more questions 12/04/11

1.What is the firing order of a four stroke engine?
- the firing order is the sequence in which the pistons do their power stroke. for a four stroke engine the sequence is in order of pistons -1-3-4-2-. 

2.What is the difference between a S.I and C.I engine?
- S.I ENGINE = spark plug ignition. 
- C.I ENGINE = diesel compression ignition. 

3.Is there any difference between a S.I and C.I piston if so what?
- yea the C.I engines pistons have to made to withstand the higher compression and heat. they tend to be larger and have a different shapped crown to the S.I pistons.

  S.I piston

 C.I piston

4.What year was the diesel engine invented and by whom?
- the inventor of the diesel engine was Rudolf Diesel and he invented it in the 1890's

5.What is the purpose of the oil jet on the connectng rod, and where does it spray?
- when the piston travels up to T.D.C the preasurised oil is sprayed up onto the thrust side of the piston so that it lubricates the bore for when the piston travel backs down to B.D.C.

6.On the connecting rod where is the big end and little end?
- the small end of the connecting rod is connected to the piston head and the big end of the connection rod is connected to the crankshaft.

7.What is the purpose of the thrush washers on the crankshaft?
- they prevent the play of the crankshaft from moving to much. but the crankshaft must have a small amount of play to be able to move the pistons properly.

8.On a diesel engine whats the difference between direct injection and a indirect injection type?
- the indirect injection works so that the fuel mixture is not injected straight into the combustion chamber but is injected into a prechamber that then combusts and follows through into the main combustion chamber, were as the direct injection just injects the fuel mixture directly into the main combustion chamber to combust.

9.Explan the term valve timming?
- valve timing is what the name says. its the timing in which the valves for the air intake and exhaust that lead to and from the combustion chamber, are opened and closed. this has to be very presise to make the engine run properly.

10.Why do we have valve clearance?
- 

4 day of ENGINES = FRIDAY FUNDAY

Day 3 ENGINES

Question with Answers

What is taper and ovality in the bore, how is it caused how do you check it?
 - Taper is the difference in width from the top of the cylinder to the bottom 

- Ovality is the the change in shape of the cylinder from circular to oval shaped. this is a different in width of the cylinder commonly starting in the middle working up.

What is side clearance on a piston and how is it checked?
- side clearance is the movement of the piston ring on the piston as it is going through its strokes. as the piston is doing its compression stroke it is moving up compressing the fuel and air mixture. the piston ring is being pushed down. the ring stops the mixture and combusted gas from moving down into the sump. then as the piston moves down the ring is moved up. over time carbons can gather in this gap in the piston around the ring and stop the movement of the ring. this can cause the engine to sease. or taper and ovality. 

How can you tell the difference between a inlet and exhaust vavle and why?
- the inlet valve is larger than the exhaust valve because the inlet need to suck as much air as it can into the engine but the exhaust is just to dispose of the combusted gas.

What sort of tempatures do the inlet and exhaust valves get upto?
- inlet = 250
- exhaust = 750


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?

Pictures from todays work on engine block

engine work done today

Todays work included measurements done on the piston and the slip rings along with measurements on the bore.

First thing was to do a visual check on the pistons and bores.
- piston 1 had a small chip out of it
- piston 4 had 3 small indents on the surface

- bore 3 had 3 pores rust marks around the centre on the stroke section
- bore 4 had 2 long scratches oposite each other on the stroke section. this looks like it has been corsed by someone not being more carefull when removing the piston from the bore.

Next i checked each pistons diameter. this measurement is taken from 90 degrees from the gudgeon pin.
- piston 1 = 78mm
- piston 2 = 78mm
- piston 3 = 78mm
- piston 4 = 78mm

next set of measurements were for the bores. each bore had to be measured 6 times. once at the T.D.C, once at the middle section and once at the B.D.C.  then you must do this twice on X and Y of each bore.

