OK, I'm going to sound like Operator here and say that this is positively the worst suggestion I've read on this forum EVAR! There's simply no guarantee that the oil would actually reach the bearings without it running out the likely drain hole in the BB shell. And if it turns out to be a sealed cartridge BB then the oil wouldn't even see the bearings. And even if there is no drain hole or he pours it in quickly enough it would take the better part of a quart of oil to fill the BB shell AND the lower portion of the downtube AND the chain stays before it actuall reaches the bearings. I have yet to see a frame where at least the downtube is not joined into the BB shell with openings to allow the air pressure to equalize during welding. And pretty much all lugged bikes have openings into the chain stay as well. At the very least this will create quite the oil puddle and at worse it won't achieve anything.

Ablang, if your hearing crusty grinding noises coming from the bottom bracket then it's time to either have the BB serviced correctly or replace it with a new sealed cartridge BB. If it's one of the cup and cone separate bits BB's then it MAY be servicable. But if it's noisy then it's more likely that it's gotten rusty and pitted in which case it requires replacement. Since I gather you don't have the various specialized tools to do the swap you'll find it's cheaper to take it to a shop and have them replace the BB. If you want to learn and build up your tools then visit the Park Tools site and go to the Repair Help page. Then click on the crank area of the bicycle they have there when the label pops up. The page it takes you to will fully describe what tools you need and how to do the job.