Curt, what are the input voltages and how many amperes does it draw? Are you hooking the light bulb up to the output of the dynamotor? I have been playing with dynamotors for about 50 years as well as some very large motor generator sets used for charging industrial batteries and also large DC motor generators used for welding. It doesn't matter to some extent how large or small these devices are as they all operate pretty much on the same principals.
As far as the brushes are concerned, they should have somewhat of a concave shape on them where they meet the commutator. If they do not, they need to be seated with a brush seating stone. The seating stones come in several degrees of hardness but I think for small work, you would use a soft seating stone. It looks like they can still be found by googling them or get them at a motor repair shop. Properly seated brushes should not show too many sparks but all motors/generators will show some sparks depending on the load and the design. The soft stones are white in color. You should blow the motor out with compressed air when done. If you do need to turn the commentator, it will also be
undercut where the mica between each copper segment is cut lower than the surface on the commentator, otherwise it will be spark city and that commentator will get so hot that it will melt the solder connections on the commutator
Terry
https://www.google.com/search?q=brush+seating+stones&oq=brush+seating+stones&aqs=chrome..69i57j0l2.7794j0j8&sourceid=chrome&ie=UTF-8