If the saw teeth from long term use it had lost its sharpness and shape, it can be corrected with a file of triangular cross-section or a suitable needle file. But you first need a hacksaw to saw through slightly the angles between the teeth, sharpening will be easier.
Recommend to read
VELOPLIVD WITHOUT “DEAD ZONES”
Improving the efficiency of the drive — a problem which concerned not only the designers of the bikes, but the owners of these cars. Since the invention of the Bicycle pedal drive...
BLACK SEA SHALANDA
"...The barge is loaded mast and folded sail, half pushed into the sea, floated on a light wave... The boys came over and, without much difficulty pushing the barge, jumped into...
