"Arny Krueger" said:

Generally, needle bearings are adjustable. The needles are threaded and
slotted for a screwdriver. Beware of over-tightening.

The bearings in a tonearm are relatively heavily preloaded by the weight of
the arm. This is not the front suspension of a car where the bearings can
have a negative load. Therefore, it generally doesn't matter if they are a
little loose, unless they get so loose that there are alignment or friction
problems.

Loose bearings will alter the resonance frequency of the tone arm, as
well as increase the amplitude of resonances because of ineffective
transfer of energy at the needle's points.

Generally, they can make a cart-arm combo sound like ****.

--
Sander deWaal
Vacuum Audio Consultancy