directions. The main propellor is mounted to the main shaft with a second shaft mounted through its center. A second propellor is mounted to the second shaft and spins in the oposite direction. This system in designed to reduce cavitation, vibrations and increase power and handling.

'V' drive systems
A v drive system is used instead of a standard shaft drive system when there is little space to work with. This system allows the drive line to move around tight angles or change direction as in this diagram.

 

Jet Unit or Surface drive?

Jet unit - A jet unit is like an internal propellor. Water floods through the intake as the propellor turns which inturn blows out the rear of the boat under pressure. This system is good for conditions such as shallow waterways.

Surface drive -  A surface drive unit operates with the propellors half inn half out of the water. This type of system is used because it reduces drag therfore allowing for increased speed and lower fuel comsuption.

Both systems have their own advantages however I would lean more the Jet unit as this would be suitable for both shallow and deep water. This unit also has the added safety of not having exposed moving parts, but retains power and control. 

Engine Reflection

Engine Reflection

Cylinder Head

An inspection of a cylinder head begins with a visual examination, searching for signs associated with wear e.g warping, cracks, chips, deformation etc, followed by a number of measuring tasks to determine wear tolerances.

Cylinder Head Warpage is measured using a straight edge and a feeler gauge. The straight edge is held against the machined surface and a feeler gauge is fitted were possible. If a measurement is able to be taken this measurment is compared with manufacturers tolerances. If warpage is too great then the surface will need to be machined again.

Valve guides are checked by feeling for play with the valve in place. Measurements are taken of the bore, two measurements 90' of each other, at three places down the valve guide bore. These measurements are used to determine Taper and Ovality within the guide.

Valve Stems are visualy checked (Stretching, bending, erosion, wear marks) as well as measured. These are measured using the same process as when measuring the guide bore.

Stem to Guide clearance is measured by comparing the two previous measurements. Subtract the valve stem width from the guide measurements and you will be left with the stem to guide clearance.

Valve seats are measured for angle, width and finish. These measurements are compared with manufacturers specifications and if need, reseated.

Valve spring squareness is measured using a surface plate and engineers square. A feeler gauge is used to measure how far off sqaure the spring is. This measurement is compared with manufacturers tolerances and replaced if need be. If a spring is not square this is a sign of wear.

Valve spring Length measured using a vernier. A set of valve springs should be within 1.5mm of each other. If this is not the case then the whole set should be replaced. 

Valve spring installed height is the measurement taken from the spring seat to the retainer. This is done without the spring in place. Remeber to account for the VSI(Valve spring insert). This measurement is used with a spring pressure tester to determine spring tension.

Spring Tension. When using a spring pressure tester the spring is put in place and would down untill it is the same length as when installed (Spring installed height). As the spring is wound down it pushes in the base plate giving a pressure reading. Spring tension can be increased or decreased by adding VSI however remember that ther must always be 1 VSI per spring. All springs should be within 5kg of each other.

Good Practise is to check all nuts, stud, bolts, threads as you work and replace or recondition where needed.

Frost plugs should also be checked for leaking, deformation and corrosion.

Cam Lobes are measured to determine the lift of each lobe. The are measured at the widest point and the narrowest point(where the wear begins). This measurement allows us to work out how much travell the valve will have and when it start to open and close.

Bearing Journals are also measured. From these mesurement we can determine Taper and Ovality.

Runout of the crankshaft is measured usind a DTI gauge(Dail test indicator) and a mircometer. A measurement is taken usinng a DTI gauge then converted to a metric reading using a mircometer. This measurement is then compared with manufacturers tolerances.




Plasti-gauge is used to measure oil clearances in various parts of the engine. For example when measuring the oil clearance of a crank/cam journal a slither of plasti is placed in the journal and then as the bearing cap is tightened it squashes down. Once the cap is removed the thickness of the plasti-gauge is measured to determine clearance.

Short block & Outboard

The Piston is measured along its thrust sides. Aprox 10-15mm from bottom of skirt. This measurement is done with a micrometer and then compared to mannufacturers specs to determine if/how much wear has occured. A visual inspection is also done.

Cylinder Bore is measured the same was as the valve guide, however a bore gauge is used. This measurement will allow us to calculate Taper and Ovality of the bore.

Piston to Bore clearance is determined using measuremennts of the piston and bore. Subtract the width of the piston from the bore and this will give you the clearance.

Piston ring side clearance is measured using a feeler gauge placed just above the ring while in place. This is measured to ensure that the ring has enough clearance after the ring has expanded due to heat. The measurement is then compared with manufacturers specifications.

Piston ring end gap is also measured to ensure clearance upon thermal expansion. The ring is placed within the bore and using a feeler gauge a measuremnnt is taken, thenn compared to manufacturers specification.

Connecting rods are measured for bend and twist. This is done using an engineers square and a feeler guage. if deformation is minor then the rod may be rectified rather than replaced.

Note: Some manufacturers recomend replacement rather than repair.

Note: If diagonal wear marks are present down the piston this could be a sign of a deformed Con Rod.

Main bearing & Big end journals, as with Cam journals, are measured using a micrometer. Multiple measurements are taken of each journal to determine Taper and Ovality. Measurements are compared with manufacturers specification to determine wether replacement is needed.

Crankshaft Deflection/Run out is measured usinng the same tools and processes as when measuring Cam shaft runout.

Cylinder block face is checked for warpage, erosion, cracks, corrosion. Using a stright edge and a feeler gauge the cylinder block face is measured like the cylinder head face.

Timing gear such as belts, chains, gears, sprockets are all checked for damage annd wear.

Water pumps are checked for corrosion, damage, leakage and flow rate.

Oil pumps clearances are measured using a feeler gauge and the reading is then compared to manufacturers specifications to determine condition. Gears are check for damage and wear.

This excersize of dismantling, measuring and reassembling an outboard, short block, 2-stroke and cylinder head has given me practical and measuring experience. Although there is alot of measuring involved a big part of this process is visual and I feel this excersize has given me the ability to identify wear and damage.

Gearbox Reflection

Gearbox Reflection

The past few weeks have seen us dismantling, assesing and reassembling automotive and marine transmissions. We have covered a variety of transmissions; Toyota 4k manual gearbox, Outboard gearbox, Sturn drive and hydrolic marine gearbox.

Penta Hydrolic Gearbox

During this excersize I gained first hand experience with gearboxes. I feel it is alot easier to understand how the gearbox works when your able to see how the parts move within the box. It also helped illistrate the importance of following a dismantling proccedure and during reassembly, the importance of fitting each part correctly.

Visual inspection is a major part of gearbox reconditioning, this excersize has taught me how to identify damage and wear. For example we check the case hardening on all gearbox components, if the hardened surface has any nicks or chips then this part is destined to fail. Gears are checked for wear, damaged teeth and excess play. Bearings are also checked, it is important to ensure that all bearings are running on hardened surfaces.

                       

The synchromesh unit is very important. Ensure all parts are present and check for damage and wear. It is importannt that the baulk ring in correctly fitted or it will not synchronise the gear speeds.

 Runout is measured on all shafts. Housings are measure for distortion. Oil pump clearances are checked agaist specifications. The bevel gear that drives the propellor is set to ensure correct contact.

I also learnt how to calculate a gear ratio.

Most important when dismantling an automotive gearbox... Dont loose the tic tac's!!!