Theory questions

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

Taper and ovality is the wear of the cylinder bore caused by the side to side movement of the piston. If the cylinder bore is tapered then you measure the diameter of the top and bottom and the middle of the cylinder bore

To check the ovality of the cylinder bore you measure the circumference of the cylinder bore, instead of the bore being round it will be oval shaped

What is side clearance on a piston and how is it checked?
The distance between the piston and the cylinder wall. Piston rings close this gap under pressure to create compression in the cylinder. to check the side clearance on a piston insert the ring into the piston and use a feeler gauge in between. 

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

The inlet valve is larger than the exhaust valve to allow more air/fuel mixture into the engine. The exhaust valve only needs to get rid of the burn remains

What sort of tempatures do the inlet and exhaust valves get upto?
inlet valves get up to around 250 degrees Celsius
Exhaust valves get up to around 750 degrees Celsius

What temperatures and speeds must the piston be able to cope with?
pistons must be able to handle temperatures up to 300 degrees celsius and handle rotations up to 7500rpm

Why do we have piston ring end gap clearance ?

Pistons rings ensure there is a good combustion seal in the cylinder and help with heat transfer from the piston to the cylinder wall. The end gap clearance allows for expansion of the ring under heat and compression

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

When the engine gets up to operating temperature and the piston rings expand from heat it can cause overlapping or bending. can also cause closure of the end gap, damage to the bore, the ring breaking and even the pison siezing up.

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

Over time the valve spring lose tension. Adding a steel shim would bring the spring tension back up to spec

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

S.I is spark ignition. It uses a spark plug to ignite the air/fuel mixture at the top of the compression stroke like in petrol engines

 
C.I is Compression ignition. It uses highly compressed hot air without spark to ignite the fuel like in diesel engines. On the compression stroke only air is introduced to the combustion chamber and at the very top of the stroke the fuel is injected into the hot compressed air.

What is the purpose of the margin on the valve?

Helps dissipate heat from the valves. The exhaust valves have a thicker margin than the intake valves because the exhaust valves encounter more heat. if the valve margin is too thin then the valve will become too hot when exposed to combustion and it will burn.

 What is the purpose of a core plug?
Core plugs are used to plug the core holes that are left by the casting of the block. Sand is used to create the paths for the water cooling and leaves holes on the outside of the block which are plugged by core plugs. If the engine doesn't have antifreeze in it and the water in the engine freezes, core plugs are supposed to pop out as the freezing water expands. without the core plugs the engine block could crack.

What is end float and run out on a crankshaft, hows is measured? 
 End float is the slight movement you crankshaft is allowed to move in the main bearings while the engine is cold. Using a DTI gauge at the end of the crankshaft, lever the crankshaft side to side to get the measurements of the crankshaft play. Alternatively you can push the crankshaft to one side and use feeler gauge inbetween the crankshaft and a thrust bearing.