i think if Y would change the meaning of the entire word, then this Y would be inside the word root itself...so i don´t think it does change the meaning...it must be smth else...

 I´m not an expert, but I think that the past tense of "to be" and the past tense of any other verb are two distinct (although similar) things. Or, at least, they can be seen as two distinct things. For example, at the Manisa Turkish site they are described in two separate chapters:

"To be" past form (applied to nouns/adjectives): -(y)di suffix

http://turkishlanguage.co.uk/tobepos.htm#article_1

"Past tense" (applied to verbs): -di suffix

http://turkishlanguage.co.uk/pasttense.htm

Also, in G.L. Lewis´ "Turkish Grammar" both topics are described separately.

So, answering ally´s question - sentences like "(somebody) was (noun/adjective)" are translated with "-(y)di" suffix, and sentences like "(somebody) (verb-in-the-past-tense)" are translated with "-di" suffix.

 I´m not an expert, but I think that the past tense of "to be" and the past tense of any other verb are two distinct (although similar) things. Or, at least, they can be seen as two distinct things. For example, at the Manisa Turkish site they are described in two separate chapters:

"To be" past form (applied to nouns/adjectives): -(y)di suffix

http://turkishlanguage.co.uk/tobepos.htm#article_1

"Past tense" (applied to verbs): -di suffix

http://turkishlanguage.co.uk/pasttense.htm

Also, in G.L. Lewis´ "Turkish Grammar" both topics are described separately.

So, answering ally´s question - it seems that sentences like "(somebody) was (noun/adjective)" are translated with "-(y)di" suffix, and sentences like "(somebody) (verb-in-the-past-tense)" are translated with "-di" suffix.