I had to pull off a water pump pulley and had to hold it while unbolting a shaft but didn't have the special tool or a chain wrench so I decided to make my own since I was in a hurry. It only uses a bicycle chain and a hammer. It won't go around smaller pipes because the size limit is dictated by the hammer and it won't work in spots the hammer won't fit. But it did work for what I wanted so I'm happy. The picture is just a demonstration of the tool on a pipe.

Step 1: Materials

As you can see it only involves a bicycle chain and hammer. There are two ways to make this and I tried both. One way is just to hook the chain inside the claw of the hammer and the other way is to modify the claw a little.

Step 2: Unmodified Hammer

Hopefully you can see how the chain is looped through the claw. The claw should catch the links and hold them in place. It works but a problem with it is the links near the tip of the claw can slip out under pressure. Claws are made differently in hammers so the claw may be too wide or too narrow depending on the hammer.

Step 3: Modified Hammer

For this I used an angle grinder to widen the claw so the groove was parallel and both ends of the chain would slip in deeper. This is the one I used for the water pump pulley and it worked quite well.

Enjoy!