I've got Trek Crossrip Elite 2014 with VP-V61ACK headset on it and recently changed the top cap to "first" brand. After solved the problem of tightening it, another problem came out. The headset is stiff to turn and not turning smoothly, I know its that I tighten it too much but after loosen it untill it rattles, when I shake it still not turning smoothly as before.

Pls help me out, thanks!

I can't figure out why changing your top cap would have affected how the headset worked. The topcap is just used to preload the bearings, the stem holds everything in place. You should be able to just take off the top cap and toss it in the trash (or stick in a new one as you did) and have no effect on the headset.

So I guess I need to ask: What are you not telling us? What do you mean by "After solved the problem of tightening it"?

EDIT: OK just saw your other thread, so you changed the stem as well?

Just loosen the stem bolts, and tighten the top cap by a 1/4 turn until everything feels good. Not too tight, not too loose. Then re-tighten the stem bolts.

I tried that and even though I tried to loosen it as much as it won't rattle, it still wont turn smoothly

Too tight and it fully stuck, too loose and it rattles and still not moving smoothly

p/s My top cap doesn't interrupt any of my headset, just in-case

Did you take the bearings out during this process....?Did you
put them back upside down?
Photos?

Tough to figure out why this would happen without seeing it. Have you tried taking apart the headset and making sure everything seated correctly?

Cartridge bearing, sealed, [integrated headset] it should not rattle when properly adjusted unless the frame bore has opened up, check with your Trek Dealer.

I don't know how to say this the rattle I'm saying is uhm there's a play when i rock the bike front and back while pressing front brake, the same feeling as loose headset

I got no idea about this but I'll check and upload some photo if possible since no phone ATM

After checking my bottom bearing, I noticed it's upside down and after putting it correctly, the bar turn smoothly again. Problem solved. thanks very much