Solomon and George had beaten the young prospect to death in a bid to "harden him up".
During the two week trial, the Crown said the pair attempted to coax Ratima, a 190cm tall and 130kg man, to fight an associate.
However, both men were reluctant to fight and Solomon and George grew frustrated and launched a savage attack on Ratima.
"They were determined to deal to Mr Ratima," Crown lawyer Natalie Walker told the jury.
Ratima, who had been manning the gate of the gang's Otara pad, was described by witnesses as a "gentle giant".
After not completing his first year of high school, Ratima was changing tyres for a job in South Auckland before he became entangled with the Tribesmen.
After the attack, Solomon and George went to an Auckland "gentlemen's club" and left Ratima with others to take to the emergency department.
He had a swollen brain and two fractures in his neck.
According to a police statement by an associate, Solomon later asked younger gang members to take the fall for the killing, and offered them a motorbike and cash.
However, Solomon's lawyer Shane Tait attempted to discredit the statement and that of other gang associates during the trial.
Solomon and George will be sentenced next month, while Mafu will appear in court again next week.
