tight chains

[Oblarg]

Worth noting that exact C-C distances on chain don't work quite as well as you might like them to, thanks to chain's annoying habit of relaxing by 10% or so during normal use. My rule of thumb is either to be able to move one of the endpoints of any given run of chain, or to include a tensioner. The former is preferable.

[cadandcookies]

Like Eli said, being able to move your motor mount would probably help significantly with tensioning.

You might also try increasing the size of your sprockets, which would probably help (both with making sure you have solid engagement on your sprockets and minimizing the necessity of tensioning).