Me and a buddy (Who's done millions, so I know it's done right) installed my T-Belt and I went to check it again since it's been 5000KM.

There's a bit of belt deflection - it's definetely not tight (Like I'd assume it is supposed to be). Is there an acceptable amount of deflection, or is it NOT supposed to have any?

And I assume in order to tighten it I would just push up on the tensioner pulley (With a homemade tool) and tighten the center bolt as I push up?

Run the car for a few minutes and then test the belt immediately after. This gives the tensioner a chance to do it's job and tighten up the belt like it's supposed to. If the car sits in the driveway overnight and then you test it, the belt will be a little bit loose.

That would make sense - I checked it when I changed my thermostat.

I'll check it in my garage tonight after getting home from work.

where are you checking the deflection?? It's different at various parts..
like checking the deflection between the camshaft sprockets would be useless..
also sometimes when you turn the engine off the engine spins backwards if it can't go through with the compression stroke,
when it spins back it compresses the tensioner fully and leaves lots of slack on the other side.

My rule of thumb for setting the tension is the blue tensioner pulley must have it's two adjustment tool holes almost horizontal, just a tiny bit tilted down towards the bumper, I d say 5 degrees. You can also check the tensioner spacing like it says in the VFAQ with a drill bit that's exactly 4mm thick.

Well, I checked it at the cam gears again after I came back from the gym and it was nice and tight up there.

Thanks for the help guys - now at least I know a bit more about how that eccentric pulley works.

I get the same thing when checking the deflection between the cam gear. Sometimes nice nad tight, sometimes up to 1" of deflection, all depends where the engine stops. But when the engine runs and you run you finger over the belt at the top between the cam gears there shouldn't be noticeable deflection, just a smooth running belt. Someone correct me if I'm wrong but that makes sense to me as I've seen recently done belts and not so recently done and the deflection varied a lot with the engine running.