(Assuming you are starting with a good, tight engine)
PHILOSOPHY: Minimize internal friction and impedance to fuel flow – no timing changes.
Carefully disassemble the engine and place the parts in a jar.
Pour in equal parts of lacquer thinner and methyl alcohol to just cover the parts.
Loosely seal the jar and place in a pan full of hot tap water for about 15 minute, swirling it gently a few times.
Remove the parts and blow them dry with compressed air. Examine everything to insure that it’s meticulously clean. Remove any signs of rust, especially in the cylinder. Fine Scotchbrite works well.
With a Dremel and the smallest bits and stones you have, carefully break any sharp edges in the fuel path.
Crankshaft – the rear inner edge of the intake port usually has a burr – round it slightly. Where the inside bore meets the crank flange, remove the sharp edge and flare the hole. Smooth off all the sharp edges on the crank flange and counterbalance. With a soft cloth, polishing compound and crocus cloth, gently polish the inside bore, main bearing and crank pin. I’ve heard of drilling a hole in the crank pin but I have not tried it.
Connecting Rod – Remove all casting marks and edges. Polish the rod to a high luster. If you have a # 75 80 drill, drill an oil hole at the lower side of the lower end. Deburr the hole.
Case – smooth off any sharp edges on the inside. Flare the top of the vertical by-pass ports. Polish the inside.
Wrist pin – polish the ends and running surface like a mirror.
Piston – Relieve it. Decrease the diameter below the wrist-pin hole by about .0005”. You can verify the clearance by gently placing the dry piston skirt-down in the top of the dry cylinder. Turn the cylinder upside down and the piston will fall out.
Cylinder – there are three by-pass ports. VERY carefully remove any burrs at the lower opening and flare them very slightly. Don’t touch the bore side of these ports.
Backplate – polish the front face.
Head – needs nothing.
Blow off all the parts with compressed air and insure that there are no chips or polishing compound anywhere. Put a drop of oil on the wrist pin, crankpin and crankshaft main bearing. Carefully reassemble without gaskets on the lower cylinder or backplate. If you suspect leakage, put a tiny, thin film of RTV on the surfaces.
Before installing the head, put a few drops of oil in the intake and in the bore, then turn the engine a few turns. It must turn smooth-as-silk. Install the head. If you feel ANY interference at TDC, add the needed number of head shims.
That’s al I do. I do nothing to the NVA except a meticulous cleaning.
HAVE FUN!!!