I remember departing the old Hong Kong Kai Tak airport on runway 13 in a 747-200 freighter. We were relatively heavy and the temp was just over 100 F. The lower cargo trim air "heaters " were in yellow "too hot shutoff" because of ambient heat, and verified by the local mechanics....When we began the takeoff the #2 engine ran a bit differently than the other 3, but nothing out of parameters. Right as we hit V1, but still about 10 or so Knots below Vr the cockpit filled with smoke, and it was thick enough that you could barely see the instruments , that is you could see them but not read numbers or print on them.....Well we had to sit there and chug up to Vr first since we were past V1 and that seemed like forever......The Captain called out "Smoke in the cockpit" and so we goggled up and O2 masks about while rotating or so it seemed, got up to cleanup alt....I was a Second Officer at the time..There wasn't really a QRM proceedure for that scenario at that time but we closed the bleed on engine #2 and turned on 1 AC Pack, and then I was tasked with putting on the ols SCBA breathing gear (before pbe's were invented) and looking for the source of the smoke in lower E&E and the main deck cargo....On the main deck the smoke was so thick that you could only see about 2 pallet positions back when I began my circuit around the cargo...The power of adrenaline is note worthy, in that I had about 30 lbs of breathing gear on my back and a huge extinguisher 40lbs and still made it around the whole main deck before the airplane got to 5000ft....in that time the smoke cleared quite a bit and we could see it was "blue tint" which meant it was of engine bleed source... The #2 engine went on oil watch, with the bleed wire closed and we decided to take a couple of days off. The idea of doing an IGS to 13 at Kai Tak with a cockpit full of smoke and a main deck fire is scary at best good it was bleed, but we had a lot of possible sources to worry about in a very short time...That was my scariest day even as I tell it it is hard to do it justice.