OK I bought this Mongoose from Walmart with the full intention of sprucing it up and giving myself some hands on bike repair techniques. Here is a picture of stock bike after assembly and tuneup, it rides sweet.

Stock + Seat
I decided to install a new stem and a new crankset with external sealed bearing bottom bracket. Thanks to “superbug” at ” BigBoxBikes.com” forum for pointing me to the Shimano Deore LX crankset from ” Jensonusa.com ” . A fairly inexpensive set but high above the stock parts. The stem was easy, I knew what i wanted so I got 1 off “amazon.com” .

Adjustable stem
Much better for me and comfotable for riding. This might not be best for aggressive off roading, but I like it, and its nice and solid and lighter.
Next up were the cranks. Old ones:
Removing these and installing new ones is not for the faint of heart. I got the pedals, crank arms, and left side set ring and bearings off just fine. Then came the “Fixed cup” side of the Bottom Bracket. OK, These things must be torqued on by an army of of dedicated factory workers. I tried a few methods, the 36 mm bracket wrench, backed up with a series of bolts and washers to hold the wrench tight to the nut. No joy. I tried a series of lock washers and and bolts, again no joy. Here is what worked , and easily too. A dremel with a cut off wheel. One Caveat though, be very careful not to cut into the aluminum case of the BB. Go slow and check your work often. Cut a vee in the fixed cup in the middle of the curve on top and below the flat sides of the cup.Cut all the way through the metal of the cup and into the recess of the spindle hole. Now get yourself a good 1/2″ cold chisel and knock out the vees you just cut. Spray with a loosening agent like “Liquid Wrench”. Tap Tap Tap the cup. Now position chisel and smack that dang thing with a hammer(Put on your damn Safety Glasses) till it breaks free. Do not in any way, shape, or form, hit your hand or aluminum part of the frame. BINGO now you are home free. See picture So the rest was a piece of cake .

Cup removal
Lots of info on line if you need more pointers.
Here is the new crankset, I used 1 spacer on each side of the external bearings and had to raise the front deraileur about 2 to 3 mm. This turned out to be a real learning experience for me.

Shimano Deore LX