I was looking over the series and Dinobot could have kill Megatron many times but didn't ?It was like Primal was pretending him from doing it.
Dinobot tried.....and failed. Code of the Warrior I believe it was called when he tried to stop Megatron from killing the pre-humans and died in the proccess. He might have had a slim chance before Megatron became a Transmetal but even then it would have been slim to none. I don't recall Primal exactly preventing him either.
Because Dinobot was hedging his bets that Megatron would succeed in his plans. That's why he returned the Golden Disks to Megatron. Evidently Dinobot was the only crewmember of the Darksyde with whom Megatron shared the real reason for their mission, though he allowed Tarantulas to 'discover' it.