Zincir yağı arka aktarıcıda kullanıldı.

Because Turkish often uses a noun compound for this kind of meaning.

• zincir = chain
• yağ = oil
• zincir yağı = chain oil / oil for a chain

This is a very common pattern in Turkish:

• first noun stays plain
• second noun takes a compound ending, here -ı

So zincir yağı is more natural than zincirin yağı if you mean the type of oil, not the oil belonging to a specific chain.

Compare:

• zincir yağı = chain oil, oil used for chains
• zincirin yağı = the chain’s oil, the oil of the chain

It is arka aktarıcı + -da.

• arka = rear, back
• aktarıcı = derailleur
• -da = locative suffix, meaning something like in / on / at

So arka aktarıcıda means on the rear derailleur or in the rear derailleur, depending on the natural English translation.

Turkish -da/-de is broader than any one English preposition, so the exact English choice depends on context.

This depends on two rules:

1. Vowel harmony
   The last vowel in aktarıcı is ı, a back vowel, so the suffix uses a:

   • -da

2. Consonant voicing
   The word ends in a vowel, so the suffix keeps d, not t.

So:

• aktarıcı + da → aktarıcıda

Very roughly:

• -da / -de after vowels or voiced consonants
• -ta / -te after voiceless consonants

Because kullanıldı contains the passive marker.

It comes from:

• kullanmak = to use
• kullanılmak = to be used
• kullanıldı = was used

Breakdown:

• kullan- = use
• -ıl- = passive
• -dı = past tense

So the sentence is literally structured like:

• Chain oil
  • on the rear derailleur
    • was used

The grammatical subject is zincir yağı.

In a passive sentence, the thing affected by the action often becomes the subject:

• Zincir yağı ... kullanıldı.
• Chain oil ... was used.

The person who used it is not mentioned.

If Turkish wanted to say who did it, it would usually need a different structure, often an active one.

Because Turkish does not normally use articles like English a/an/the.

So:

• zincir yağı can mean chain oil, the chain oil, or some chain oil
• arka aktarıcıda can mean on the rear derailleur or on a rear derailleur

The exact meaning is understood from context.

Sometimes bir can mean a/an or one, but it is not required in sentences like this.

No, Turkish word order is flexible, although some orders are more neutral than others.

This sentence:

• Zincir yağı arka aktarıcıda kullanıldı.

is perfectly natural. But Turkish could also say:

• Arka aktarıcıda zincir yağı kullanıldı.

Both mean the same basic thing. The difference is mainly emphasis or information flow.

Very generally:

• what comes earlier is often the topic or known information
• what comes right before the verb is often emphasized

It is written as two words.

• arka = rear/back
• aktarıcı = derailleur

Together they mean rear derailleur.

When a suffix is added, it usually goes on the last word:

• arka aktarıcı
• arka aktarıcıda

This is normal for many Turkish noun phrases.

Yes, depending on context.

The Turkish locative suffix -da/-de does not map perfectly to just one English preposition. It can correspond to:

• in
• on
• at

So a learner should not expect a one-to-one match. In this sentence, English most naturally says something like:

• on the rear derailleur or
• in the rear derailleur

but Turkish simply uses the locative suffix.

An active version would need someone doing the action, for example:

• Birisi arka aktarıcıda zincir yağı kullandı.
  = Someone used chain oil on the rear derailleur.

Or, more naturally depending on the situation:

• Birisi arka aktarıcıya zincir yağı sürdü.
  = Someone applied chain oil to the rear derailleur.

So the passive kullanıldı is useful when the doer is unknown, unimportant, or simply omitted.

A rough pronunciation guide:

• Zincir ≈ ZEEN-jeer
• yağı ≈ yah-uh or yaa-uh
  (the ğ usually does not sound like a strong consonant)
• arka ≈ AR-kah
• aktarıcıda ≈ ahk-tuh-ruh-juh-duh
• kullanıldı ≈ kool-lah-nuhl-duh

A few useful notes:

• c in Turkish sounds like English j in jam
• ı is a vowel English does not really have; it is a dull, central vowel
• ğ often lengthens or smooths the vowel rather than making a strong sound

The base word is yağ = oil.

When suffixes are added, the final ğ stays in spelling:

• yağ
• yağı

In pronunciation, ğ usually becomes very soft or disappears as a clear consonant sound. So learners often notice that yağı does not sound like it has a hard g.

This is normal in Turkish and happens in many words with ğ.