Wheels to Africa teamed up with a Puerto Rican organisation, the JJ Barea Foundation, to organise recipients among local schools, orphanages and others.
There were some logistical glitches. After arriving on Tuesday, the group was told that the shipping container with the bikes was late, and that it would cost far more than the agreed-upon $6000. When they finally sorted it out, it was Thursday evening and they had only two nights and a day to reassemble and fine-tune all the bikes before the giveaway. For 16 hours on Friday, members of the group attached pedals and pumped tires, helped for part of that time by 30 or so local high school students.
On Saturday, local nonprofits and dozens of recipients from around the island showed up. After listening to a talk on bike safety, they were matched with bikes and donated helmets.
"It was a little chaotic - as soon as they got their bikes, they were just having fun riding around the parking lot," said Austin Higgins, a New Jersey resident who recently joined Wheels to Africa as its photographer and videographer. Some recipients were "a little bit overwhelmed, almost speechless," he said.
The donated bikes included some high-end racing models, which went to teenagers interested in pursuing serious cycling.
The sight was familiar to Brian Babilonia, 24, a cyclist who represented Puerto Rico at the 2016 Olympics in Brazil. As a child, Babilonia did not have enough money to buy a bicycle.
"I was one of them," he recalled. "At the beginning I didn't have any gear. People helped me with a helmet and parts so I could (make) my own bike. A few people donated the frame, the wheels."
One pressing issue in Puerto Rico is promoting education of bike safety among riders and also among drivers. "People in Puerto Rico are not very experienced with bicycles and not very aware of them," Babilonia said. "The cars think they are the owner of the road." Local activists are pushing for more bike lanes and posting fliers reminding drivers to leave 1m of space for cyclists, he said. "I hope that one day the road will be very, very good for cyclists."
Alex Wolz, a Wheels to Africa board member who grew up with Duncan and joined the trip, was struck by how happy the kids were to receive the bikes. "One little boy said, 'Oh, I want a red bike.' I picked a red bike off the pile and I brought it over and he just looked at the bike and his jaw dropped," Wolz said.
"I don't think I've ever seen this spirit of community and desire to help your community as I've experienced in Puerto Rico," Wolz said. Particularly since the hurricane, "there is a feeling that you help people, you don't hoard food, and you don't turn inward. You look around to see how you can help."
Harry Valentin, school director of the Ines Maria Mendoza School in Caimito, a rural part of San Juan, said the bicycles given to around 95 of his students will help them get to school more easily. The majority of students there are poor. "Many of them, after Hurricane Maria, they lost a lot of things. Families lost their cars and also their bicycles."
When the students selected to receive bikes were told about it, he said, "Some of them cried, because it was something they had requested for Christmas from Santa Claus or the Three Kings, but they had gone down on Christmas and not seen them."
Duncan, recently graduated from Bard College and is in Arlington, Virginia, working at a political consulting firm. Since his idea took root, he has collected thousands of bicycles from donors in the Washington area.
Recalling his initial trip to Africa, he said, "I was just astounded to see the poverty because I'd never seen anything like that.
"Meeting a kid with holes in his shoes, who had walked four to five miles (6-8km) to get to school, it made me realise how much they appreciate education," he said.
He now encourages kids in the Washington area to get involved with the organisation, and some have joined him on trips to Africa and on this trip to Puerto Rico.
"I wanted to try to get kids in this area to see how privileged we are and to try to get people to think about giving back," he said.
Jake Rabinowitz, 16, of Cleveland Park in Washington joined the organisation in Tanzania and Ghana last year and in Puerto Rico last week.
"You could see on their faces how happy the kids were to get the bikes," said Rabinowitz, a junior at Charles E. Smith Jewish Day School in Maryland. "It's moving to see it, how valuable it is to them."