Mode Bottom Bracket Failure?

[Lifelover]

What does it sound/feel like when a bottom bracket of failing?

My 16 y/o son has a low end GT MTB that he uses as his get around bike. He was telling me that it needed a little TLC because it sounded like the chain was really rusty or something. After a good lube and clean up I took it for a test ride and thought the damn Frame might be cracked.

At the top of every pedal stroke it makes a nasty metal on metal sound and you can actually feel a slight clunk. I gave the frame a quick look over and can see no signs of failure. Everything is tight on the drive chain. Just spinning it by hand (with chain still on) I don't really feel much in the BB?

Any ideas?

[rePhil]

Remove the chain of the chainrings, put your ear on the saddle and give the cranks a spin. If it's crunchy you will hear it.
Poor mans stethoscope.

[Peter P.]

Remove the crankarms and spin the axle like a safecracker. It should be obvious then.