Why the cause of white smoke can be determined by oil loss via the valve guides
(1) The negative pressure of the intake manifold is high when the engine is idle, so oil is sucked into the combustion chamber from the valve stem. However, the temperature in the combustion chamber is low, so the oil attaches to the carbon, etc. and accumulates on the valve or combustion chamber, decreasing the amount of white smoke.
(2) When racing the engine from the above state (1), the temperature of the combustion chamber increases, instantly burning the accumulated oil, causing a great deal of white smoke to discharge. When the oil is completely burnt, the amount of white smoke decreases.
(3) If the engine is continuously raced, the temperature in the combustion chamber rises, so even if the oil is sucked in, it is burnt before accumulating, therefore decreasing the amount of white smoke.

Engine disassembly inspection
• With oil loss via the piston rings
A lot of carbon attaches to the outer circumference at the top of the piston.
• With oil loss via the valve guides
A lot of carbon attaches to the intake valve face, at the top of the piston, or to the exhaust valve stem. In addition, oil can also attach to these parts, making them wet.
When oil loss via the valve guides is discovered, remove the intake and exhaust valves and inspect the conditions at the face and stem.