we bought two motorbikes in Santiago in Nov 2011,

I cannot help much but what I would say is if you are rush for time, do not use a notario.

they are 2 ways to buy a motorbike in Chile:

1) Use a Notario
2) Go straight to SII building with the current owner

1) NOTARIO:
We did this and it took about 30 days for us to receive the important "padron" which is required to enter some of the countries (it is the ID card of the vehicle with your name and details on it).

Officially all you need is the A4 bit of paper that says that bike is yours. (for this paper it took about 12 days only) You are basicaly waiting for the contract to be checked and approved by the authorities and for their systems to be updated with your name on it.
This paper was enought for us to leave Chile and enter Peru.
For Peru to Bolivia, the official gave us a hard time (as we still didn;t have the "padron" then).
But problem was when we tried to enter Argentina. The chief of Police wouldn;t let us in without the Padron. So we made a fake one from the old one we had (with the name of previous owner on it) and tried the border again and managed to go through.

2) Straight to officials
I am not certain of the procedure as haven;t done it myself.
But as I understand it, you are suppose to go with the current owner to an official building that deals with the name transfer (SII?)
and the idea is that since both parties are present, the contract is aggreed by the authorities straight away and you come out of the building with the system changed and with your "padron" in your name.


I hope this helps.

regards,

Quentin