The bearings fit very tightly, but they do go in . A hammer is definately NOT necessary, either!
I have not weighed the idlers, so I am unsure of the actual weight. I will weigh them for you.

uhhh did i damage the idlers by hammering it???

I doubt you damaged anything(except maybe the bearings). If the idler spins with no resistance, tye bearings are fine. I know the bearings were snug. The heat treatment likely changed the inside diameter just enough to tighten things up.

hmmm....I have a problem with one of my idlers. The inside of it is very rough, and it has no ring in the middle. I can fit one bearing inside it, but because there's no ring in the middle the bearing moves about and the ilders doesn't sit in line with the other gears. What should I do?

Hopefully this pic explain all

Can you push the bearing all the way through? Can you get a bearing in either side? It does look a bit rough on the inside, actually, but I see a slight ring in the middle, which should locate the bearings. The bearings are a tight fit, due to the hardening process. I have made an adjustment on the next batch to compensate for this.

I can easily get one bearing in. The other bearing goes about 2/3's of the way in, but there is a little lump (not shown in the photo) that stops it going any further. The little ring that you described you thought you could see does nothing. The bearing that I can fit in pushes as far up the hole and the lump (which stops the other bearing going in.
I'm going to see if I can dremel the little lump away. Thanks for your help.

Problem solved.....yet again the dremel saved the day. Tranny runs nice 'n' smooth now. :D