We imported two motorbikes into BA in February 2016. Here's what we learned...

Bring:
Passport, Money, Driver’s License (home and international), vehicle registration document, insurance paperwork (we went with ATM, see note below), some petrol, all the tools you need to put your bike back together, a pen, some basic Spanish skills, and a lot of patience (+/- a book). Do not bring large backpacks – they wont let you take them in and there is nowhere to store them.

Process:
Arrive at Termina de Cargas building and collect original airway bill from the airline office that carried your bike. For us this was LAN cargo and cost was AR$3100 (USD $200) per bike.

Go to Senasa office to collect Documento de Madera, there they will send you with a bill to the bank, which you have to pay and return to the semasa office for the document. Cost AR$160 (USD $10).

While you are at bank, there is a little security office next to the entrance of the bank where you need to get a security pass to get through to the next bit. Hand over airway bill and passport and they take a photo and give you a pass for the day.

The next step (after going back to semasa office for documento de Madera) is to go through security to Particulares. Here you will hand over all your documents, speak to someone from customs and eventually you will be asked to pay more money (for first bike it was AR$4200 (USD $220), second bike AR$7300 (USD $480) – apparently they forgot to charge me the dangerous goods tax the first time (even though our bikes were not shipped as dangerous goods and we had a certificate to prove that there was no fuel and battery terminals were taped, they were adamant that all motorbikes were dangerous goods).

Next you inspect your goods and put the bikes back together. This was particularly fun the first day as all of our tools were with the bike that did not arrive, so I was left trying to put a wheel back on, access the battery, etc with no tools. Everyone was super friendly and helpful, running around borrowing what was needed and supplying manpower to help me. I’m a 5’4” female, not 100% sure how well this would go down if you were a guy, but they seemed genuinely helpful so I reckon you’d be fine. Main advice – pack required tools with bike.

One last bit of paperwork back in the particulares office and then you’re free to go. You have to hand some of the paperwork over to the guards on the way out, and you need to keep some for when you leave the country – make sure you know which is which.

Nearest petrol station is in airport but you can’t access it from the termina de cargas so you will need to go out on the autopista and do a blockie (~12km). It’s easy to get “emergency fuel” in a plastic container from any petrol station, which you will need to start the bike to get to the petrol station.

Getting around:
The security guards around the terminal are amazingly friendly and helpful. Just ask “Donde esta…?” and they will often walk you there or at least point you in the right direction. If you don’t have any Spanish, make sure you write down the names of the offices so you can show them to be taken to the right place.

Timing:
The LAN cargo office opens at 0900, but the semasa office doesn’t open until 0930 and the bank doesn’t open until 1000. The first day I arrived at 1030 and I didn’t see my bike until 1545, and didn’t get out until after 1700 (partly due to all the faff putting my bike back together). The second day we arrived at 0900 but had to wait for the semasa office and then the bank to open, but we got the bike by 1200 and out by 1300. My advice would be to get there around 0930 (0830 bus from BA).

Insurance:
ATM insurance office in Buenos Aires. Covers you for third person (vehicle/drivers/passengers/pedestrians), not for your own vehicle or health cover. Cheap and includes riding in all MERCASUR countries. You can’t extend it once you start without going back in person to the office in BA, so we just bought 6 months cover because they do a deal and its cheap. It’s helpful if you can do it 3 days before you leave as it takes a few days for them to be able to print out the official green paper that you need to cross borders. We couldn’t wait three days so he just gave us the green paper without our number on it and said he’d email us the version with the number to print out ourselves. There was also a white paper, which we got straight away with all the necessary details to get through the import/customs side of things, the green one is more for crossing into other countries apparently. We ended up writing in our number by hand, and no-one has complained at the many borders we've crossed.

Have fun out there!

Note: This is under my user-name, but credit to my girlfriend who actually wrote it.