Splitting engine cases without disturbing top end?

[hillsy]

As the title suggests, I've got some weird noises coming from the starter clutch / primary chain and I understand this requires the cases split to access.

Is it possible to split them from the bottom to access or do I have to tear down from the top? Don't want to have to buy new top end gaskets if I can do the job with the top end intact.

Cheers.....hillsy