What is top overhaul?

Top overhaul means that worn out compression rings and oil rings will be replaced with new set of rings for the engine to run in full compression ratio. This means also that valve seat must be set properly same with rocker arms and camshaft. It is done by removing the oil pan and from under remove the connecting rod bolt and push each piston assembly together with the connecting rod upward. After a thorough inspection of each parts replace all the parts that shows wear specially connecting rod bearings set again to standard size. After some machine shop works on the cylinder head everything can be retrofitted again to the engine block. And after setting all the necessary timing you can now start the engine to see if your work will turn out fine.




So this is done on my engine. 

After assembled

After removing oil pan

After disassemble from engine

Cleaning the head manually using fine sand paper

Cleaning the head

crankshaft before

crankshaft after cleaning

Signs You May Need a Rebuild

There are some frequently seen signs that a rebuild may be necessary for your engine. The most common sign is oil consumption and excessive white smoke in the exhaust, especially when the engine is cold. This is normally a sign of worn piston rings. More extreme signs could be metal shavings in the engine oil (a common sign of dangerously worn bearings) and "knocking" or "chattering" from the engine bearings.

Installing crankshaft

valves before cleaning..full of carbons

adjusting tappets

cleaning with acids

p/s: I didn't need to replace piston rings since its still usable. 

Sources: wiki, russles and howto