Questions 2

1.What is the firing order of a four stroke engine?


The engines we are working on: 1-3-4-2


2.What is the difference between a S.I and C.I engine?


SI - Fuel ignited by a spark created by a spark plug
CI - Fuel ignited by heat in the cylinder created by a glow plug and the compression of the fuel and air.


SI - Uses petroleum fuel
CI - Uses diesel fuel


SI - Compression = 6-10 psi
CI - Compression = 16-20 psi


SI - During suction stroke fuel is allowed into the combustion chamber
CI - Towards the end of the compression stroke the fuel and air mixture is injected into the combustion chamber and almost imediately ignites due to diesel having a lower combustion temperature.


CI - heavier due to it needing to handle higher preasures in the combustion chamber than the SI


SI - Produces higher speeds
CI - produces lower speeds


SI - pistons


3.Is there any difference between a S.I and C.I piston if so what?


The C.I piston needs to create a larger compression as there is no spark to ignite the fuel, therefore has a different shaped piston


CI                                        SI
4.What year was the diesel engine invented and by whom?

1892 by Rudolf Diesel, German Inventor

5.What is the purpose of the oil jet on the connecting rod, and where does it spray?

It sprays oil onto the walls of the cylinder with every revolution of the crankshaft. It's purpose is to lubricate the piston as it moves up and down the bore and also the piston pin.

6.On the connecting rod where is the big end and little end?

The big end is where it is conected to the crankshaft. The small end is where it connects to the piston with the piston pin.

7.What is the purpose of the thrust washers on the crankshaft?


To cut down on end float.8.On a diesel engine whats the difference between direct injection and a indirect injection type?




Direct injection the fuel is injected straight into the combustion chamber.
Indirect injection the fuel is injected into a seperate chamber.9.Explan the term valve timing?

At which point each valve is open in respect to the other and position of the piston.
A couple of terms are:
Lead: intake valve opens before TDC and exhaust valve opens before BDC.
Lag: intake valve closes after BDC and exhaust valve closes after TDC.
Overlap: intake and exhaust valves are both open for a few degrees around TDC of the exhaust stoke.


10.Why do we have valve clearance?

When the valve train gets hot, it expands. The valve clearance gives it room to do so. If this wasn't there the valve wouldn't shut properly and may cause fuel to leak or the valve to burn.

Misc Engine Questions

What is taper and ovality in the bore, how is it caused how do you check it?

Taper is the difference in measurement between the top and bottom.

It is caused by the piston rings wearing down the sides of the bore when they rub past it during the piston movement.

Ovality is the difference in diameter A to diameter B
Eg. creating an oval shape in the cylinder.

This is caused by the piston rings applying more pressure to one side of the cylinder than the other. This creates more wear on one side and less on the other making it slightly oval in shape

What is side clearance on a piston and how is it checked?

It is the gap between the piston and the bore.
Using dial bore gauge, measure cylinder bore. Measure piston diameter. Subtract piston diameter from cylinder bore diameter to get piston side clearance.

How can you tell the difference between an inlet and exhaust vavle and why?

The inlet valve is bigger because it is harder to draw in the right amount of air and fuel. The reason why it is harder is because it relies on a vaccuum created by the downwards motion of the piston.
The exhaust gasses are easier to expell so dont need such a large valve to get rid of them. This is because pushing them out rely on the piston physically pushing it out which is more efficient than using a vaccuum and the valve only needs to be small.



What sort of tempatures do the inlet and exhaust valves get upto?

Inlet valves: 250 degrees
Exhaust valves: 750 degrees

What temperatures and speeds must the piston be able to cope with?

300 degrees for the piston heads.
30 m/s for the spead they need to withstand.

Why do we have piston ring end gap clearance ?

To allow for expansion. When the piston ring gets hot it expands.

What could the result be if the piston ring end gap is too small?

If the gap is to small, when the piston ring expands both ends will touch each other then push out against the cylinder. This can result in the engine ceasing up and/or wear or major damage will occur to the cylinder.

Why do aluminum cylinder heads usually have a steel shim (washer) between the valve spring and the cylinder head surface ?

It is used to restore the spring tension. The reason is it adds material to the spring which has been lost through wear

It also stops the moving spring (which is a harder metal than the cylinder head surface) from wearing down the cylinder head surface by puting a barrier inbetween the two.

What is meant by the terms S.I and C.I in a four stroke engine?


S.I - Spark Ignition
C.I - Compression Ignition

What is the purpose of the margin on the valve?

It is to allow for expansion when the valve heats up. If there wasn't it would jam and cease up the engine, possibly bending or breaking the valve.

What is the purpose of a core plug?

The core or frost pluga are used to fill the core holes. (The core holes are created in the casting process to allow the casting material to be removed.)

What is end float and run out on a crankshaft, hows is measured?

The run out on a crank shaft is the difference, when the camshaft is turned, around the journal. Measured with a DTI guage.

The end float is how much the camshaft moves foreward when pushed foreward through the crank caps/bearings. Also measured with a DTI guage.

Four Stroke engine Question answers

How does a four stroke engine work?

Stroke one the piston is travelling down from TDC to BDC and the Intake valve is open allowing the fuel and air mixture to enter the combustion chamber and the Exhaust valve is closed.
Stroke two the Intake valve closes and the piston travels to TDC compressing the fuel ready for combustion/ignition.
Stroke three the Intake and exhaust valves are both closed. The spark plug ignites the gasses and pushes the piston back down to BDC.
Stroke four the exhaust valve opens and the piston travels up to expell the burnt gasses.
Cycle starts again.

Who and what year was the  four stroke engine invented.

Nikolaus August Otto invented the 4 stroke in 1862

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.

Bore is the diameter of the cylinder.
Stroke is the distance from Top Dead Centre to Bottom Dead Centre