MAHAMANTRA

I chant the Mahamantra when at work. Is it fine to chant in the mind or should I chant only by opening my mouth?

What you are doing is perfectly right.

I chant Nama daily. My father says that we should not face South direction while reciting slokas or while chanting. Is it correct? Why is it so?

South is the direction of the Pitrus (dead ancestors). Hence that direction is usually avoided for all spiritual practices. However, for Mahamantra Kirtan, there are no rules or regulations. That is the greatness of this path.

Chaitanya Mahaprabhu advocated the Mahamantra as “Hare Krishna…Hare Rama”, while you are preaching the Mahamantra as “Hare Rama…Hare Krishna”. What is the difference?

The Mahamantra “Hare Rama…” is found in the Kali Santarana Upanishad.
Upanishads are held sacred and are regarded as the highest form of Jnana. The Shastras say that the Vedas and Upanishads can be learnt and chanted only by a specific sect of people, because of the rigorous tone and intonation involved.
Mahaprabhu, a great mahan that he was, did want to liberate the masses from this ocean of Samsara through the Mahamantra, and at the same time not violate the Shastras. Hence he preached it as
Hare Krishna Hare Krishna Krishna Krishna Hare Hare Hare Rama Hare Rama Rama Rama Hare Hare
When repeated continuously, this indeed reads the same way as stated by the Upanishads.
There are other Saints and Mahans, like Swami Abhedananda of Tiruvananthapuram and innumerable saints of Brindavan who have, out of their sheer mercy and compassion given the Mahamantra as is from the Upanishads, as in this Kali Yuga where none of the rules laid out in the Shastras can be practically followed in spirit.
Thus, irrespective of the way in which it is chanted, it gives the same benefit.

I am chanting Mahamantra and I am interested in spreading it to my friends. Is it right to tell about it to a person who is not interested? I am trying to tell to my friends but some are in vain. How can tell them to chant Mahamantra?

Before you go out for this task, first, pray to Lord Krishna. He will make it successful for you. Even those who are not interested now may change in future. Who knows! Our duty is only to take the Nama to people. We will not bother about the results. We are not making anyone chant. It is Lord Krishna who does that. So everything will happen according to His wish.

What is the difference mahamantra and Rama Nama?

Rama Nama is in Mahamantra

“Hare Rama Hare Rama Rama Rama Hare Hare Hare Krishna Hare Krishna Krishna Krishna Hare Hare” What is the meaning of HARE?

“Hare” refers to Lord Narasimha.

Which one is better – Mahamantra Japa or Mahamantra Kirtan?

Mahamantra Kirtan is Mahamantra Japa.

When is the best time to chant the Mahamantra? Must it be chanted for 108 times only or can we chant as we wish?

You can chant the Mahamantra any time. The more you chant, the closer you get to your goal.

In one of your answers, it is said that five bodies cover the Atman and shattering the five bodies makes one Jeevan Mukta . Can I reach that stage by chanting only Maha Mantra?

Yes there is no doubt about it.

While chanting the Mahamantra, my mind wanders, but still the mouth chants. Will there be any effect?

Definitely. Continue it. You will experience the bliss by yourself.