Mongoose MGX single speed conversion

[rickpaulos]

Well I didn't take any before or during photos. Here is a 'before' I got from the www.


The donor bike was being scrapped out at the local bike coop a couple years ago. I decided to rebuild it as a single speed bike. After 2 years, I got around to working on it some more. The frame is all steel.

I used the angle grinder to remove the cable stops and rear brake studs. Touched up the paint with black. I know I don't have that color of yellow to match so I used black on the yellow. yeah, it's ugly. To keep the ugly theme going I went with a red rigid fork, purple handlebars, grey tires, 1 silver crank, 1 black crank, etc.

I built the rear wheel with a coaster brake hub spoked to alloy rims. Front wheel has a QR axle.

Crank arms. Well most of these cheap bsos have chain rings riveted or welded together. Some of those rivets look like bolts but are not. Riveted rings are easier to remove. Angle grinding off the heads of the rivets leaves an easy tap out with a punch. The spot welded rings mean grinding the unwanted rings to oblivion. That leave the 1 ring that is swaged to the arm. Sometimes its the large ring, some swaged the middle ring, some swage the small ring, some swaged 2 rings. So you need to select a crankset that will have the 1 ring size you want. In this case it's about a 38 or 40t. Also, the cranks with the smaller rings swaged on mean a better chain line.

The rear suspension on this bike is an URT so varying chain tension isn't a factor BUT the vertical dropouts are a problem. Trial and error got me a 16t that works well without too much chain slack. The 18t and 15t didn't work. I used a brand new chain that isn't worn. Another method of getting the chain slack just right is to test fit a bunch of worn chains to find one that is just right.

A brief test ride late at night (no decent photos possible) revealed the gear ratio is okay. I need to change the top headset race to make it ready to go.

More photos soon.

Rick

 

[rickpaulos]

Just a comment on boxmart bsos. They look like mountain bikes but they were not designed for off single track trails. They are low quality copy cats that do not use the materials or have the engineering and testing behind them that good bikes do. They copy the look and style but none of the traits that make them trail bikes. In fact many have decals on them that state "Not for off road use". IMO, the frames are often bomb proof and the bikes are typically equipped with gears and brakes that barely function. And the fake shock forks are just awful. Internal springs with plastic sliders for friction dampening that are subject to many recalls for bad welding. I've found many nuts & bolts have threads made so bad they barely engage the parts the are meant to secure. But these bikes make okay source material for rebuilds. Remove and recycle all the bad parts and start over.

Rick

 

[horsefarmer]

Rick, you are right on there. As with much of this big box junk, a thorough revision in necessary so turn it into a useful bike. I am currently revising a Huffy Premier from WallyWorld that has a Very sucky coaster brake and likes to throw the chain.

 

[rickpaulos]

photos.

I took it for a short ride. A bit chilly out so I didn't go far. Plus, like most boxmart bikes, it's a bit small for me. It would fit someone 5'6" pretty well. The gearing seems about right for townie use.

I noticed the frame has 4 bosses on the underside of the downtube. 2 for a wb cage and 2 for what, a mud deflector for downhill racing? Not on this bso.