FOUR STROKE ENGINE

How a four stroke engine works

- intake
- compression
- power (combustion)
- exhaust

B.D.C = bottom dead centre
T.D.C = top dead centre

wet sump = four stroke
dry sump = 2 stroke

oil - lubricates
     - heat distribution




1 - air comes through the air manifold and is taken through to the combustion chamber. in this chamber its mixed with fuel and becomes a fuel and air mixture. air is open, exhaust is closed and piston is T.D.C.
2 - the fuel and air mixture is now compressed as the piston rises up. air intake closed, exhaust closed, piston is moving up.
3 - the fuel and air mixture is compressed and the spark plug makes a spark that makes the mixture combust, pushing the piston back down. air intake closed, exhaust closed, piston is T.D.C and plug makes spark
4 - as the piston reaches B.D.C again the combusted gas is released through the exhaust. air intake closed, exhaust open, piston is B.D.C.

Starters

STARTER MOTORS

- A starter motor turns electrical energy into mechanical energy.

the starter uses the voltage from the battery to crank the engine and get it started. it does through a dc motor through magnetics springs and currents that engages the stater gear which meshes with the flywheel.

elctrical magnetic rule- like magnetics repel

if you pass a wire through a conductor it creats a current and a magnetic force

first check is the ocv of the battery.

voltage drop between the battery and the starter. then voltage drop on the solinoid

test current draw. 

if the starter is using up more than the max amps then there could be a compretion problem. engine seezing or big voltage drop in the leads

We started to carry out tests on the starter on our own cars but soon found that it wasnt as easy as having it right in front of you and as my battery died half way through we could not finish our testing. but this is what we recorded.

first we had to identify if the engine was a manual or automatic transmission and wether or not it had any power sorces wuth a memory. to disconnect the battery without causing problems to the memorie you would have to connect an external power source to the car.

we then did the visual check to see if all terminals were clean, well connected and had no corossion on them.

then before we start the testing of voltage drop we have to dissconect the igniton fuel injection system so that the engine can be cranked over without fully starting. then mae sure the vehicle is in neutral. 

we then checked the battery voltage under craking. result = 10v - pass

(although this was a pass it was a bear minimal pass and was quite low for the battery to be cranking under pressure)

we then prosseded with our drop tests.

positive side of the circuit - spec = less than 0.2v - result = 0.23v - fail

solenoid - spec = 0.2v - result = 0.03v - pass

earth side of the circuit - spec = 0.2v - result = /

*After our second drop test my car battery died and need a booster pack to be re started. because if this me and my partner did not finish our test. partly because of the dead battery but also because that we all found how hard it is to do these full tests on a starter on a car not to mention taking one of to pull apart.

in todays market if there was a serious problem with the stater its cheaper and more time saving to go out and buy a new one to be fitted. as long as the problem resides with the starter and not a bad/loose connection or battery problem.

charging system

        AULTINATORS 

-The alternator is was runs all electrical systems and components while the car is running. this is achieved through the battery and the alternator working together, sending signals to one another so that all electrical components can be run.

TERMS AND COMPONENTS 

-the rotor- turns the electromagnit. rotating magnit 

-statar windings- goes around the rotor and is the conductor of the current.

-rectifire- changes/converts ac to dc in the magnit

to do this it uses dioeds.

-diod- one way valve- passes through current one way and not the other

-regulator- controls the amount of volts coming through the battery to be generated by the alltinator by taking signils from the battery. 

- exitor wires- sapply current to the rotors and create the magnit

- to test the alltinator you test the battery with dc volts. normal battery fully charge 12.6 v. the aultinator gives it 13v with no load. half a v more. when the load is put on eg lights and radio the v goes up to around 14.5v.

cooling fan- cools the rectivire. this to cool the diods that heat up

3 diods and one common = 3 phase- 3 positive and 3 negitive and 1 common

                                                        ON CAR TEST

First check is visual. are all warning lights and electricals turned of. check if all wires and connects are good. check alternators belt tension.

Ours passed all these tests. both battery and alternator were a visual pass.

next test is the usal OCV on the battery. ours was at 12.47v. our regulator voltage reading was 14.51v. the spec for this was 13.5 to 14.5. pass.

we then checked the no load amps. ours was 6.5. the spec for this was 5 to 12a for a carburettor. pass. if it had been fuel injected the spec is 10 to 18a. that would have been a fail.

Then we did the load test on the alternator. the charging voltage under load spec = OCV + 0.5V. ours = 14.35. our amps read at 48. this was a pass. 

