Bicycle Mechanics - creaking bottom bracket/crankset

My bike ('83 Bianchi Nuovo converted into a fixed gear) has been making an ominous creaking noise on the downstroke of both sides. It's been getting progressively worse and I think I've felt something slip a couple of times (though I can't be 100% sure about the slip).

It's a really low pitched creak and it's definitely coming from that bottom portion of the frame. I've popped my chainring off, adjusted the chainline and put it back on. This seems to reduce the noise for a while, but then it just picks right back up after 10-15 miles. None of my chainring bolts are loose at this point. I've also re-tightened my pedals, thinking that might be related.

My bottom bracket probably hasn't been taken apart since the bike was put together initially and it doesn't sound too great (gritty, needs lube) if you spin it without the chain attached, but it spins just fine. I've not been able to remove the bottom bracket in the past, so I may just need to break down and take it to the coop and use a vice.

Anyone have any thoughts as to what might be creaking? This is my primary means of transportation and I'm afraid that something is going to snap at some point and I'll end up a stain on the road. :cry:

Thanks!

A creaking bottom bracket isn't a sign of imminent failure but you should still fix the issue. What type of bottom bracket is it? If it's the cup and cone style, you can easily go in and clean the internals and add new grease. However, you note adjusting the chainline which makes me think this may not be a typical bottom bracket. Regardless, a vice is usually only necessary if you are completely removing a fixed cup of a cup and cone bottom bracket (and one that has become stuck in the frame from corrosion), which is not necessary for a simple regreasing. You will need the proper tools to remove/adjust the bottom bracket though. If you do not have these, go find someone who does before attempting any repair.

Sounds like it could be the BB (it really hasn't been serviced since 1983?). However, I recently had a creaking that I thought I had narrowed to the BB (tightened pedals, tightened a loose chainring bolt, tightened seat post, changed worn cleats, etc.) and I still had a creak so I took it to my local bike shop. They diagnosed it as a loose headset. They had moved the spacers a couple of months before while sizing my bike and it had come a little loose. I couldn't feel any movement. It fixed the problem. "BB" creaks can be very difficult to diagnose because every sound seems to radiate from the BB area, especially with oversized tubes in today's carbon frames. Good luck.