BlueWindbreaker

I have a Murray three speed bike that has a single speed freewheel for some reason. I got it for free and the tires would need to be replace. It’s worth less that 50 dollars. I want to convert it to a fixed gear but don’t want to buy a new wheel so I was thinking of just crippling the free wheel by soldering it. Is there a way that this should be done? Is there a different way to cripple the freewheel so I can ride backwards?

TejanoTrackie 

First off, you would have to weld it, since soldering is too weak to carry the load. The problem will be that when you try to backpedal, the welded freewheel will unscrew from the hub, since there is no lockring. You could, of course, tighten it with red Loctite to create a suicide hub, where the freewheel would be permanently bonded to the hub and could not be removed. As long as you keep brakes on it, it will be safe in the unlikely event the welding fails or the freewheel somehow manages to unscrew itself.

veganbikes

I would not recommend trying to convert a freewheel to a fixed gear with a non-fixed gear hub. As TejanoTrackie suggested you could do some sketchy stuff with welding and a heavy threadlocking compound but it is not a good safe option and should be understood as a do at your own risk and know it is not really worth it.

I would just ride the bike as is and save your money and time for a proper fixed gear you want.

JohnDThompson 

Are you certain that you have a freewheel? Most 3-speed bikes use an internally-geared hub, with the ratchet mechanism inside the hub, and the sprocket is usually a simple splined sprocket and held onto the hub driver with a circlip. Is there a brand/model marking on the hub? Can you post some pictures of the hub and sprocket?

I suspect that in order to convert to a fixed gear, you will need a different wheel.

somedodo

if you have the hub, how difficult/complicated is it to switch a bike from single speed to fixed gear (or vice versa). would it be better to have one bike of each?

Broctoon

It depends on the type.

There are hubs threaded on only one side. Some have fixed gear threads, and some have single speed threads. A fixed gear thread has the same diameter and pitch as the single speed, but with a second set of threads, outboard, slightly smaller diameter, and the reverse direction (counter-clockwise to tighten). This is where the lock ring goes. The primary or inboard threads are the same on both types. So you can put a single speed freewheel cog on a fixed gear hub with no issues. To put a fixed cog on a single speed hub, where there is no second set of (reverse) threads, you have no good way to keep it from coming loose, which is dangerous. It is easy to do, but it's usually a very bad idea.

Some hubs, called a flip-flop, have both sides threaded. They might be fixed threads on both sides, to allow for two different cog sizes, or fixed on one side and single speed on the other, giving you a choice of drivetrain types. I don't know if anyone makes a flip-flop with single speed on both sides.

If you don't have a flip-flop hub (or fixed gear hub) and you want to ride both types from time to time, you don't need two bikes. You can get two rear wheels. The wheel is easy to change according to your preference for a particular ride.