Its the one involving the collection of 3 specific items and placing them in a vehicle. I've watched a Youtube video that shows you exactly how it's done but it's not unlocking for me. I'm sure someone here knows what achievement I'm talking about. I need tips. 
 
Here's the video to show what I'm trying to do: 
  

Try it again? It worked the first time for me, and I followed that video as well.

" @JJWeatherman: I recreated the vehicle that was used in the video. "

The guy says something about taking the pieces down to an airlock too. I wonder what that was all about.

"Inside the Terranium of Terror, you need to have a fuel tank, rocket and license plate in your vehicle all at the same time. You need to have a large enough vehicle that all three can rest on the bottom or the achievement won't work. You can't have the license plate resting on top of the fuel tank for instance. The game needs to register all three on the bottom of your vehicle. You can use a custom vehicle or the Humba Big Loader would work as well."
 http://www.xbox360achievements.org/game/banjo-kazooie-nuts-and-bolts/guide/

OK I just got it. I ended up using the "large box" as the container for the items. Despite it being fairly small and hardly being able to hold all of them, I unlocked the achievement instantly after I placed the last item in.  
 
Hopefully this will help out someone in the future. Remember: Use the "large box" if you have it availiable.