Batteries

Battery is for starting the car and running accessories while the engine isn’t running. Most automotive batteries have 6 cells made of plates sitting in sulphuric acid and distilled water. This mixture is called electrolyte. Voltage is created through the chemical reaction of the lead and sulphuric acid.  A fully charged battery is 12.6V.

 When testing the battery on-car, we found water on the top of the battery casing; this could mean the alternator is overcharging. When tested the OCV (open circuit voltage) with a volt meter, it read 13V with the engine off. This indicates there is a surface charge.  This can be removed by running accessories for a few minutes. Engine running with accessories on (headlights, blower) battery was charging well and there seemed to be no descrepences.

A high rate discharge test can be performed with a carbon pile tester to find the batteries capacity and determine whether the battery is in good condition. For this test we had to find the CCA (Cold Cranking Ampere) of the battery and halve it. This is the load to use with the tester.  Connect the clamps of the tester to the terminals of the battery and turn the load dial up to half the CCA, if the voltage of the battery drops below 9.5V then a new battery is required.

Starter motors

A starter motor is used to turn the engine over. When cars first came out this would be done by hand. A ‘crank handle’ would slot into the crank and you would turn the engine over yourself. Then inertia starter motors came out. This type of starter motor uses a spiral mechanism to engage into the ring gear while pinion gear was already spinning. Problem with this is that if starter didn’t receive enough power, it wouldn’t spin the pinion gear fast enough. Resulting in gears crunching and worn ring gear over a short period. Another type of starter motor is gear reduction. These are often used in higher compression engines due to the added load on the starter. They work similar to a pre engaged starter but consist of more gears. These added gears provide a higher torque from starter.  In today’s cars the most popular type of starter motor is pre engaged. This type of starter motor engages into the ring gear before spinning. It does this with the use of a solenoid. Pull in windings activate a plunger which pushes the pinion gear into the ring gear. When the plunger is all the way in the pull in winding power down and hold in windings activate. While this is happening the plunger has connected two contacts together enabling a high flow of electricity to flow to the windings and the armature.

The starter motors principal is to turn electrical energy into mechanical energy. It does this with the use of electro-magnetism.  Because the iron core is surrounded by windings, when the electromagnetic fields cut across each other an electric current is created and absorbed into the windings. The brushes on that push onto the commutator allow electricity to pass through armature. Because the commutator is split into sections it turns windings on and off.  It is this action of turning them on and off that cause the armature to spin.

Alternators

To diagnose any problems with the charging system on a vehicle, you must first take the OCV of the battery and perform a CCA test on the battery. You do this because  if the battery isn't holding enough charge then the fault may not be the chargeing system. If under load the battery cannot hold a voltage reading of 9.5 then it is a fail. It must be charged to continue the test.


 If battery is fine, perform a visual check of wiring and connections. If any loose connections tighten them. Then you perform a voltage drop test across the wiring. A high result means that there is added resistance in the wire, which is drawing voltage away from the battery.

I learnt how to check the charging system for faults and how to diagnose certain problems.

4842 Automotive Engines questions 3

1.What is the firing order of a four stroke engine?
2.What is the difference between a S.I and C.I engine?
3.Is there any difference between a S.I and C.I piston if so what?
4.What year was the diesel engine invented and by whom?
5.What is the purpose of the oil jet on the connectng rod, and where does it spray?
6.On the connecting rod where is the big end and little end?
7.What is the purpose of the thrush washers on the crankshaft?
8.On a diesel engine whats the difference between direct injection and a indirect injection type?
9.Explan the term valve timming?
10.Why do we have valve clearance?




1. Basically 1342 but, each engine has a different firing order. But on the twin cam mazda engines we are working on when the 1st cylinder is at TDC the 2nd and 3rd are at BDC and the 4th is at TDC. So when the 1st cylinder is travelling upward toward TDC it is on the compression stroke while the 4th cylinder that is travelling toward tdc is exhausting. Mean while the 2nd cylinder is on a power stroke the 3rd cylinder is on intake.

2. Spark ignition engines use spark plugs to ignite the fuel where as a compression ignition engine relies on the high compression to ignite the fuel.


3. The pistons in a C.I engine are shaped alot differently to the S.I engine. Their piston crowns are are shaped differently due to the fact that these engines rely on compression. Also the compression engine pistons are made stronger due to being under higher stresses. 

4. The diesel engine, well the C.I. engine was invented by Herbert Ackroyd-Stuart in 1890.

5. The oil jet on the con rod sprays oil into the cylinder while the piston is travelling toward TDC. It does this because there is alot of friction created in the cylinder. So the oil is used as a lubricant to keep friction to a minimum.

