Motorcycle repair across the street - legal?

Hi all. My neighbor in Park Slope rents his garage to a group of motorcycle enthusiasts. Unfortunately, they frequently tune and fiddle with their bikes outside, which involves a fair amount of revving. After years of annoyance, I plan to talk to my neighbor and try to get the revving a bit minimized. He’s basically a nice guy and I don’t need a big fight, but in case it comes to it: is this even legal? Renting one garage to multiple people seems shady, as does having repair work spilling out onto the sidewalk.

Thanks!