Is it true cancerous lymph nodes from lymphoma. Typically cause no pain. Grow. Are hard and fixed to a certain area and bigger than 3cm.?

Overgeneralization. Neither the size nor symptoms associated with enlarged lymph nodes will differentiate lymphoma from other causes of lymphadenopathy, including other cancers or other conditions, such as infections. In general, when a lymph node is larger than 1.5-2cm, it is necessary to search for a cause, which may require lymph node biopsy.
Correct... Typically, early cancers/malignancies do not cause pain. Some nodes can be smaller and be cancerous. Often, by the time one experiences pain from the cancer, it usually means it has spread to other organs, especially bones and edges of lungs (breathing causes movement of these areas, thus causing pain).. If you have the nodes above, i suggest getting them checked asap.