I have a rather stupid question - when you have oversized pistons and rings must you have undersized bearings?

I believe that the bearings only need to be undersized if the crank has been machined.

The reason I ask is that I am planning on re-ringing my Elante after pulling it down and discovering why it seized (a bearing welded to another bearing after falling out of the crank). I noticed that the bearings in the crank were undersized and I am thinking of putting another crank in it, which I guess is standard.

I am not sure as yet if it has been oversized, which is why I am curious if I can run the standard non undersized bearings if the bore is oversized.

There is no relationship between piston size and big-end or main crank bearings.

If you intend to rebuild your engine then it would be a good idea to rebore it and replace the pistons as well, as it isn't that much extra $$$ for pistons. Then you have a new bottom end (use raised flat top pistons to suit TR EFI for more compression).
If you don't know the size of the journals on the crank you intend to use than you will have to get them measured before you order the new bearings.
Might be best to get an engine machine shop to inspect everything including pistons if you want to reuse them. also get them to order the replacement parts for you.
If you replace the pistons get them to also fit the new pistons onto the rods and then you can assemble the rest of the engine

Thanks for the reply ben. I am not totally sure what I am going to do as yet. I think that the engine may have been rebored already, but am not totally sure as yet (need something more accurate to measure it with).

Checked the pistons today - they are 1.00mm oversized anyways :)