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

Taper - difference between the measurements of A1 B1 C1 and difference between the measurements of A2 B2 C2. 
That caused by the piston rings rubbing on the cylinder walls. 
To measure it, place the cylinder-bore gauge across the cylinder, just below the unworn ring ridge, move the gauge slowly up and down to measure taper at top middle and bottom of the ring travel in cylinder.

Ovality(out-of-roundness) - difference between A1 and A2.
May caused by unequal pressure on the piston.
To measure it, place the cylinder-bore gauge across the cylinder, just below the unworn ring ridge, move the gauge slowly up and down to measure A1, turn the gauge 90° in the cylinder to measure A2. 

What is side clearance on a piston and how is it checked? 
Side clearance  about 0.02mm to 0.05mm.
Using a micrometer, measure the diameter of piston at a point about one-third of the skirt height, and compare to the diameter reading measured from cylinder bore.


How can you tell the difference between a inlet and exhaust valve and why?
Inlet valve always lager or more than the exhaust valve.
Because  lager or more inlet valves reduce intake resistance, allow lager intake passages and freer flow into cylinder.

What sort of tempatures do the inlet and exhaust valves get upto?
Inlet - 150~250°F / 66~121°C
Exhaust - 1000~1500°F / 538~816°C


What temperatures and speeds must the piston be able to cope with?
Temperatures - Around 230°C at the top, and around 100°C at the skirt.
Speeds - Around 16m/s for automobile engines, and around 20–25 m/s for sport automobile engines or motorcycles


Why do we have piston ring end gap clearance ?
Because when engine is running, the piston ring get hot, needs room to expand.

What could the result be if the piston ring end gap is too small?
If the gap is too small, the ring will have no room to expand when it gets hot.



Why do aluminum cylinder heads usually have a steel shim (washer) between the valve spring and the 
cylinder head surface ?
Because the valve spring needs to move up and down lots of times, could damage the aluminum cylinder head, steel has better intensity than aluminum, also shim can adjust the valve length to control the valve seat pressure.


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?
If there is not margin or thickness at the edge of valve, will cause the valve head to overheat then the edge will burn.

What is the purpose of a core plug?
It is used to remove sand from the casting when the engine block is cast.

What is end float and run out on a crankshaft, hows is measured?
End float - alignment at the end of crankshaft.
Run out - alignment at the journal of the center bearing.
How to measure refer to the pictures:

                             End Float

                             Run out