This topic was addressed by Dr. Monzer Kahf, Scholar in Islamic Economics & Financial Expert, and stated
“Texts from the Qur’an and Sunnah on the prohibition of Riba are well known and also available on the Web, including my own web page.
to answer the question: it seems to me that you agreed with your partner on not being a part of the interest loan and on owning only 14% of the property. How can you go back to 50%? I suppose if this is the agreement between you the two partners, then your share of the rent and ownership and sale price is only 14%; it goes all along until you sell.
Of course if your partner agrees to give you the difference that brings you back to 50% this amounts to a sale and you can agree on any price to do that.
Last, it seems that you are keen to abide by the rules of Shari`ah and this is highly rewarded by Allah.”