From what you are describing, you have two chinchillas that may never get together to be happy as cagemates.
Usually, when two start fighting immediately, they never seem to be able to get along OR it may take a very long time for them to accept each other.
Remember:
Most chinchillas will get along with other chinchillas,
but not all chinchillas will get along with all chinchillas. Chins have personalities just like people. Have you ever met someone that you almost instantly disliked, but weren't sure why? That's a "clash of personalities" ... chinchillas can do this also.
Crash is protecting his home ... chinchillas can be very territorial at times. By Crash humping Rocko, Crash was trying to claim the status of alpha chin (boss chin) ... by trying to bite him while he was doing this ... Rocko was saying ... on, no, I'm gonna be the boss. It looks like you have two chins with dominate personalities.
It will take awhile and lots of patients before they will get along,
if ever. For now, for safety's sake and the health of both chins, they need to stay in separate cages.
If you just got Rocko, aren't you going to isolate him for a period of time to make sure he is healthy before introducing him to Crash?
Where did you get Rocko? Pet store? Breeder? Friend?
Jo Ann