To carry out this text we had to start the engine, turn on the fan (as the acesorry) and rev the engine up to 2500rpm. using the clamp meter we clamp it arounf output wire B and take the first reading we see.

Our final test was a voltage drop test. 

To test voltage drop we use a multimeter and check the drop between the batery and the altinator while reving the engine to 1500rpm

- drop test 1- B, positive to A output - spec = less than 0.20v - result = 0.07 - pass

- drop test 2 - B, negative to A body - spec = less than 0.02v - result = 0.02 - pass

- drop test 3 - add all drop test reading together for total voltage drop- spec = max allowed 0.40v - result = 0.09 - pass

Summer of the tests we did on the alernator showed us that it was in good running order. all tests that were done on it met spec and passed.

batteries

BATTERYS

in the battery there are led plates that have a flow of elctrons from positive to negitive on either one. the is filled with hydrocloric acid that creates a chemical reaction and produces power.

plates are stored one by one in order positive negitive. with a fine material inbetween each plate to alow the aid to get through but keep the plates from touching eachother and short circuiting the battery.

fully charged battery is 12.6 to 12.75 v

on the top is a negative post/terminal and positive post/terminal. 

how does a battery charge- 

plate 1(positive) pb + O2

plate 2 pb (negitive) 

as they charge it creates H2, so4, 

lead = pb

temperature and battery power.

-80 f = 100%

-32 f = 65%

-0 f = 30%

BATERY MAINTENANCE

first thing you do when checking a battery is a visual check (USE YOUR EYES). go through a rutein of checking the condition. is it covered cirosion, if so then clean it. check the terminals are not loose. is the case distorted. check for cracks or leaks in the case. 

secondly check the volts on the battery. connect the multimeter up to the battery. you should have a reading of at least 12.6v. make sure everything is turned of. if its not at least 12.6 volts try charging it. 

to test the battery you need it to be charged at least 50% = 12.4v. have this on slow charge. if you fast charge a battery it can over heat it and cause swelling.

if this does not work check for surface charge. the way to get rid of surface charge is turn on your lights and leave them on for 2mins.

clean your battery to keep it in the best condition. clean the case or els it can have a build up of dust and that becomes a conductor through the dirt and that draws some of the volts. lube the terminals to keep in good condition.

CHECKS

when checking your battery with the multimeter by OCV (OPEN CURRENT VOLTS) first thing is make sure you have a good contact on the terminals ( that can mean the difference of 6v).

SAFETY

things that can go wrong- battery acid, hydrogen gas, wait. always wear protective clothing and keep away sparks and flames away from them. 

- burning

- electricution

.ALWAYS CONNECT THE POSITIVE FIRST AND TAKE POSITIVE OF LAST.

                                                            -OUR TESTING-

                                        NUMBER ONE TEST = VISUAL FIRST

When we first started testing just the battery to check if it had the right amount of volts we ran into the problem that if you do no make a firm connection on the terminals then you will not get  reading or at least not an accurate one.

Then when we did an OCV test on the battery to check its voltage. we found that it had 12.49v. a battery can have further testing done on it as long as it is above 50% (12.4v) charged.

Our next test was to check the batteries electrolyte specific gravity. for this test we used a hydrometer to take sampiles of each cells fluid. all of the cells tested posotive as all green and in the 12.7 range. things to watch out for when looking at the cell fluid is to see if its murky or clear. if its murky the plates are disintergrating. our batteries specific gravity variation was 0.02. this was a pass for this test.

The next test was a high rate discharge test. using a load tester we load the battery with more amps to see if it can hold up to the pressure that the batter is sapposed to. the amount of amps that you load is half of the cca (cold cranking amps) displade on the battery cover. how load was at 275A. while putting the load on the battery the volts must stay above 9.5v. this load test is to be carried out for 15 seconds max. our resaults were 10v held with a load current held at 275A. this test was a pass.

Our last test was checking the parasitic draw. this is done to check if any components in the car e.g. lights or radio. have drained the battery while the car is off. Our first check is to see if the amp fuse ok. next is to record any radio stations in the cars memory. now check the amp draw. our was 63 amps.

Testing the battery on a car is one of the most important and most simple checks that must be done. alot of the common problems that customers come in for are battery related e.g. dead battery. flat battery. or even just poor mantinence like cleaning.