What do BDC and TDC mean in motorcycle jargon?

Answer

According to Timberwoof, the maintainer of the rec.motorcycles FAQ:

• BDC means Bottom Dead Center, the position closest to the crankshaft that a piston travels in its cylinder. Alternatively, Brain-Dead Cager (refering to a car, cage, driver that is not attentive to the road: especially motorcycles on it). "When the piston hits BDC."

• TDC means Top Dead Center, the position closest to the cylinder head that a piston travels in its cylinder.

YEs...

BDC is the lowest point of the cylinder till where the Piston can move and simillarly TDC is the top most point till where the Piston can reach. Both of these are limited by the crankshaft and connecting rods, not the cylinder itself.