From "The Transformers: Microbots (#2.11)"
[Perceptor, Brawn and Bumblebee, after being reduced to microscopic size, managed to get into Megatron's body, in search for the Heart of Cybertron
The Heart of Cybertron must be in Megatron's chest, and we've got less than two hours to get to it.
Why is that?
Because the reductor beam will wear off, and we'll return to normal size.
] Now you tell us!
Yeah, and Megatron ain't big enough for the three of us.