Bicycle Mechanics - Rear cassette self destructing?!?

Hello and thank you all for this awesome site. I currently have a trek 7.2 which I love, but I also have a Next Avalon which has been holding up pretty good for a beater. So here's my question. I took my avalon for a ride yesterday and about ten miles in I heard this awful clack clunking coming from the drivetrain. I stopped and found the threaded part that holds the rear cassette together had come loose, so I tightened it by hand and continued carefully home. When I got home I dismantled it and reassembled it with proper hand tools and tightened the cassette holder. Then on my morning ride it started the same noise again...

any ideas what is going on here?

p.s. it has 7 speeds shimano rear deraileur well oiled chain

and my apologies for a question involving a next bike....

By cassette holder, I assume you mean the cassette lockring. If so, the required torque for those is 40 N*m or 25 ft. lbs. This is a considerable amount of torque. What did you use to tighten the lockring? Chances are you just didn't get it tight enough.

However, I wouldn't expect a Next branded bike to use a cassette. Can you post a picture of the problem area?

Take the cassette all the way off and inspect the freehub body. It's not a common thing but freehub bodies and/or lockrings can crack, inspect the lockring too.

here's a pic

the whole set of gears are loose

That is a freewheel, not a cassette. Nevertheless, it seems to have a cog-retension-lockring similar to a cassette.

Is the smallest cog threaded onto the freewheel or is it splined?

it is splined, actually the whole freewheel hub feels loose with the gears removed...hmmmm I'm sure I'm close to the problem but I just don't have the knowledge....

another pic

I'm familiar with those freewheels, but not if there's a tool to tighten them.

They operate on the same principle as a cassette. 6 cogs are spline the last screws it all together. check the threads on the small cog and the freewheel body. If any of them look stripped or missing metal in the threads then replace the freewheel (you will need a tool for this, or take the wheel to you local LBS to get them to do this) A cheap freewheel should run anywhere from 15 to 25 dollars, if you have to purchase a tool then add another 8 to 15.

since you have it apart i would go the replacement route, especially if it is indexed...

Upon further dis assembly I found the freewheel and hub/axle were loose. Thankfully the bearing surfaces look and feel ok, so no damage there at least. Digging even further I found the axle has a slight bend in it...:twitchy:

So it looks like I'm in for a new rear wheel build up...oh well at least its on this bike and not my trek...