I have a bike that had been working perfectly until now. I installed new bearings correctly, but as much as I tighten the stem bolts(top cap first), the handlebars will not turn the wheel. If the lift the front wheel up and I turn the fork, the bars turn with it. Any solutions? Edit: Its threadless
Did you get grease on the steer tube of the fork allowing the stem to slip around?
Top cap too tight? Top cap is used to adjust headset. Too loose, fork will flop around and knock. Too tight, it will be hard to turn. Try loosening stem bolts, loosen top cap a bit, retighten stem bolts, and try turning fork. See if that helps.
See “Threadless Headset Adjustment” here:
You might be in need of another spacer, unlikely if everything else is the same (though if you installed new bearings because the old ones were munched that could explain it.
When all else fails, chek ur cabels.