I created a single chain link from a shape layer, then drew a mask path around the outside of the chainsaw's bar, copied the mask path and pasted it to the chain link's Position.
This way I got a single chain link traveling around the chainsaw bar. After this, I precomposed the chain link layer and applied Echo effect. Now some 40 chain links are traveling around the chainsaw bar, creating pretty decent illusion of a rotating chainsaw's chain.
However, I dont know how to control the speed of this rotating chain. At some intervals I want it rotate faster, then slower, and then stop. How could i achieve this? I know it's possible to adjust Time Stretch under layer properties, but it's not animatable (ie you cannot put keyframes on this property). Maybe some expression?