6. On the conrod the big end is connected to the crankshaft and the little end is connected to the piston via the gudgeon pin.

7. The thrust bearing stops the end play in the crankshaft. Because the engine is turning clockwise it automatically forced the crankshaft forward. so the 'spacers' stop the play.

8.

TTEC 4843 automotive engines (2)

What is taper and ovality in the bore, how is it caused how do you check it?
What is side clearance on a piston and how is it checked? 
How can you tell the difference between a inlet and exhaust vavle and why?
What sort of tempatures do the inlet and exhaust valves get upto?
What temperatures and speeds must the piston be able to cope with?
Why do we have piston ring end gap clearance ?
What could the result be if the piston ring end gap is too small?
Why do aluminum cylinder heads usually have a steel shim (washer) between the valve spring and the cylinder head surface ?
What is meant by the terms S.I and C.I in a four stroke engine?
7/4/11 What is the purpose of the margin on the valve


The taper and ovality of the bore is the curvature of the bore and how worn the cylinder is from wear and tear. To check these you take dimensions of the bore. To do this you take dimensions across 'A' and 'B' of the bore. you repeat this 3 times at the top, middle and bottom of the bore. To check ovality subtract 'A' measurement form 'B'. To work out the taper of the bore subtract the measurements you took from the top of the bore from the ones you took from the bottom. 

The side clearance on a piston is gap between the piston ring and the ring groove on the piston. To check this gap you need feeler gauge. Use the feeler gauge on a smaller dimension and slip it in between the groove and ring. Continue to try this with bigger gauges until you cant fit one in and record the size you fit last.

The difference between the exhaust and inlet valves are the size. The inlet valves are generally bigger. This is because when the inlet and exhaust valves are open together bad things could happen. The fresh mixture and air may enter through the inlet valve and simply exit through the exhaust valve. The cylinder will be unfilled and produces a gas called Carbon-monoxide (Co1). This is a very harmful gas and may be fatal to your health if dose is high enough. The piston crown is generally at normal operating temp of 300 Degrees but is brought down with use of coolant. An interesting note is that forced induction engines have a operating temp of 600 Degrees at the piston crown.

The ring end gap is very important for the operation of the piston. As with all metals the ring expands when it gets hot. So the gap left at the end of the ring is to allow for the expansion of the ring. If this gap wasn't left as the ring expands it would have no where to go and distort and buckle and may cause seizure of the piston. 

We use a steel shim between the valve spring and aluminium head as aluminium is a soft metal. When under heat and higher tension the spring may cause galling on the head. The steel shim prevents this added wear on the head as it is a harder metal and the bigger surface area on the head spreads the pressure.

On a slightly different note we check the alignment of conrods today. I think the one below may be a little bend. But you would have to check to be sure. I think not.

4842 Automotive Engines

How does a four stroke engine work? Name the cycles ,I want to know what the piston is doing and the valves on each stroke. 
Who and what year was the  four stroke engine invented.
What is the purpose of the crankshaft,camshaft,vavles collects(keepers),vavle sterm seals,head gasket,pistons,piston rings name them all, cambelt,flywheel?
What is the bore and stroke.
What i am looking for is a good explaination about each component, use you-tube for videos,


The four stroke engine needs for four strokes to make power. The four cycles to make power are as follows:


Induction- The piston starts at top dead center. The piston then travels down the cylinder and as this happens a mixture of fuel and air is inducted into the cylinder. (induction valve open)


Compression- The piston now at bottom dead center is pushed up. As this happens the mixture of air and fuel is compressed. (both valves closed)


Power- The compressed mixture of fuel and air is ignited by the spark plug and the explosion causes the piston to travel downward. (Both valves closed)


Exhaust- The piston travels upward and the gas produced from the explosion is pushed out the combustion chamber. (Exhaust valve open)

Nikolavs August Otto from Germany invented the the 4 stroke principle in 1876. 

The crank shaft transfers the pistons vertical motion into a torque motion. The camshaft controls when the valves open and close. The valve stem seals prevents oil entering the fuel and air mixture. The head gasket seals the head on the block. The piston is the component being forced down because of an explosion. That is what makes the power. The Piston rings have 3 purposes. The first ring is to keep compression in the cylinder, the 2nd ring is to remove excess oil from the cylinder on the downstroke. The oil ring stores a layer of oil for lubrication. The cambelt keeps the cams in time with the crank. The flywheel bolts to the back of the crank and holds to momentum of the engine. It also provides a place for the clutch to engage to the engine and transfer power to gearbox.