The Walmart Special (Kent Fixie/Single Speed 700c)

For this build I am using the Kent Fixie 700c, available from walmart for a cool one hundred bucks. I picked this frame due to its simple construction, consistent narrow tube diameter, wide pedal crank and low price. I initially wanted to buy a Thruster 700c (which is basically the exact same bike) but there were none available. Another deciding factor for this frame were numerous successful motorizing projects that I found via google and youtube. The bike I got was kind of sloppy (misaligned wheels, crooked brake pads, slightly crooked handlebars) but all those can be fixed pretty easily.


Not bad looking at a glance but a closer inspection reveals pretty humble components. Love the red tires though!


The bike has a very narrow profile due to the short handlebars. I'll definitely be careful on turns with this thing.


The rear hub with a single-speed gear and fixie gear. The builds I've seen have attached the engine drive sprocket to the fixie gear, but I'm considering a Manic Mechanic clamshell mount.


My mental estimation is the chain should have a very good path to the engine mount, and the idler pulley won't give me nearly as much trouble as my last build.

The engine kit I will be installing is the flying horse 66cc from bikeberry.com. I've had good experience ordering several individual parts from them before, and they are an established business who have to maintain some level of responsibility for delivering orders (my last supplier screwed me over). I have a dual-cable brake lever that I'll install to free up the left handle for the clutch.

I'm waiting on the engine delivery so probably not much more news until next week.

 

[darwin]

Cool bike, that seats gotta go though. On the rear wheel a sprocket comes on both sides? Is one bigger than the other for different gear ratios? Just flip the rim and that's it? What's the difference between a single speed gear and a fixie gear? Sounds like the same thing.

 

[BlueDestiny]

A fixie gear will turn the wheel both forward and backward, enabling you to brake by holding the pedals steady or pedal the bike in reverse. However, any time the bike is in motion the pedals will be moving with the wheel. A single speed gear is the standard bike gear that only rolls the wheel in one direction, letting it spin freely otherwise. The bike comes with both styles on the rear hub and you can switch them by flipping the wheel.

 

[butre]

On account of the useless gear ratio, flip flop hubs don't necessarily work too well for motorizing other than with the traditional rag joint method (which I'll never recommend) unless you're the king of welders and can weld a larger sprocket to the fixie cog perfectly centered. That particular one won't work with a manic mechanic adapter without expensive custom machined radiused reducer bushings.

My suggestion would be to relace that rim with a Shimano CB-E110 (or buy a rim that already has one) and use a manic mechanic adapter on that.

That bike has an attractive design though, how much does it weigh?

 

[darwin]

Assuming the fixed sprocket is on the left side in above pic, not sure but say it is. It must be threaded on. Couldn't you put a cassette type sprocket on there instead of the fixie? Seems if you could that would be a great/reasonable solution to the clamshell......one other minor point on the bike is it doesn't have v brakes which I prefer.

 

[BlueDestiny]

Oh yeah I wouldn't put the drive chain on the fixie gear but several builds have mentioned they could mount the rag joint sprocket on the fixie gear somehow. I'll have to see how it will work when the engine arrives though, and I don't have a problem with the usual rubber-sandwich rag joint mount.

The bike weighs about 28 pounds.

 

[Timbone]

I motorized aa 700c bike, one very similar to this. If you do a traditional, simple build (motor drive left side, no jackshaft), your clearance on the left chainstay will be TIGHT. You might want to do a mock up build to see where the chain will run and be prepared to stretch the stays to get an extra bit of clearance. If you let a 415 chain whip the frame it will eat it up.

I think even rolling with 700c x 35's, you are asking for pinch flats. A sixty pound bike rolling at 25mph i hell on skinny tires. I am an advocate of 26" wheels with a minimum width of 1.95 inches.

Good luck!

 

[BlueDestiny]

Thanks for the info! I'll definitely keep an eye on the tires and chain clearance. As for mounting the sprocket on the fixie gear, I found a thread where someone did exactly that on the same model bike, with pictures. It looks like the sprocket bolts fit into the teeth of the fixie gear, but the assembly is a bit sloppy. My biggest worry with this build is actually the exhaust pipe due to horror stories about the mounting bolts shearing off, but I can probably scrounge up some aluminum to bend into a bracket mount.

 

[professor]

My 2 cents is the bike is totally wrong for motorizing.

The caliper brakes are poor (well, better than a single coaster brake) and one day you WILL need to stop NOW and will not be able to.
I prefer to avoid pain and injury or worse.

Hooking up a dual brake lever to an already wimpy brake deal renders the force you are able to apply (with one hand rather than 2) into 1/2 of the effort at the wheels.
This is not considering the possible difference in pivot point and lever differences.

Seriously, think about a bike with a minimum of 2 V brakes and bigger around tires.
The feature of having gears is great too, as is a spring fork.

 

[darwin]

Thanks for the info! I'll definitely keep an eye on the tires and chain clearance. As for mounting the sprocket on the fixie gear, I found a thread where someone did exactly that on the same model bike, with pictures. It looks like the sprocket bolts fit into the teeth of the fixie gear, but the assembly is a bit sloppy. My biggest worry with this build is actually the exhaust pipe due to horror stories about the mounting bolts shearing off, but I can probably scrounge up some aluminum to bend into a bracket mount.

Do you have a link to those pics or can you post the pics, I'd like to see how it looks.